Hemophilia A is an X-linked recessive bleeding disorder caused by a deficiency in the activity of coagulation factor VIII. The disorder is clinically heterogeneous with variable severity, depending on the plasma levels of coagulation factor VIII: mild, with ... Hemophilia A is an X-linked recessive bleeding disorder caused by a deficiency in the activity of coagulation factor VIII. The disorder is clinically heterogeneous with variable severity, depending on the plasma levels of coagulation factor VIII: mild, with levels 6 to 30% of normal; moderate, with levels 2 to 5% of normal; and severe, with levels less than 1% of normal. Patients with mild hemophilia usually bleed excessively only after trauma or surgery, whereas those with severe hemophilia have an annual average of 20 to 30 episodes of spontaneous or excessive bleeding after minor trauma, particularly into joints and muscles. These symptoms differ substantially from those of bleeding disorders due to platelet defects or von Willebrand disease (193400), in which mucosal bleeding predominates (review by Mannucci and Tuddenham, 2001).
The severity and frequency of bleeding in hemophilia A is inversely related to the amount of residual factor VIII in the plasma: less than 1% factor VIII results in severe bleeding, 2 to 6% results in moderate bleeding, ... The severity and frequency of bleeding in hemophilia A is inversely related to the amount of residual factor VIII in the plasma: less than 1% factor VIII results in severe bleeding, 2 to 6% results in moderate bleeding, and 6 to 30% results in mild bleeding. The proportion of cases that are severe, moderate, and mild are about 50, 10, and 40%, respectively, The joints are frequently affected, causing swelling, pain, decreased function, and degenerative arthritis. Similarly, muscle hemorrhage can cause necrosis, contractures, and neuropathy by entrapment. Hematuria occurs occasionally and is usually painless. Intracranial hemorrhage, while uncommon, can occur after even mild head trauma and lead to severe complications. Bleeding from tongue or lip lacerations is often persistent (review by Antonarakis et al., 1995). The clinical hallmarks of hemophilia A are joint and muscle hemorrhages, easy bruising, and prolonged hemorrhage after surgery or trauma, but no excessive bleeding after minor cuts or abrasions. Affected individuals may have little bleeding during the first year of life, but develop hemarthroses when beginning to walk. The most frequently affected joints are the knees, elbows, ankles, shoulders, and hips. Hemophilic arthropathy can be a progressive inflammatory condition which may result in limitation of motion and permanent disability (review by Hoyer, 1994). - Female Carriers Rapaport et al. (1960) demonstrated a partial deficiency of factor VIII in heterozygous female carriers. Most heterozygous female carriers of hemophilia A or hemophilia B (306900) have concentrations of clotting factor VIII or IX (F9; 300746) of about 50% of normal, respectively, and in most cases have mildly decreased coagulability without clinical signs. Sramek et al. (2003) followed up a cohort of 1,012 mothers of all known people with hemophilia in the Netherlands from birth to death, or the end-of-study date (41,984 person years of follow-up). Overall mortality was decreased by 22%. Deaths from ischemic heart disease were reduced by 36%. No decrease in mortality was observed for cerebral stroke (ischemic and hemorrhagic combined). Women in the cohort had an increased risk of deaths from extra cranial hemorrhage; however, the number of deaths from this cause was much lower than that for ischemic heart disease. The results were interpreted as showing that a mild decrease in coagulability has a protective effect against fatal ischemic heart disease. In a population-based survey in the Netherlands, Plug et al. (2006) found that female carriers of hemophilia A and B bled more frequently than noncarrier women, especially after medical procedures, such as tooth extraction or tonsillectomy. Reduced clotting factor levels correlated with a mild hemophilia phenotype. Variation in clotting levels was attributed to lyonization.
In a Japanese family with mild to moderately severe hemophilia A, Young et al. (1997) found a deletion of a single nucleotide T within an A(8)TA(2) sequence of exon 14 of the F8 gene. The severity of the ... In a Japanese family with mild to moderately severe hemophilia A, Young et al. (1997) found a deletion of a single nucleotide T within an A(8)TA(2) sequence of exon 14 of the F8 gene. The severity of the clinical phenotype did not correspond to that expected of a frameshift mutation. A small amount of functional factor VIII protein was detected in the patient's plasma. Analysis of DNA and RNA molecules from normal and affected individuals and in vitro transcription/translation suggested a partial correction of the molecular defect, because of the following: (i) DNA replication/RNA transcription errors resulted in restoration of the reading frame and/or (ii) 'ribosomal frameshifting' resulted in the production of normal factor VIII polypeptide and, thus, in a milder-than-expected hemophilia A. All of these mechanisms probably were promoted by the longer run of adenines, A(10) instead of A(8)TA(2), after the deleted T. Young et al. (1997) concluded that errors in the complex steps of gene expression therefore may partially correct a severe frameshift defect and ameliorate an expected severe phenotype. Cutler et al. (2002) identified 81 mutations in the F8C gene in 96 unrelated patients, all of whom had previously typed negative for the common IVS22 inversion mutation (306700.0067). Forty-one of these mutations were not recorded in F8C gene mutation databases. Analysis of these 41 mutations with regard to location, possible cross-species conservation, and type of substitution, in correlation with the clinical severity of the disease, supported the view that the phenotypic result of a mutation in the F8C gene correlates more with the position of the amino acid change within the 3-dimensional structure of the protein than with the actual nature of the alteration.
Ratnoff and Bennett (1973) reviewed the genetics of hereditary disorders of blood coagulation.
Gitschier et al. (1985) identified truncating mutations in the F8 gene (see, e.g., 300841.0001-300841.0003) as the basis for hemophilia A. A severe hemophiliac ... Ratnoff and Bennett (1973) reviewed the genetics of hereditary disorders of blood coagulation. Gitschier et al. (1985) identified truncating mutations in the F8 gene (see, e.g., 300841.0001-300841.0003) as the basis for hemophilia A. A severe hemophiliac with no detectable factor VIIIC activity had an R2307X mutation (306700.0001). Gitschier et al. (1986) found that the same codon was converted to glutamine (R2307Q; 306700.0042) in a mild hemophiliac with 10% of normal activity. A diminished level of factor VIII Ag in the latter patient coincided with the level of clotting activity, suggesting that the abnormal factor VIII was relatively unstable. In a study of 83 patients with hemophilia A, Youssoufian et al. (1986) identified 2 different point mutations, one in exon 18 and one in exon 22, that recurred independently in unrelated families. Each mutation produced a nonsense codon by a change of CG to TG. In the opinion of Youssoufian et al. (1986), these observations indicated that CpG dinucleotides are mutation hotspots. It had been postulated that methylated cytosines may be mutation hotspots because 5-methylcytosine can spontaneously deaminate to thymine, resulting in a C-to-T transition in DNA. Youssoufian et al. (1987) characterized 5 different partial deletions of the F8 gene in 83 patients with hemophilia. None had developed circulating inhibitors. One of the deletions occurred de novo in a germ cell of the maternal grandmother, while a second deletion occurred in a germ cell of a maternal grandfather. The findings indicated that de novo deletions of X-linked genes can occur in either male or female gametes. Youssoufian et al. (1988) reported 6 other partial F8 gene deletions in severe hemophilia A, bringing to 12 the number of deletions among 240 patients. No association was observed between the size or location of deletions and the presence of inhibitors to factor VIII. Furthermore, no 'hotspots' for deletion breakpoints were identified. Youssoufian et al. (1988) screened 240 patients with hemophilia A and found CG to TG transitions in an exon in 9. They identified novel missense mutations leading to severe hemophilia A and estimated that the extent of hypermutability of CpG dinucleotides is 10 to 20 times greater than the average mutation rate for hemophilia A. Cooper and Youssoufian (1988) collated reports of single basepair mutations within gene coding regions causing human genetic disease. They found that 35% of mutations occurred within CpG dinucleotides. Over 90% of these mutations were C-to-T or G-to-A transitions, which thus occur within coding regions at a frequency 42-times higher than that predicted from random mutation. Cooper and Youssoufian (1988) believed these findings were consistent with methylation-induced deamination of 5-methylcytosine and suggested that methylation of DNA within coding regions may contribute significantly to the incidence of