DiagnosisClinical Diagnosis The clinical signs observed in microphthalmia with linear skin defects (MLS) syndrome are considered major if they are present in at least 80% of affected individuals and minor if they are less frequent. The clinical diagnosis of MLS syndrome can be made when the two major criteria are present [al-Gazali et al 1990, Happle et al 1993]; however, persons with a molecular diagnosis of MLS syndrome in whom only one of the two major criteria was present have been reported: some show characteristic skin defects without ocular abnormalities (see Figure 1); others show eye abnormalities without skin defects [Morleo & Franco 2008].FigureFigure 1. Reticulolinear scar lesions on the neck of a 36-year-old female with an otherwise normal phenotype. Cytogenetic analysis revealed 46,X,del(X)(p22.3 pter) [Lindsay et al 1994]. Minor criteria in the presence of a family history consistent with X-linked inheritance with male lethality support the clinical diagnosis of MLS syndrome.Major criteriaMicrophthalmia and/or anophthalmia (reported in 93% of affected individuals), which can be unilateral or bilateral (see Figure 2).Linear skin defects (reported in 95% of affected individuals), which are present at birth and usually involve the face and neck (see Figure 3), although the scalp and occasionally the upper trunk may be involved [Zvulunov et al 1998]. The lesions heal with age, leaving minimal residual scarring.FigureFigure 2. Bilateral microphthalmia and irregular linear skin areas involving the face and neck in a female infant with MLS who has a single nucleotide mutation in exon 6 of HCCS [Wimplinger et al 2006] FigureFigure 3. Typical linear skin lesions on the face and neck of a newborn female with MLS who has a deletion of exons 1-3 of HCCS [Morleo et al 2005, Wimplinger et al 2006] Minor criteria (in order of frequency)Other ocular abnormalities that are variable and can include: sclerocornea, orbital cysts, microcornea, eyelid fissures, corneal leukoma, iridocorneal adhesion (Peters anomaly), congenital glaucoma with total/peripheral anterior synechiae, aniridia, cataracts, a remnant of the anterior hyaloid artery, vitreous opacity, and hypopigmented areas of the retinal pigment epithelium [Kobayashi et al 1998, Cape et al 2004, Wimplinger et al 2006]Central nervous system involvement: agenesis of corpus callosum, anencephaly, microcephaly [Happle et al 1993], hydrocephalus, intellectual disability, and infantile seizuresDevelopmental delayCongenital heart defects: hypertrophic cardiomyopathy, oncocytic cardiomyopathy [Bird et al 1994], atrial and ventricular septal defects, supraventricular tachycardia, ventricular fibrillation, and other arrhythmias Short statureDiaphragmatic hernia Nail dystrophyPreauricular pits and hearing loss Genitourinary malformations: anterior or imperforate anus [al-Gazali et al 1990], bicornuate uterus, ambiguous genitalia, penile hypospadias in rare males with a 46,XX karyotype, and pseudotail [Alberry et al 2011] (see Testing) Testing Cytogenetic analysis can reveal chromosomal abnormalities involving the Xp22 region. Approximately 79% of female probands have chromosomal abnormalities that result in monosomy for Xp22. Eight males with MLS syndrome with an XX karyotype with detectable Y-chromosome material (e.g., translocation of Y chromosome material onto an X chromosome) have been described [Morleo et al 2005, Kapur et al 2008].Only one 46,XY male with a mosaic paracentric inversion of Xp: 46Y,inv(X)(p22.13~22.2 p22.32~22.33)[49]/46,XY[271]) has been reported; he died a few hours after birth [Kutsche et al 2002]. Molecular Genetic Testing Gene. HCCS, encoding the mitochondrial holocytochrome c-type synthase, is the only gene in which mutation is known to cause MLS syndrome.Clinical testingFISH analysis. FISH studies can be performed using BAC clones. FISH can reveal chromosomal abnormalities (interstitial deletion) not detected by routine chromosome analysis and/or can help define the boundaries of the rearranged regions in individuals with an X-chromosome abnormality. Morleo et al [2005] reported one affected individual with a high-resolution karyotype that showed an interstitial deletion spanning about 3.2 Mb of genomic DNA in Xp22.2. Sequence analysis of HCCS coding exons has identified single nucleotide mutations in three probands (c.589C>T (p.Arg197X); c.649C>T (p.Arg217Cys); c.475G>A (p.Glu159Lys) [Wimplinger et al 2006, Wimplinger et al 2007b]. Deletion/duplication analysis * allows for detection of deletions of one or more HCCS exons not readily detectable by cytogenetic analysis, FISH, or sequence analysis of genomic DNA. Depending on the method employed, this type of analysis can often detect smaller deletions and define their boundaries more precisely than can FISH analysis.