human genetic disease. Higuchi et al. (1988) found deletion of about 2,000 bases spanning exon 3 and part of IVS3 of the F8 gene in a patient with severe hemophilia A. The mother was judged to be a somatic mosaic because the defective gene could be identified in only a portion of the leukocytes and cultured fibroblasts. In a review, Antonarakis et al. (1995) collected the findings of more than 1,000 hemophilia subjects examined for F8 gene mutations. These include point mutations, inversions, deletions, and unidentified mutations which constitute 46%, 42%, 8%, 4%, and 91%, 0%, 0%, and 9%, respectively, of those with severe versus mild to moderate disease, respectively, in selected studies. The 266 point mutations described as of April, 1994 comprised missense (53%), CpG-to-TpG (16%), small deletions (12%), nonsense (9%), small inversions and splicing (3% each), and missense polymorphisms and silent mutations in exons (2% each). In addition to these point mutations 100 different larger deletions and 9 insertion mutations had been reported. In a study of 147 sporadic cases of severe hemophilia A, Becker et al. (1996) were able to identify the causative defect in the F8 gene in 126 patients (85.7%). An inversion of the gene was found in 55 patients (37.4%), a point mutation in 47 (32%), a small deletion in 14 (9.5%), a large deletion in 8 (5.4%), and a small insertion in 2 (1.4%). In 4 (2.7%), mutations were localized but not yet sequenced. No mutation was identified in 17 patients (11.6%). The identified mutations occurred in the B domain in 16 (10.9%); 4 of these were located in an adenosine nucleotide stretch at codon 1192, indicating a mutation hotspot. Somatic mosaicism was detected in 3 (3.9%) of 76 patients' mothers, comprising 3 of 16 de novo mutations in the patients' mothers. Investigation of family relatives allowed detection of a de novo mutation in 16 of 76 2-generation and 28 of 34 3-generation families. On the basis of these data, Becker et al. (1996) estimated the male:female ratio of mutation frequencies (k) to be 3.6. By use of the quotients of mutation origin in maternal grandfather to patients' mother or to maternal grandmother, k values were directly estimated as 15 and 7.5, respectively. Considering each mutation type separately, they found a mutation type-specific sex ratio of mutation frequencies. Point mutations showed a 5-to-10-fold-higher and inversions a more than 10-fold-higher mutation rate in male germ cells, whereas deletions showed a more than 5-fold-higher mutation rate in female germ cells. Consequently, and in accordance with the data of other disorders such as Duchenne muscular dystrophy, the results indicated to Becker et al. (1996) that at least for X-chromosomal disorders the male:female mutation rate is determined by its proportion of the different mutation types. The molecular diagnosis of hemophilia A is challenging because of the high number of different causative mutations that are distributed through the large F8 gene. The putative role of the novel mutations, especially missense mutations, may be difficult to interpret as causing hemophilia A. Guillet et al. (2006) identified 95 novel mutations out of 180 different mutations found among 515 patients with hemophilia A from 406 unrelated families followed up at a single hemophilia treatment center in a Paris hospital. The 95 novel mutations comprised 55 missense mutations, 12 nonsense mutations, 11 splice site mutations, and 17 small insertions/deletions. They used a strategy in interpreting the causality of novel F8 mutations based on a combination of the familial segregation of the mutation, the resulting biologic and clinical hemophilia A phenotype, and the molecular consequences of the amino acid substitution. For the latter, they studied the putative biochemical modifications: its conservation status with cross-species factor VIII and homologous proteins, its putative location in known factor VIII functional regions, and its spatial position in the available factor VIII 3D structures. Among 1,410 Italian patients with hemophilia A, Santacroce et al. (2008) identified 382 different mutations in the F8 gene, 217 (57%) of which had not previously been reported. Mutations leading to a null allele accounted for 82%, 15%, and less than 1% of severe, moderate, or mild hemophilia, respectively. Missense mutations were identified in 16%, 68%, and 81% of severe, moderate, or mild hemophilia, respectively, yielding a good genotype/phenotype correlation useful for treatment and genetic counseling. In order to establish a national database of F8 mutations, Green et al. (2008) identified and cataloged multiple mutations in approximately one-third of the U.K. hemophilia A population. The risk of developing inhibitors for patients with nonsense mutations was greater when the stop codon was in the 3-prime half of the mRNA. The most common change was the intron 22 inversion (306700.0067), which accounted for 16.6% of all mutations and for 38% of those causing severe disease. - Inversion Mutations in Intron 22 of the F8 Gene Intron 22 of the human F8 gene is hypomethylated on the active X and methylated on the inactive X. Inaba et al. (1990) described an MspI RFLP in intron 22 of the F8 gene. Japanese showed 45% heterozygosity and Asian Indians showed 13%; polymorphism was not found in American blacks or Caucasians. Naylor et al. (1992) found an unusual cluster of mutations involving regions of intron 22 not examined earlier and leading to defective joining of exons 22 and 23 in the mRNA (300841.0067) as the cause of hemophilia A in 10 of 24 severely affected UK patients. These results confirmed predictions about the efficacy of the mRNA-based method suggested by Naylor et al. (1991), and also excluded hypotheses proposing that mutations outside the F8 gene are responsible for a large proportion of severe hemophilia A. Of the 28 patients reported by Naylor et al. (1993), 5 had mild or moderate disease and all had a missense mutation. The other 23 patients were severely affected; unexpectedly, intron 22 seemed to be the target of approximately 40% of the mutations causing severe hemophilia A. Naylor et al. (1993) found that the basis of the unique F8 mRNA defect that prevented PCR amplification across the boundary between exons 22 and 23 was an abnormality in the internal regions of intron 22. They showed that exons 1-22 of the F8 mRNA had become part of a hybrid message containing new multi-exonic sequences expressed in normal cells. The novel sequences were not located in a YAC containing the whole F8 gene. Southern blots from patients probed by novel sequences and clones covering intron 22 showed no obvious abnormalities. Naylor et al. (1993) also suggested that inversions involving intron 22 repeated sequences are the basis of the mRNA defect. These mutations in severely affected patients occur at the surprising rate of approximately 4 x 10(-6) per gene per gamete per generation. Furthermore, it has been shown that these de novo inversions occur more frequently in males than females with a ratio of 302:1 estimated in male:female germ cells. The F8A gene (305423) is contained entirely within intron 22 of the F8 gene and is transcript in the reverse orientation from the F8 gene (Levinson et al., 1990). Lakich et al. (1993) proposed that many of the previously unidentified mutations resulting in severe hemophilia A are based on recombination between the homologous F8A sequences within intron 22 and upstream of the F8 gene. Such a recombination would lead to an inversion of all intervening DNA and a disruption of the gene. Lakich et al. (1993) presented evidence to support this model and described a Southern blot assay that detects the inversion. They suggested that this assay should permit genetic prediction of hemophilia A in approximately 45% of families with severe disease. Inversion mutations resulting from recombinations between DNA sequences in the A gene in intron 22 of the F8 gene and 1 of 2 other A genes upstream to F8 have been shown to cause a large portion of cases. From data on more than 2,000 samples, Antonarakis et al. (1995) concluded that the common inversion mutations are found in 42% of all severe hemophilia A subjects. Whereas 98% of the mothers of those with inversions were carriers of the inversion, only about 1 de novo inversion was found in maternal cells for every 25 mothers of sporadic cases. When the maternal grandparental origin of inversions was examined the ratio of de novo occurrences in male:female germ cells was 69:1. Brinke et al. (1996) reported the presence of a novel inversion in 2 hemophilic monozygotic twins. These patients showed an inversion that affects the first intron of the F8 gene, displacing the most telomeric exon (exon 1) of F8 further towards the telomere and close to the C6.1A gene (BRCC3; 300617). Brinke et al. (1996) noted that this novel inversion creates 2 hybrid transcription units. One of these is formed by the promoter and first exon of F8 and widely expressed sequences that map telomeric to the C6.1A sequence. The other hybrid transcription unit contains the CpG island and all of the known sequence of C6.1A and the 3-prime section of most of the F8 gene. It is hypothesized that the inversion mutations occur almost exclusively in germ cells during meiotic cell division by an intrachromosomal recombination between a 9.6-kb sequence within intron 22 and 1 of 2 almost identical copies located about 300 kb distal to the F8 gene at the telomeric end of the X chromosome. Most inversion mutations originate in male germ cells, where the lack of bivalent formation may facilitate flipping of the telomeric end of the single X chromosome. Oldenburg et al. (2000) reported the first instance of intron 22 inversion presenting as somatic mosaicism in a female, affecting only about 50% of lymphocyte and fibroblast cells of the proposita. Supposing a postzygotic de novo mutation as the usual cause of somatic mosaicism, the finding implies that the intron 22 inversion mutation is not restricted to meiotic cell divisions but can also occur during mitotic cell divisions, either in germ cell precursors or in somatic cells. - Development of Factor VIII Inhibitors Approximately 10 to 20% of patients with severe hemophilia A develop antibodies, known as inhibitors, to factor VIII following treatment with with exogenous factor VIII. Most of these patients have nonsense mutations or deletions in the F8 gene (Antonarakis et al., 1995). Antonarakis et al. (1985) identified several molecular defects in families with hemophilia A. One family had a deletion of about 80 kb in the F8 gene, whereas another had a single nucleotide change in the coding region of the gene, resulting in a nonsense codon and premature termination. In addition, they used 2 common polymorphic sites in the F8 gene to differentiate the normal gene from the defective gene in 4 of 6 obligate carriers from families with patients in whom inhibitors did not develop. In both the family with a large deletion and the family with premature termination, affected persons developed inhibitors. A variety of F8 gene mutations have been found in patients with hemophilia A due to inhibitors. Among 30 such cases, Antonarakis et al. (1995) found that 87 and 13% had different nonsense and missense mutations, respectively. F8 gene inversions do not seem to be a major predisposing factor for the development of inhibitors. Among severe hemophilia A cases, 16% of those without inversions and 20% of those with inversions developed inhibitors. Schwaab et al. (1995) found that the probability of developing factor VIII inhibitors is greater in patients with large deletions in the F8 gene. Viel et al. (2009) sequenced the F8 gene in 78 black patients with hemophilia to identify the causative mutations and background haplotypes, which the authors designated H1 to H5. They found that 24% of the patients had an H3 or H4 haplotype, and that the prevalence of inhibitors was higher among patients with either of those haplotypes than among patients with haplotypes H1 or H2 (odds ratio, 3.6; p = 0.04), despite a similar spectrum of hemophilic mutations and degree of severity of illness in the 2 subgroups. Noting that Caucasians carry only the H1 or H2 haplotypes and that most blood donors are Caucasian, Viel et al. (2009) suggested that mismatched factor VIII replacement therapy might be a risk factor for the development of anti-factor VIII alloantibodies.
The incidence of hemophilia A, caused by a deficiency of factor VIII, is estimated at about 1 in 5,000 male live births. Hemophilia B, caused by a deficiency of factor IX, is estimated at about 1 in 30,000 ... The incidence of hemophilia A, caused by a deficiency of factor VIII, is estimated at about 1 in 5,000 male live births. Hemophilia B, caused by a deficiency of factor IX, is estimated at about 1 in 30,000 male live births (Mannucci and Tuddenham, 2001). Soucie et al. (1998) studied the frequency of hemophilia A and hemophilia B in 6 U.S. states: Colorado, Georgia, Louisiana, Massachusetts, New York, and Oklahoma. A hemophilia case was defined as a person with physician-diagnosed hemophilia A or B and/or a measured baseline factor VIII or IX activity (FA) of 30% or less. Case-finding methods included patient reports from physicians, clinical laboratories, hospitals, and hemophilia treatment centers. Once identified, trained data abstractors collected clinical and outcome data retrospectively from medical records. Among cases identified in 1993 to 1995, 2,743 were residents of the 6 states in 1994, of whom 2,156 (79%) had hemophilia A. Of those with factor VIII measurements, 1,140 (43%) had severe (FA less than 1%), 684 (26%) had moderate (FA of 1-5%), and 848 (31%) had mild (FA of 6-30%) disease. The age-adjusted prevalence of hemophilia in all 6 states in 1994 was 13.4 cases per 100,000 males (10.5 hemophilia A and 2.9 hemophilia B). The prevalence by race/ethnicity was 13.2 cases per 100,000 white, 11.0% among African American, and 11.5% among Hispanic males. Application of age-specific prevalence rates from the 6 surveillance states to the U.S. population resulted in an estimated national population of 13,320 cases of hemophilia A and 3,640 cases of hemophilia B. For the 10-year period 1982 to 1991, the average incidence of hemophilia A and B in the 6 surveillance states was estimated to be 1 in 5,032 live male births.
A specific diagnosis of hemophilia A cannot be made on clinical findings. A coagulation disorder is suspected in individuals with any of the following:...
DiagnosisClinical DiagnosisA specific diagnosis of hemophilia A cannot be made on clinical findings. A coagulation disorder is suspected in individuals with any of the following:Hemarthrosis, especially with mild or no antecedent trauma Deep-muscle hematomas Intracranial bleeding in the absence of major trauma Neonatal cephalohematoma or intracranial bleeding Prolonged oozing or renewed bleeding after initial bleeding stops following tooth extractions, mouth injury, or circumcision *Prolonged or delayed bleeding or poor wound healing following surgery or trauma *Unexplained GI bleeding or hematuria * Menorrhagia, especially with onset at menarche (in symptomatic carriers) *Prolonged nosebleeds, especially recurrent and bilateral *Excessive bruising, especially with firm, subcutaneous hematomas * Of any severity, or especially in more severely affected personsTestingCoagulation screening tests. Evaluation of an individual with a suspected bleeding disorder includes: platelet count and platelet function analysis (PFA closure times) or bleeding time; activated partial thromboplastin time (APTT); and prothrombin time (PT), a screen for the extrinsic clotting system. Thrombin time and/or plasma concentration of fibrinogen can be useful for rare disorders. In individuals with hemophilia A, the above screening tests are normal, with the following exceptions: The APTT is prolonged in severe and moderate hemophilia A. Prolongations in APTT that correct on mixing with an equal volume of normal plasma indicate an intrinsic system clotting factor deficiency, including factor VIII, without an inhibitor. Note: It is important to confirm the diagnosis of hemophilia A and to exclude other deficiencies with a specific factor VIII clotting activity assay, which is available in most hospital laboratories or coagulation reference laboratories. The APTT may be normal but is usually mildly prolonged in mild hemophilia A. The prothrombin time (PT) should be normal unless another hemostatic defect such as liver disease is present.Note: In some clinical laboratories, the APTT is not sensitive enough to diagnose mild hemophilia A.Coagulation factor assays. Individuals with a history of a lifelong bleeding tendency should have specific coagulation factor assays performed even if all the coagulation screening tests are in the normal range: The normal range for factor VIII clotting activity is approximately 50% to 150%. Individuals with factor VIII clotting activity higher than 30% usually do not have bleeding [Kaufman et al 2006]. However, a mild bleeding tendency can occur with low to low-normal factor VIII clotting activity in hemophilia A carrier females [Plug et al 2006] or in those with mild von Willebrand disease. The risk of having a bleeding tendency appears to be higher in carriers of alleles associated with severe hemophilia A, regardless of the baseline factor VIII clotting activity [Miesbach et al 2011].In hemophilia A, the factor VIII clotting activity is usually lower than 30%-35% with a normal, functional von Willebrand factor level. Classification of hemophilia A based on in vitro clotting activity: Severe hemophilia A. <1% factor VIII Moderate hemophilia A. 1%-5% factor VIII Mild hemophilia A. 6%-35% factor VIII Note: Rarely, in individuals with mild hemophilia A, a standard "one-stage" factor VIII clotting activity assay shows near-normal or low-normal factor VIII clotting activity (40%-80%), whereas in a "two-stage" or chromogenic assay, factor VIII activity is low. Thus, low-normal in vitro clotting activity does not always exclude the presence of mild hemophilia A. Carrier femalesCoagulation factor assays. Approximately 10% of hemophilia A carrier females have factor VIII clotting activity lower than 35% regardless of the severity of hemophilia A in the family. Bleeding may also be more severe in those with low-normal factor VIII activity [Plug et al 2006]. Factor VIII clotting activity is unreliable in the detection of hemophilia A carriers:Factor VIII clotting activity in plasma is increased with pregnancy, oral contraceptive