* Testing that detects deletions/duplications not readily detectable by sequence analysis of genomic DNA; a variety of methods including quantitative PCR, real-time PCR, multiplex ligation-dependent probe amplification (MLPA), or array GH may be used.X-chromosome inactivation studies. Skewed X-chromosome inactivation has been detected in 21 of the 22 individuals with MLS syndrome analyzed to date [Anguiano et al 2003, Wimplinger et al 2006, Cain et al 2007, Schluth et al 2007, Wimplinger et al 2007a, Wimplinger et al 2007b, Hobson et al 2009, Steichen-Gersdorf et al 2010, Alberry et al 2011]. In all individuals the abnormal X is inactive.
Note: This analysis can be performed on a peripheral blood specimen by analysis of the androgen receptor gene (AR) on the X chromosome.Table 1. Summary of Molecular Genetic Testing Used in Microphthalmia with Linear Skin Defects SyndromeView in own windowGene SymbolTest MethodMutations DetectedMutation Detection Frequency by Test Method ^{1Test AvailabilityHCCSCytogenetic and FISH analysesMonosomy of Xp22 region (>11 Mb) 2; 3.2-Mb interstitial deletion 377%ClinicalSequence analysis3 single-nucleotide mutations (c.589C>T, c.649C>T, c.475G>A) 4, 53 affected females Deletion/ duplication analysis 6Deletion of exons 1-32 affected sisters and their healthy motherX-chromosome inactivation studiesSkewed X-chromosome inactivationNA Clinical1. The ability of the test method used to detect a mutation that is present in the indicated gene2. Caused by deletions or unbalanced translocations3. Detected by FISH analysis4. Sequence analysis of genomic DNA cannot detect deletion of one or more exons or the entire X-linked gene in a heterozygous female.5. Lack of amplification by PCRs prior to sequence analysis can suggest a putative deletion of one or more exons or the entire X-linked gene in a male; confirmation may require additional testing by deletion/duplication analysis.6. 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. Failure to identify an abnormal karyotype or deletion of the MLS region does not rule out the diagnosis of MLS syndrome. Information on specific allelic variants may be available in Molecular Genetics (see Table A. Genes and Databases and/or Pathologic allelic variants).Testing Strategy To confirm/establish the diagnosis in a proband. To make a presumptive diagnosis, clinical evaluation, including the history of skin lesions and detailed family history, should be performed.To confirm the diagnosis, genetic tests are recommended in the following order: Cytogenetic analysis from peripheral blood lymphocytes to identify chromosomal rearrangements involving the Xp22 region. A karyotype should be considered in males with MLS syndrome to look for evidence of 46,XX karyotype or an X/Y translocation. X-chromosome inactivation studies on a blood sample to look for evidence of X-chromosome skewing. Note: X-chromosome inactivation studies on peripheral blood samples can be helpful in establishing the diagnosis of MLS syndrome in individuals with a normal karyotype. To date, totally skewed X-inactivation of the abnormal X-chromosome has been detected in 21 of the 22 individuals with MLS syndrome tested who had either an abnormal karyotype or an HCCS point mutation or deletion. Array GH in individuals with normal high-resolution karyotype, to detect possible interstitial deletions in the MLS syndrome minimal critical region in Xp22.2FISH analysis in individuals with normal high-resolution karyotype when aGH is not available. It is used to identify and define interstitial deletions. Sequencing of the HCCS coding region in individuals who meet diagnostic criteria but do not have cytogenetic abnormalities Note: Histologic examination of a skin biopsy does not necessarily lead to the diagnosis.Carrier testing for at-risk female relatives requires prior identification of the disease-causing mutation in the family member. Alternatively, finding skewed X-chromosome inactivation in DNA isolated from peripheral lymphocytes can be helpful in identifying carriers if a cytogenetic abnormality or an HCCS mutation could not be identified in the proband. The finding of skewed X-chromosome inactivation would be supportive, but not definitive, evidence that an at-risk relative is a carrier of MLS syndrome. Prenatal diagnosis and preimplantation genetic diagnosis (PGD) for at-risk pregnancies require prior identification of the disease-causing mutation in the family.Genetically Related (Allelic) DisordersIt is currently unknown if other disorders are allelic to MLS syndrome.}