use, aerobic exercise, and chronic inflammation. Factor VIII clotting activity in plasma is approximately 25% lower in individuals of blood group O than in individuals of blood groups A, B, or AB. The majority of obligate carriers, even of severe hemophilia A, have normal factor VIII clotting activities.Molecular Genetic TestingGene. F8 is the only gene in which mutations are known to cause hemophilia A. Clinical testing Targeted mutation analysis An F8 intron 22-A inversion is identified in nearly half of families with severe hemophilia A [Kaufman et al 2006]. This inversion can be detected by Southern blotting or, more recently, by long-range PCR [Bagnall et al 2006] or inverse PCR [Rossetti et al 2008]. An F8 intron 1 inversion is identified in 2%-3% of individuals with severe hemophilia A. This inversion is typically detected by PCR [Bagnall et al 2002]. Sequence analysis The mutation detection rate in individuals with hemophilia A who do not have one of the two common inversions varies from 75% to 98%, depending on the testing methods used. In severe hemophilia A, gross gene alterations (including large deletions or insertions, frameshift and splice junction changes, and nonsense and missense mutations) of F8 account for approximately 50% of mutations detected [Kemball-Cook et al 1998, El-Maarri et al 2005, Kaufman et al 2006]. In mild to moderate hemophilia A, missense mutations within the exons coding for the three A domains or the two C domains account for most of the mutations detected [Kemball-Cook et al 1998, Kaufman et al 2006]. Deletion/duplication analysisIn affected males deletion/duplication analysis can confirm the present of exonic, multiexonic, or larger deletions suspected on sequence analysis. In carrier females deletion/duplication analysis can detect gene deletions and rearrangements not detectable by sequence analysis [Santacroce et al 2009]. Guidelines for laboratory practice for molecular analysis of F8 have been established in the UK [Keeney et al 2005 (click for full text)]. Table 1. Summary of Molecular Genetic Testing Used in Hemophilia AView in own windowGene SymbolTest MethodMutations DetectedMutation Detection Frequency by Test Method 1Test AvailabilitySevere Hemophilia AModerate or Mild Hemophilia AAffected MalesCarrier FemalesAffected MalesCarrier FemalesF8Targeted mutation analysisIntron 22-A inversion 248% 348% 30% 30% 3ClinicalIntron 1 inversion2-3% 42-3% 40% 40% 4Sequence analysis / mutation scanning 5Sequence variants 649% 7,843% 876%-99% 7,876%-98% 9Deletion / duplication analysis 10Deletion / duplication of one or more exons or the whole gene 6%6%<1%<1%1. The ability of the test method used to detect a mutation that is present in the indicated gene2. Intron 22 inversions can be accompanied by adjacent partial-gene deletions or duplication/insertions [Andrikovics et al 2003].3. An intron 22-A inversion is identified in nearly half of families with severe hemophilia A [Kaufman et al 2006] and not identified in families with moderate or mild hemophilia A. Note: An uncommon exception occurs when severe hemophilia A is misdiagnosed as moderate hemophilia A, given the phenotypic variability among persons with null mutations. 4. An intron 1 inversion is identified in 2%-3% of individuals with severe hemophilia A [Bagnall et al 2002] and has not been described in families with moderate or mild hemophilia A. 5. Sequence analysis and mutation scanning of the entire gene can have similar detection frequencies; however, detection rates for mutation scanning may vary considerably among laboratories based on specific protocol used.6. Examples of mutations detected by sequence analysis may include small intragenic deletions/insertions and missense, nonsense, and splice site mutations.7. Lack of amplification by PCRs prior to sequence analysis suggests a deletion of one or more exons or the entire X-linked gene in a male; confirmation may require additional testing by using alternative amplification primers or deletion/duplication analysis. 8. Includes the mutation detection frequency using deletion/duplication analysis.9. Sequence analysis of genomic DNA cannot detect deletion or duplication of one or more exons or the entire X-linked gene in a heterozygous female.10. Testing that identifies deletions/duplications not readily detectable by sequence analysis of the coding and flanking intronic regions of genomic DNA; a variety of methods including quantitative PCR, long-range PCR, multiplex ligation-dependent probe amplification (MLPA), or targeted array GH (gene/segment-specific) may be used. A full array GH analysis that detects deletions/duplications across the genome may also include this gene/segment. Interpretation of test results. For issues to consider in interpretation of sequence analysis results, click here.Linkage analysis is used to track an unidentified F8 disease-causing allele in a family and to identify the origin of de novo mutations: Tracking an unidentified F8 mutation. When a disease-causing mutation of F8 is not identified in an affected family member by direct DNA testing, linkage analysis can be considered to obtain information for genetic counseling in families in which more than one family member has the unequivocal diagnosis of hemophilia A. Linkage studies are always based on accurate clinical diagnosis of hemophilia A in the affected family members and accurate understanding of the genetic relationships in the family. In addition, linkage analysis depends on the availability and willingness of family members to be tested and on the presence of informative heterozygous polymorphic markers. Use of up to five intragenic variants and one extragenic variant is informative in approximately 80%-90% of families. Recombination events between F8 and the extragenic site occur in up to 5% of meioses, but have not been observed between hemophilia-causing mutations and intragenic sites. Identifying the origin of a de novo mutation. Among the nearly 50% of families with a simplex case of hemophilia A (i.e., occurrence in one family member only), the origin of a de novo mutation can often be identified by performing molecular genetic testing in conjunction with linkage analysis. The presence of the mutation on the affected individual's factor VIII haplotype is tracked back through the parents and, if necessary, through maternal grandparents to identify the individual in whom the mutation originated. Testing StrategyTo confirm/establish the diagnosis of hemophilia A in a proband requires measurement of factor VIII clotting activity. Molecular genetic testing is performed on a proband to detect the family-specific mutation in F8 in order to obtain information for genetic counseling of at-risk family members. If an affected individual is not available, an obligate carrier female can be tested. In an individual who represents a simplex case, identification of the specific F8 mutation can help predict the clinical phenotype and assess the risk of developing a factor VIII inhibitor. For (a) individuals with severe hemophilia A, (b) females with a family history of severe hemophilia A, or (c) females with a family history of hemophilia A of unknown severity in whom the family-specific mutation is not known, molecular genetic testing is generally performed in the following sequence until a mutation (or linkage) is identified: Targeted mutation analysis to identify the intron 22 or intron 1 inversionSequence analysis of the 26 exons in F8 Deletion/duplication analysis Linkage analysisFor (a) individuals with moderate or mild hemophilia A or (b) females with a family history of moderate or mild hemophilia A in whom the family-specific mutation is not known, molecular genetic testing is generally performed in the following sequence until a mutation is identified: Sequence analysis of F8 Deletion/duplication analysis Linkage analysisNote: When carrier testing is performed without previous identification of the F8 mutation in the family, a negative result in an at-risk relative is not informative. Carrier testing for at-risk relatives is most informative after identification of the disease-causing mutation in the family. See above for testing of at-risk females when the family-specific mutation is not known.Note: Carriers are heterozygotes for an X-linked disorder and may develop clinical findings related to the disorder.Prenatal diagnosis and preimplantation genetic diagnosis (PGD) for at-risk pregnancies require prior identification of the disease-causing mutations in the family. Genetically Related (Allelic) DisordersNo other phenotypes are associated with mutations in F8.
Hemophilia A in the untreated individual is characterized by delayed bleeding or prolonged oozing after injuries, tooth extractions, or surgery, or renewed bleeding after initial bleeding has stopped [Kessler & Mariani 2006]. Muscle hematomas or intracranial bleeding can occur four or five days after the original injury. Intermittent oozing may last for days or weeks after tooth extraction. Prolonged or delayed bleeding or wound hematoma formation after surgery is common. After circumcision, males with hemophilia A of any severity may have prolonged oozing; but they can also heal normally without treatment. In severe hemophilia A, spontaneous joint bleeding is the most frequent symptom. ...
Natural HistoryHemophilia A in the untreated individual is characterized by delayed bleeding or prolonged oozing after injuries, tooth extractions, or surgery, or renewed bleeding after initial bleeding has stopped [Kessler & Mariani 2006]. Muscle hematomas or intracranial bleeding can occur four or five days after the original injury. Intermittent oozing may last for days or weeks after tooth extraction. Prolonged or delayed bleeding or wound hematoma formation after surgery is common. After circumcision, males with hemophilia A of any severity may have prolonged oozing; but they can also heal normally without treatment. In severe hemophilia A, spontaneous joint bleeding is the most frequent symptom. The age of diagnosis and frequency of bleeding episodes in the untreated individual are related to the factor VIII clotting activity (see Table 2). In any affected individual, bleeding episodes may be more frequent in childhood and adolescence than in adulthood. To some extent, this greater frequency is a function of both physical activity levels and vulnerability during more rapid growth. Individuals with severe hemophilia A are usually diagnosed during the first year of life. On rare occasions, infants with severe hemophilia A have extra- or intracranial bleeding following birth. In untreated toddlers, bleeding from minor mouth injuries and large "goose eggs" from minor head bumps are common and are the most frequent presenting symptoms of severe hemophilia A. Intracranial bleeding may also result from head injuries. The untreated child almost always has subcutaneous hematomas; some have been referred for evaluation of possible non-accidental trauma. As the child grows and becomes more active, spontaneous joint bleeds occur with increasing frequency unless the child is on a prophylactic treatment program. Spontaneous joint bleeds or deep-muscle hematomas initially cause pain or limping before swelling appears. Children and adults with severe hemophilia A who are not treated have an average of two to five spontaneous bleeding episodes each month. Joints are the most common sites of spontaneous bleeding, but other sites include the kidneys, gastrointestinal tract, and brain. Without prophylactic treatment, individuals with hemophilia A have prolonged bleeding or excessive pain and swelling from minor injuries, surgery, and tooth extractions. Individuals with moderate hemophilia A seldom have spontaneous bleeding but bleeding episodes may be precipitated by relatively minor trauma. Without pretreatment (as for elective invasive procedures) they do have prolonged or delayed oozing after relatively minor trauma and are usually diagnosed before age five to six years. The frequency of bleeding episodes requiring treatment with factor VIII concentrates varies from once a month to once a year. Signs and symptoms of bleeding are otherwise similar to those found in severe hemophilia A. Individuals with mild hemophilia A do not have spontaneous bleeding. However, without treatment abnormal bleeding occurs with surgery, tooth extractions, and major injuries. The frequency of bleeding may vary from once a year to once every ten years. Individuals with mild hemophilia A are often not diagnosed until later in life when they undergo surgery or tooth extraction or experience major trauma. Carrier females with a factor VIII clotting activity level lower than 35% are at risk for bleeding that is usually comparable to that seen in males with mild hemophilia. However, more subtle abnormal bleeding may occur with a baseline factor VIII clotting activity between 35% and 60% [Plug et al 2006]. Table 2. Symptoms Related to Severity of Untreated Hemophilia AView in own windowSeverity Factor VIII Clotting Activity 1 Symptoms Usual Age of Diagnosis Severe <1% Frequent spontaneous bleeding; abnormal bleeding after minor injuries, surgery, or tooth extractions Age ≤2 years 2 Moderately severe 1%-5% Spontaneous bleeding is rare; abnormal bleeding after minor injuries, surgery, or tooth extractions Age <5-6 years Mild >5%-35% No spontaneous bleeding; abnormal bleeding after major injuries, surgery, or tooth extractions Often later in life, depending on hemostatic challenges 1. Clinical severity does not always correlate with the in vitro assay result.2. Kulkarni et al [2009]Complications of untreated bleeding. The leading cause of death related to bleeding is intracranial hemorrhage. The major cause of disability from bleeding is chronic joint disease [Luck et al 2004]. Currently available treatment with clotting factor concentrates is normalizing life expectancy and reducing chronic joint disease for children with hemophilia A. Prior to the availability of such treatment, the median life expectancy for individuals with severe hemophilia A was 11 years (the current life expectancy for affected individuals in several developing countries). Excluding death from HIV, life expectancy for those severely affected individuals receiving adequate treatment is 63 years [Darby et al 2007]. Other. Since the mid-1960s, the mainstay of treatment of bleeding episodes has been factor VIII concentrates that initially were derived solely from donor plasma. Viral inactivation methods and donor screening of plasmas were introduced by the mid-1980s and recombinant factor VIII concentrates were introduced in the early 1990s, essentially ending the risk of HIV transmission. Many individuals who received plasma-derived factor VIII concentrates from 1979 to 1985 contracted HIV. Approximately half of these individuals died of AIDS prior to the advent of effective HIV therapy. Hepatitis B transmission from earlier plasma-derived concentrates was eliminated with donor screening and then vaccination in the 1970s. Most individuals exposed to plasma-derived concentrates prior to the late 1980s became chronic carriers of the hepatitis C virus. Viral inactivation methods implemented in concentrate preparation and donor screening assays developed by 1990 have essentially eliminated this complication. Approximately 30% of individuals with severe hemophilia A develop alloimmune inhibitors to factor VIII, usually within the first 20 exposures to infused factor VIII [Hay et al 2011] and, infrequently, in those who have received more than 50 exposures [Kempton 2010] (see Management, Treatment of Manifestations). Among individuals with hemophilia A, more blacks than whites develop the inhibitors, possibly as a result of differences in F8 haplotypes [Viel et al 2009].
Genotype-Phenotype CorrelationsDisease severityF8 inversions are associated with severe hemophilia A and account for 45% of the severe cases [Kaufman et al 2006]. Of these, 20% to 30% develop alloimmune inhibitors. Occasionally, individuals considered to have moderate hemophilia A have been found to have F8 inversions. Often their assays have contained either some residual factor VIII clotting activity from a prior transfusion or the assay methods used were inaccurate at low levels. An inversion between a 1-kb sequence in intron 1 and an inverted repeat 5' to F8 [Bagnall et al 2002] is also associated with a severe phenotype, and some individuals have developed inhibitors. Point mutations leading to new stop codons are essentially all associated with a severe phenotype, as are most frameshift mutations. (An exception is the insertion or deletion of adenosine bases resulting in a sequence of eight to ten adenosines, which may result in moderate hemophilia A [Nakaya et al 2001].)Splice site mutations are often severe but may be mild, depending on the specific change and location. Missense mutations occur in fewer than 20% of individuals with severe hemophilia A but nearly all of those with mild or moderately severe bleeding A single base change in the 5’ promoter region of F8 has been associated with mild hemophilia A [Riccardi et al 2009].
When an individual presents with bleeding or the history of being a "bleeder," the first task is to determine if he/she truly has abnormal bleeding. "Bleeding a lot" during or immediately after major trauma, after a tonsillectomy, or for a few hours following tooth extraction may not be significant. In contrast, prolonged or intermittent oozing that lasts several days following tooth extraction or mouth injury, renewed bleeding or increased pain and swelling several days after an injury, or developing a wound hematoma several days after surgery almost always indicates a coagulation problem. A detailed history of bleeding episodes can help determine if the individual has a lifelong, inherited bleeding disorder or an acquired (often transient) bleeding disorder. ...