Natural History Microphthalmia with linear skin defects (MLS) syndrome is characterized by unilateral or bilateral microphthalmia or anophthalmia (see Figure 2) and jagged skin defects on the face and neck (see Figure 3). MLS syndrome is usually lethal in males. Information is based on findings in the 56 affected individuals reported to date [Kono et al 1999, Kherbaoui-Redouani et al 2003, Wimplinger et al 2006, Wimplinger et al 2007a, Wimplinger et al 2007b, Kapur et al 2008, Sharma et al 2008, Hobson et al 2009, Steichen-Gersdorf et al 2010, Alberry et al 2011].Intra- and interfamilial phenotypic variability has been described. The manifestations vary among affected individuals and, although most display the classic phenotype of MLS syndrome, many have only a subset of characteristic features: some show the characteristic skin defects without ocular abnormalities, whereas others have eye abnormalities without skin defects [Morleo & Franco 2008]. An example is a female with a normal phenotype except for typical MLS syndrome skin defects (see Figure 1) who had an affected female fetus with anencephaly. Cytogenetic analysis revealed that mother and fetus had the same Xp22 deletion − one of the largest Xp deletions described for MLS syndrome [Lindsay et al 1994]. Skin manifestations. In general, no new lesions are observed after birth and the skin defects heal variably with age, leaving minimal residual scarring. The cutaneous findings typically follow the lines of Blaschko corresponding to cell migration pathways evident during embryonic and fetal skin development that, unlike dermatomes, do not correspond to innervation patterns. The restriction to the head and neck is thought to result from involvement of neural crest cells [al-Gazali et al 1990, Lindsay et al 1994]. Histologic findings. Happle et al [1993] coined the acronym MIDAS (for microphthalmia, dermal aplasia, and sclerocornea), and argued that (in contrast to focal dermal hypoplasia) the erythematous lesions of dermal aplasia do not show herniation of fatty tissue. Subsequent histologic examination of skin biopsies of the linear, reticulated skin defects in six reported individuals yielded varied results, all confirming that dermal aplasia is not a histologic feature of MLS syndrome. Bird et al [1994] described focal areas of deficient collagen relative to the surrounding tissue, but absence of dermal aplasia. Eng et al [1994] described a necrotic epidermis with an intact basement membrane and no signs of inflammation. Paulger et al [1997] described smooth muscle hamartoma with overlying acanthotic epidermis, a thickened corneal layer, focal parakeratosis, foci of superficial erosion, and erector pili muscles in unusually large numbers in the surrounding dermis. Stratton et al [1998] described smooth muscle hamartoma rather than dermal aplasia. Zvulunov et al [1998] described a mild perivascular lymphocytic infiltrate in the upper dermis and regeneration of the epidermis. Electron microscopy revealed peculiar cytoplasmic bodies within keratinocytes. Enright et al [2003] described irregular bundles of smooth muscle in the deep dermis resembling hypertrophied arrectores pilaris muscles, a basket-weave orthokeratosis, a granular layer of varying thickness vacuolar alteration of the basal layer, and an interface infiltrate of lymphocytes extending into the epidermis.Eye findings. With microphthalmia and/or anophthalmia, developmental abnormalities are evident at birth in 92% of affected individuals (Figure 2) (see Anophthalmia/Microphthalmia Overview). Both microphthalmia and anophthalmia can be unilateral or bilateral. Other ocular abnormalities are described in Diagnosis.