Differential DiagnosisWhen an individual presents with bleeding or the history of being a "bleeder," the first task is to determine if he/she truly has abnormal bleeding. "Bleeding a lot" during or immediately after major trauma, after a tonsillectomy, or for a few hours following tooth extraction may not be significant. In contrast, prolonged or intermittent oozing that lasts several days following tooth extraction or mouth injury, renewed bleeding or increased pain and swelling several days after an injury, or developing a wound hematoma several days after surgery almost always indicates a coagulation problem. A detailed history of bleeding episodes can help determine if the individual has a lifelong, inherited bleeding disorder or an acquired (often transient) bleeding disorder. Physical examination provides few specific diagnostic clues. An older individual with severe or moderate hemophilia A may have joint deformities and muscle contractures. Large bruises and subcutaneous hematomas for which no trauma can be identified may be present, but individuals with a mild bleeding disorder have no outward signs except during an acute bleeding episode. Petechial hemorrhages indicate severe thrombocytopenia and are not a feature of hemophilia A. A family history with a pattern of autosomal dominant, autosomal recessive, or X-linked inheritance provides clues to the diagnosis of the bleeding disorder but is not definitive. Hemophilia A and hemophilia B are both inherited in an X-linked manner. De novo F8 mutations occur and their origin can be documented in up to half of the families with newly diagnosed, affected members. Some families with mild hemophilia A are mistakenly diagnosed as having von Willebrand disease because both men and women have abnormal bleeding. With improved testing for von Willebrand disease, it is now possible to determine that women in such families often do not have von Willebrand disease, but rather are symptomatic carriers of hemophilia A.Hemophilia A is only one of several lifelong bleeding disorders, and coagulation factor assays are the main tools for determining the specific diagnosis. Other inherited bleeding disorders associated with a low factor VIII clotting activity include the following:Mild (type 1) von Willebrand disease (VWD) accounts for 80% of individuals with VWD and is characterized by a quantitative deficiency of von Willebrand factor (low VWF antigen, factor VIII clotting activity, and ristocetin cofactor activity). Mucous membrane bleeding and prolonged oozing after surgery or tooth extractions are the predominant symptoms; laboratory testing is needed to differentiate mild hemophilia from VWD. Essentially all individuals with hemophilia A have a normal VWF level. Inheritance of VWD is autosomal dominant; penetrance varies. Type 2A or 2B VWD is characterized by a qualitative deficiency of VWF with a decrease of the high molecular weight multimers. VWF antigen and factor VIII clotting activity may be low-normal to mildly decreased. Functional VWF level is low in a ristocetin cofactor assay. Inheritance is autosomal dominant. Type 2B VWD is caused by a gain of function in platelet binding and is often accompanied by thrombocytopenia. Molecular genetic testing can aid in diagnosis.Type 2M VWD is also characterized by a qualitative deficiency of VWF with a similar gain of function in platelet binding as with type 2B; however, it is associated with a normal multimer pattern. Inheritance is autosomal dominant. Molecular genetic testing can aid in the diagnosis and distinction of subtypes of VWD type 2.Type 2N VWD is an uncommon variant caused by one of several missense mutations in the amino terminus of the circulating VWF protein, resulting in defective binding of factor VIII to VWF. Platelet function is completely normal. Clinically and biochemically, type 2N VWD is indistinguishable from mild hemophilia A; however, mild hemophilia A can be distinguished from type 2N VWD by molecular genetic testing of F8, molecular genetic testing of VWF, or measuring binding of factor VIII to VWF using ELISA or column chromatography. The low factor VIII clotting activity usually shows autosomal recessive inheritance. Severe, type 3 VWD is characterized by frequent episodes of mucous membrane bleeding and joint and muscle bleeding similar to that seen in individuals with hemophilia A. The VWF level is lower than 1% and the factor VIII clotting activity is 2%-8%. Inheritance is autosomal recessive. Parents may have type 1 VWD but more often are asymptomatic. Mild combined factor V and factor VIII deficiencies are usually caused by rare autosomal recessive inheritance of a deficiency of one of two intracellular chaperone proteins encoded by LMAN1 or MCFD2 [Zhang et al 2008]. The following are other bleeding disorders with normal factor VIII clotting activity: Hemophilia B is clinically indistinguishable from hemophilia A. Diagnosis is based on a factor IX clotting activity lower than 30%. Inheritance is X-linked. Factor XI deficiency is inherited in an autosomal recessive manner with heterozygotes showing a factor XI coagulant activity of 25% to 75% of normal, while homozygotes have activity of lower than 1% to 15% [Thompson 2006]. Two mutations are common among individuals of Ashkenazi Jewish descent. Both compound heterozygotes and homozygotes may exhibit bleeding similar to that seen in mild or moderate hemophilia A. A specific factor XI clotting assay establishes the diagnosis. Factor XII, prekallekrein, or high molecular weight kininogen deficiencies do not cause clinical bleeding but can cause a long activated partial thromboplastin time (APTT). Prothrombin (factor II), factor V, factor X, and factor VII deficiencies are rare bleeding disorders inherited in an autosomal recessive manner [Thompson 2006]. Individuals may display easy bruising and hematoma formation, epistaxis, menorrhagia, and bleeding after trauma and surgery. Hemarthroses are uncommon. Spontaneous intracranial bleeding can occur. Factor VII deficiency should be suspected if the PT is prolonged and APTT normal. Individuals with deficiency of factors II, V, or X usually have prolonged PT and APTT, but specific coagulation factor assays establish the diagnosis. Combined (multiple) deficiencies are usually acquired disorders, although a few families have hereditary deficits of the vitamin K-dependent factors, often resulting from deficiency of gamma-carboxylase. Fibrinogen disorders can be severe, mild, or asymptomatic [Thompson 2006]: Congenital afibrinogenemia is a rare disorder inherited in an autosomal recessive manner with manifestations similar to hemophilia A except that bleeding from minor cuts is prolonged because of the lack of fibrinogen to support platelet aggregation. Hypofibrinogenemia can be inherited either in an autosomal dominant or autosomal recessive manner and is usually asymptomatic but may be combined with dysfibrinogenemia. Dysfibrinogenemia is inherited in an autosomal dominant manner. Individuals with hypofibrinogenemia or dysfibrinogenemia have mild to moderate bleeding symptoms or may be asymptomatic; some individuals with dysfibrinogenemia are at risk for thrombosis. Diagnosis is based on kinetic being lower than antigenic protein levels, although the thrombin time is usually prolonged and is a simple screening test. Factor XIII deficiency is a rare autosomal recessive disorder [Thompson 2006]. Umbilical stump bleeding occurs in more than 80% of individuals. Intracranial bleeding that occurs spontaneously or following minor trauma is seen in 30% of individuals. Subcutaneous hematomas, muscle hematomas, defective wound healing, and recurrent spontaneous abortion are also seen. Joint bleeding is rare. All kinetic coagulation screening tests are normal; a specific test for clot solubility must be performed. Platelet function disorders cause bleeding problems similar to those seen in individuals with thrombocytopenia. Individuals have skin and mucous membrane bleeding, recurring epistaxis, gastrointestinal bleeding, menorrhagia, and excessive bleeding during or immediately after trauma and surgery. Joint, muscle, and intracranial bleeding is rare. Diagnosis is made utilizing platelet aggregation assays and flow cytometry.Bernard-Soulier syndrome is inherited in an autosomal recessive manner and involves the VWF receptor, the platelet membrane GPIb-IX complex. Glanzmann's thrombasthenia, also autosomal recessive, involves the GPIIb-IIIa receptor necessary for platelet aggregation. Abnormal platelet function is usually associated with a prolonged bleeding time or prolonged closure time on platelet function analysis. Note to clinicians: For a patient-specific ‘simultaneous consult’ related to this disorder, go to , an interactive diagnostic decision support software tool that provides differential diagnoses based on patient findings (registration or institutional access required).Hemophilia A: malesHemophilia A: female heterozygotes
To establish the extent of disease in an individual diagnosed with hemophilia A, the following evaluations are recommended:...