Differential DiagnosisGoltz syndrome, also known as focal dermal hypoplasia, is characterized by distinctive skin findings (dermal hypoplasia) and ophthalmologic manifestations similar to those observed in microphthalmia with linear skin defects (MLS) syndrome. However, limb and skeletal malformations that are common in Goltz syndrome are rarely seen in MLS syndrome. Goltz syndrome is caused by deletions and point mutations of PORCN; thus, MLS syndrome and focal dermal hypoplasia are not allelic, as had been previously proposed. Inheritance is X-linked with male lethality. Incontinentia pigmenti (IP) affects the skin, hair, teeth, nails, eyes, and central nervous system. Characteristic skin lesions evolve through four stages: (I) blistering (birth to age ~4 months); (II) a wart-like rash (for several months); (III) swirling macular hyperpigmentation (age ~6 months into adulthood); (IV) linear hypopigmentation. Alopecia, hypodontia, abnormal tooth shape, and dystrophic nails are observed. Ocular abnormalities are reported in 35% of individuals with IP and include neovascularization of the retina, pigment epithelial mottling, microphthalmia, and anophthalmia. Neurologic findings including cognitive delays/intellectual disability are occasionally seen. NEMO is the only gene known to be associated with IP. Inheritance is X-linked with male lethality. Oculocerebrocutaneous syndrome (OCCS), characterized by orbital cysts and anophthalmia or microphthalmia, focal skin defects, brain malformations that include polymicrogyria, periventricular nodular heterotopias, enlarged lateral ventricles, and agenesis of the corpus callosum, is predominant in males and has a pathognomonic mid-hindbrain malformation [Moog et al 2005] (see also Polymicrogyria Overview).Aicardi syndrome was initially described as a triad of agenesis of the corpus callosum, typical chorioretinal lacunae, and infantile spasms; however, with the ascertainment of more cases, it has become clear that other neurologic heterotopias, polymicrogyria, and systemic defects including costovertebral anomalies are common. Moderate- to-severe global developmental delay and intellectual disability are expected. Medically refractory epilepsy with a variety of seizure types develops over time. Other features include characteristic facial features, microphthalmia, and pigmentary lesions of the skin. To date, the gene in which mutation is causative has not been mapped and is not known; however, mutations in HCCS have not been found in Aicardi syndrome. Hence, MLS and Aicardi syndrome are likely not allelic. Inheritance is presumed X-linked dominant, male-lethal because only females or males with 47,XXY karyotype are known.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).

ManagementEvaluations Following Initial DiagnosisTo establish the extent of disease in an individual diagnosed with microphthalmia with linear skin lesions (MLS) syndrome, the following evaluations are recommended:Ophthalmologic examinationDermatologic evaluation to look for skin lesionsBrain MRI with and without contrast to evaluate for corpus callosum dysgenesis and other neurologic abnormalitiesDevelopmental assessment, with further evaluation if significant delays are identifiedHearing evaluationCardiac examinationConsideration of abdominal MRI and standard protocols for management of diaphragmatic herniaGenetics consultationTreatment of ManifestationsThe following are appropriate:Use of a prosthesis in severe microphthalmia and anophthalmia. In some cases ophthalmologic surgery can be considered to expand the palpebral fissures and orbit by fitting the infant with prostheses of progressively increasing size.Considerations for surgical intervention in severe microphthalmia and anophthalmia are best made after age six months, when postnatal growth of the orbit can be assessed.Regular care of a dermatologist for individuals with significant skin lesions Referral to a pediatric neurologist for evaluation and treatment if microcephaly, seizures, and/or other neurologic abnormalities are presentAppropriate developmental stimulation and special education as indicated for developmental delayRoutine care for diaphragmatic hernia, cardiomyopathy, congenital heart defects, and other malformations, when presentSurveillance Monitoring and follow-up with ophthalmologist, dermatologist, pediatric neurologist, or other professionals as needed is appropriate. For those with cardiomyopathy, complete and periodic cardiac evaluation by a cardiologist experienced in the diagnosis and treatment of heart failure is needed.Evaluation of Relatives at RiskSee Genetic Counseling for issues related to testing of at-risk relatives for genetic counseling purposes.Therapies Under InvestigationSearch ClinicalTrials.gov for access to information on clinical studies for a wide range of diseases and conditions. Note: There may not be clinical trials for this disorder.