ManagementEvaluations Following Initial DiagnosisTo establish the extent of disease in an individual diagnosed with hemophilia A, the following evaluations are recommended:Identification of the specific F8 disease-causing mutation in an individual to aid in determining disease severity, the likelihood of inhibitor development, and the chance that immune tolerance will be successful if an inhibitor does develop A personal and family history of bleeding to help predict disease severity A joint and muscle evaluation, particularly if the individual describes a history of hemarthrosis or deep-muscle hematomas Screening for hepatitis A, B, and C, as well as HIV, particularly if blood products or plasma-derived clotting factor concentrates were administered prior to 1985 Baseline CBC and platelet count, especially if there is a history of nose bleeds, GI bleeding, mouth bleeding; or in women, menorrhagia or postpartum hemorrhageTreatment of ManifestationsIn developed countries, life expectancy for individuals with hemophilia A has greatly increased over the past four decades [Darby et al 2007]; disability has decreased with the intravenous infusion of factor VIII concentrate, home infusion programs, prophylactic treatment, and improved patient education. Individuals with hemophilia A benefit from referral for assessment, education, and genetic counseling at one of the approximately 140 federally funded hemophilia treatment centers (HTCs) in the USA that can be located through the National Hemophilia Foundation. Worldwide, treatment centers can be found through the World Federation of Haemophilia. The treatment centers establish appropriate treatment plans and provide referrals or direct care for individuals with inherited bleeding disorders. They also are a resource for current information on new treatment modalities for hemophilia. An assessment at one of these centers usually includes extensive patient education, genetic counseling, and laboratory testing. Intravenous infusion of factor VIII concentrate. Recombinant factor VIII concentrates have been available for more than 15 years; some recombinant products now contain no human- or animal-derived proteins. Virucidal treatment of plasma-derived concentrates has eliminated the risk of HIV transmission since 1985, and of hepatitis B and C viruses since 1990. Bleeding episodes are prevented or controlled quickly with intravenous infusions of either plasma-derived or recombinant factor VIII concentrate. Fast, effective treatment of bleeding episodes decreases pain and disability and reduces the risk of chronic joint disease. Ideally, the affected individual should receive clotting factor within an hour of noticing symptoms [Kessler & Mariani 2006]. Doses vary among individuals, but knowledge of a single in vivo recovery value does not always help in determining the appropriate dose [Bjorkman et al 2007]:Arranging efficient, effective treatment for infants and toddlers is especially challenging. Because frequent venipunctures may be necessary, it is important to identify staff members who are expert in performing venipunctures in small children. It is recommended that the parents of children age two to five years with severe hemophilia A be trained to administer the infusions as soon as it is feasible. Home treatment allows for prompt treatment after symptoms occur and facilitates prophylactic therapy. DDAVP (1-deamino-8-D-arginine vasopressin). For many individuals with mild hemophilia A, including most symptomatic carriers, immediate treatment of bleeding or prophylaxis can be achieved with desmopressin (DDAVP) [Castaman et al 2009]. A single intravenous dose often doubles or triples factor VIII clotting activity. Alternatively, a multi-use, nasal formulation of desmopressin (Stimate®) is more convenient and available. Pediatric issues. Special considerations for care of infants and children with hemophilia A include the following [Chalmers et al 2005]: Infant males with a family history of hemophilia A should not be circumcised unless hemophilia A is either excluded or, if present, is treated with factor VIII concentrate directly before and after the procedure to prevent delayed oozing and poor wound healing. Intramuscular injections should be avoided; immunizations should be administered subcutaneously. Effective dosing of factor VIII requires an understanding of different pharmacokinetics in young children. Inhibitors. Alloimmune inhibitors to factor VIII greatly compromise the ability to manage bleeding episodes [Hay et al 2006, Kessler & Mariani 2006]. High titer inhibitors can often be eliminated by immune tolerance therapy. Individuals with large gene deletions are less likely to respond to immune tolerance than individuals with other types of mutations [Peyvandi et al 2006, Coppola et al 2009]. Prevention of Primary ManifestationsChildren with severe hemophilia A are often given "primary" prophylactic infusions of factor VIII concentrate three times a week or every other day to maintain factor VIII clotting activity above 1%; these infusions prevent spontaneous bleeding and decrease the number of bleeding episodes. Prophylactic infusions almost completely eliminate joint bleeding and greatly decrease chronic joint disease. Prevention of Secondary ComplicationsPrevention of chronic joint disease is a major concern. It is agreed that most individuals with severe hemophilia A benefit from primary prophylaxis, but controversy still exists about when these regular infusions should begin. The age at which a child experiences the first joint bleed can vary greatly. Prophylactic infusions almost completely eliminate spontaneous joint bleeding, decreasing chronic joint disease, although complications of venous access ports in young children can occur [Feldman et al 2006, Manco-Johnson et al 2007]. "Secondary" prophylaxis is often used for several weeks if recurrent bleeding in a "target" joint or synovitis occurs, or for longer periods in adults with frequent bleeding. SurveillancePersons with hemophilia who are followed at hemophilia treatment centers (HTCs) (see Resources) have lower mortality than those who are not [Soucie et al 2000]. It is recommended that young children with severe or moderate hemophilia A have assessments at an HTC (accompanied by their parents) every six to 12 months to review their history of bleeding episodes and to adjust treatment plans as needed. Early signs and symptoms of possible bleeding episodes are reviewed. The assessment should also include a joint and muscle evaluation, an inhibitor screen, viral testing if indicated, and a discussion of any other problems related to the individual's hemophilia and family and community support.Screening for alloimmune inhibitors is usually done in individuals with severe hemophilia A every three to six months after treatment with factor VIII concentrates has been initiated either for bleeding or prophylaxis. After 50 to 100 exposure days, annual screening is sufficient; in adults, it is usually performed only prior to any elective surgery. Testing for inhibitors should also be performed in any individual with hemophilia whenever a sub-optimal clinical response to treatment is suspected, regardless of disease severity.Older children and adults with severe or moderate hemophilia A benefit from regular contact with an HTC (see Resources) and periodic assessments to review bleeding episodes and treatment plans, evaluate joints and muscles, screen for an inhibitor, perform viral testing if indicated, provide education, and discuss other issues relevant to the individual's hemophilia.Individuals with mild hemophilia A can benefit from maintaining a relationship with an HTC and having regular assessments every two to three years.Agents/Circumstances to AvoidAvoid the following:Activities that involve a high risk of trauma, particularly head injury Aspirin and all aspirin-containing products Cautious use of other medications and herbal remedies that affect platelet function is indicated. Evaluation of Relatives at RiskIdentification of at-risk relatives. A thorough family history may identify other male relatives who are at risk but have not been tested (particularly in families with mild hemophilia A). Early determination of the genetic status of males at risk. Either assay of factor VIII clotting activity from a cord blood sample obtained by venipuncture of the umbilical vein (to avoid contamination by amniotic fluid or placenta tissue) or molecular genetic testing for the family-specific F8 mutation can establish or exclude the diagnosis of hemophilia A in newborn males at risk. Infants with a family history of hemophilia A should not be circumcised unless hemophilia A is either excluded or, if present, factor VIII concentrate is administered immediately before and after the procedure to prevent delayed oozing and poor wound healing. Note: The cord blood for factor VIII clotting activity assay should be drawn into a syringe containing one-tenth volume of sodium citrate to avoid clotting and to provide an optimal mixing of the sample with the anticoagulant.Determination of genetic status of females at risk. Approximately 10% of carriers have factor VIII activity lower than 30%-35% and may have abnormal bleeding themselves. In a survey of Dutch hemophilia carriers, bleeding symptoms correlated with baseline factor clotting activity; there was suggestion of a very mild increase in bleeding even in those with 40% to 60% factor VIII activity [Plug et al 2006]. Therefore, all daughters and mothers of an affected male and other at-risk females should have a baseline factor VIII clotting activity assay to determine if they are at increased risk for bleeding (unless they are known to be non-carriers based on molecular genetic testing). Very occasionally, a woman will have particularly low factor VIII clotting activity that may result from heterozygosity for an F8 mutation associated with skewed X-chromosome inactivation or, on rare occasion, compound heterozygosity for two F8 mutations [Pavlova et al 2009].It is recommended that the carrier status of a woman at risk be established prior to pregnancy or as early in a pregnancy as possible.See Genetic Counseling for issues related to testing of at-risk relatives for genetic counseling purposes.Pregnancy Management Obstetric issues. It is recommended that the carrier status of a woman at risk be established prior to pregnancy or as early in a pregnancy as possible. If the mother is a symptomatic carrier (i.e., has baseline factor VIII clotting activity <35%), she will be somewhat protected by the natural rise of factor VIII clotting activity during pregnancy, which may even double by the end of the third trimester. However, postpartum factor VIII clotting activity can return to baseline within 48 hours, and delayed bleeding may ensue [Lee et al 2006].Newborn males. Controversy remains as to indications for Cesarean section versus vaginal delivery [James & Hoots 2010, Ljung 2010]. For elective deliveries, the relative risks of Cesarean section versus vaginal delivery should be considered, especially if a male has been diagnosed with hemophilia A prenatally. At birth or in the early neonatal period, intracranial hemorrhage in affected males is uncommon (1%-2%), even in males with severe hemophilia A who are delivered vaginally. Therapies Under InvestigationLonger-acting factor VIII concentrates are undergoing clinical trials. The hope is that one infusion a week rather than three to four infusions a week will provide prophylaxis against spontaneous bleeding [Spira et al 2010]. Attempts are being made to learn more about the immunology of inhibitors and ways to prevent them or improve the success rate of immune tolerance [Lollar 2006, Zakarija et al 2011]. All clinical trials for gene therapy in hemophilia A have been discontinued because of complications and failure to achieve significant factor VIII expression in humans with hemophilia A. Although the hemophilia community remains hopeful, several obstacles must be overcome before new trials can begin with factor VIII [Pierce et al 2007]. Search ClinicalTrials.gov for access to information on clinical studies for a wide range of diseases and conditions.OtherVitamin K does not prevent or control bleeding in hemophilia A. Cryoprecipitate is no longer recommended to treat hemophilia A because it is not treated with a virucidal agent.