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. Microphthalmia with Linear Skin Defects Syndrome: Genes and DatabasesView in own windowGene SymbolChromosomal LocusProtein NameLocus SpecificHGMDHCCSXp22​.2Cytochrome c-type heme lyaseHCCS @ LOVDHCCSData 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 Microphthalmia with Linear Skin Defects Syndrome (View All in OMIM) View in own window 300056HOLOCYTOCHROME C SYNTHASE; HCCS 309801MICROPHTHALMIA, SYNDROMIC 7; MCOPS7Normal allelic variants. HCCS has seven exons, six of which are coding exons. The gene spans 11.8 kb, and its transcribed mRNA is long at 2365 bp. It is not known to undergo alternative splicing (see Table 2).Pathologic allelic variants. Disease-causing mutations include a nonsense mutation, c.589C>T (exon 6, p.Arg197X); two missense mutations, c.649C>T (exon 7, p.Arg217Cys) and c.475G>A (exon 5, p.Glu159Lys); as well as an HCCS deletion of exons 1-3 [Wimplinger et al 2006, Wimplinger et al 2007b] (see Table 2).Table 2. Selected HCCS Allelic Variants View in own windowClass of Variant AlleleDNA Nucleotide ChangeProtein Amino Acid ChangeReference SequencesNormalrs2070163 p.Ala72ValNM_005333​.4
NP_005324​.3rs34228583p.= ^{1Pathologicc.589C>Tp.Arg197Xc.649C>Tp.Arg217Cysc.475G>Ap.Glu159LysSee Quick Reference for an explanation of nomenclature. GeneReviews follows the standard naming conventions of the Human Genome Variation Society (www​.hgvs.org).1. p.= designates that protein has not been analyzed, but no change is expected. Normal gene product. HCCS is expressed in a wide variety of tissues and encodes a mitochondrial enzyme of 268 amino acids, the holocytochrome c-type synthase, which catalyzes the covalent attachment of heme to apocytochrome c, thereby leading to the mature form holocytochrome c [Bernard et al 2003]. The product of the HCCS-catalyzed reaction, cytochrome c, has two cellular functions: it is implicated in oxidative phosphorylation (OXPHOS), and it is released from mitochondria upon proapoptotic stimuli, thus playing an important role in caspase-dependent apoptosis [Jiang & Wang 2004].Abnormal gene product. Microphthalmia with linear skin defects (MLS) syndrome is caused by loss-of-function mutations in HCCS and cytogenetically visible deletions or microdeletions covering (part of) HCCS. It is currently unknown how the mutations in HCCS could cause a peculiar pathologic phenotype like MLS syndrome. Recently it was hypothesized that deficiency of HCCS may not only cause functional deficits in OXPHOS, but may also lead to severe constraints in the process of apoptosis. Thus, functional nullisomy of HCCS may disturb the balance between necrosis and apoptosis and push cell death toward necrosis [Wimplinger et al 2006]. Necrosis bears the danger of inflammatory reactions, leading to substantial damage of neighboring cells that could be a key element in developing eye malformations as well as other MLS syndrome-specific features in affected individuals.}