Information in the Molecular Genetics and OMIM tables may differ from that elsewhere in the GeneReview: tables may contain more recent information. —ED....
Molecular GeneticsInformation in the Molecular Genetics and OMIM tables may differ from that elsewhere in the GeneReview: tables may contain more recent information. —ED.Table A. Hemophilia A: Genes and DatabasesView in own windowGene SymbolChromosomal LocusProtein NameLocus SpecificHGMDF8Xq28Coagulation factor VIIIHemobase: Hemophilia A mutation registry F8 @ LOVD Haemophilia A Mutation, Structure, Test & Resource Site (HAMSTeRS)F8Data are compiled from the following standard references: gene symbol from HGNC; chromosomal locus, locus name, critical region, complementation group from OMIM; protein name from UniProt. For a description of databases (Locus Specific, HGMD) to which links are provided, click here.Table B. OMIM Entries for Hemophilia A (View All in OMIM) View in own window 306700HEMOPHILIA A; HEMAMolecular Genetic Pathogenesis Normal allelic variants. F8 spans 186 kb and comprises 26 exons [Thompson 2003]. Normal variants are uncommon in the factor VIII transcript (Table 3). Normal allelic variants (and their dbSNP identifier) that are useful for linkage analysis include: a BclI restriction site in intron 18 (rs4898352), a single-base change in intron 7 (only informative if BclI is homozygous for the non-cleaved or less common allele, rs7058826), an XbaI site in intron 22, a BglI site in intron 25 (rs1509787), an A/G dimorphism at a MseI site in the 3' untranslated portion of exon 26 at base 8899 (rs1050705), and two series of CA repeat polymorphisms in introns 13 and 22. Only two coding sequence variants are frequently polymorphic in whites, c.3780C>G (rs1800291) and c.3864A>C (rs1800292), both in exon 14 (Table 3). In African Americans, the normal variant c.6771G in exon 25 is the most common allele, whereas essentially all individuals of northern European ancestry have the F8 variant c.6771A. These variants code for Val or Met, respectively, at amino acid 2257 [Viel et al 2007].Table 3. Selected F8 Normal Allelic Variants View in own windowDNA Nucleotide Change (Alias 1, 2)Protein Amino Acid Change (Alias 1, 3)Reference Sequencec.3780C>G (3951C>G)p.Asp1260Glu (Asp1241Glu)NM_000132.2 NP_000123.1 c.3864A>C (4035A>C)p.Ser1288 (Ser1269)c.6771A>G (6940A>G)p.Met2257Val (Met2238Val)c.*8899A>G 4 --See Quick Reference for an explanation of nomenclature. GeneReviews follows the standard naming conventions of the Human Genome Variation Society (www.hgvs.org). 1. Variant designation that does not conform to current naming conventions 2. DNA nucleotide aliases are numbered from the first nucleotide of the reference sequence NM_000132.2, which has 171 bases prior to the initial ATG codon for Met.3. Protein amino acid aliases are numbered from the first residue of the mature protein, in contrast to the convention of numbering from the first initiating methionine codon, which in the case of F8 is the beginning of the 19-amino acid signal sequence.4. The asterisk indicates that the nucleotide change is in the 3' untranslated region of the gene.Pathologic allelic variants. Gene inversions account for approximately 45% of the F8 mutations in severe hemophilia A [Kaufman et al 2006]. F8 inversions usually occur through recombination between a sequence located within intron 22 with one of two additional copies of homologous sequence that are located 400-500 kb 5’ from F8 (about half the distance to the telomere of the long arm of the X chromosome) [Bagnall et al 2006]. Of the two most frequent types, cross-over with the distal telomeric sequence (designated as int22h3) is more frequent than with the proximal sequence (designated as int22h2, which appears to require a separate inversion first in order to be in the opposite direction of the intron 22 sequence to align for mis-pairing). Infrequently, a third telomeric copy can be present and can lead to a variant intron 22 inversion pattern on Southern blotting; alternative patterns can also be seen when the inversion is accompanied by large partial-gene deletions or duplication-insertion events [Andrikovics et al 2003]. A different recurrent inversion occurs between a 1-kb sequence in intron 1 (designated int1h-1) that is repeated in the reverse orientation (designated int1h-2), approximately 140 kb 5' (telomeric) to F8 [Bagnall et al 2002]; intron 1 inversions occur in up to 3% of families with severe hemophilia A. The remaining types of mutations span the entire spectrum including whole- or partial-gene deletions, large insertions, sequence duplications, small deletions or insertions (usually resulting in frameshifts), splice junction alterations, nonsense mutations, and missense mutations. These non-inversion mutations of F8 are cataloged (see Table A, Locus-Specific Databases). Normal gene product. Factor VIII is expressed with a 19-amino acid signal peptide; the mature protein has 2332 residues [Thompson 2003, Kaufman et al 2006]. Its domain structure from the amino terminus is "A1-A2-B-A3-C1-C2" and is homologous to clotting factor V. The three A domains are homologous with ceruloplasmin and the two C domains with discoidins. The known crystal structure of ceruloplasmin has allowed models of the A domains and localization of hemophilic missense mutations (see Table A, Locus-Specific Databases). High-resolution crystal structure of a recombinant human C2 domain is known, and hemophilic missense mutations have been localized to it and to a model of the homologous C1 domain [Liu et al 2000]. Crystal structures of activated factor VIII have been solved at just under four angstrom resolutions [Ngo et al 2008, Shen et al 2008]. Factor VIII is synthesized primarily in the liver and circulates as an inactive clotting cofactor that has been variably cleaved towards the carboxy terminus of the B domain prior to secretion. Concentration in plasma is just under 1 nmol/L (0.1 µg/mL). In the circulation, factor VIII is stabilized by binding to von Willebrand factor (VWF). Once activated by trace amounts of thrombin, it is released from VWF and binds to phospholipid membrane surfaces such as those provided by activated platelets. There it interacts with factor IXa to become the "intrinsic system" factor X activator [Stoilova-McPhie et al 2002]. Intrinsic factor X activation is a critical step in the early stages of coagulation. Abnormal gene product. Abnormal gene products vary from deficiency caused by absence of detectable protein (including the majority of individuals with severe hemophilia A) to those with normal levels of a dysfunctional protein. Some mutations are associated with comparably reduced levels of factor VIII clotting activity and antigen; where examined, these are caused by impaired secretion of factor VIII or instability of factor VIII in circulation. Certain premature termination codons, gene inversions, or gross gene alterations causing severe hemophilia A have an increased risk of being complicated by inhibitor development [Hay et al 2006, Peyvandi et al 2006, Salviato et al 2007, Coppola et al 2009, Astermark et al 2010].