DiagnosisClinical DiagnosisMales with Lowe syndrome. Varying degrees of severity of the following developmental defects have been noted among affected individuals [Lowe et al 1952, Gropman et al 2000, Nussbaum & Suchy 2001]. The disorder is suspected clinically in males who have a combination of the following features: Bilateral dense congenital cataracts Infantile congenital hypotonia Delayed development Proximal renal tubular transport dysfunction of the Fanconi type characterized by varying degrees of bicarbonaturia and acidosis, phosphaturia, aminoaciduria, and low molecular-weight (LMW) proteinuria (including retinol binding protein, N-acetyl glucosaminidase, and albumin); except for LMW proteinuria, the Fanconi syndrome features do not appear until after the first few months of life. Other frequently noted findings:Infantile glaucoma (in ~50% of males) Seizures Absent deep tendon reflexes Maladaptive behaviors, especially stubbornness, tantrums, stranger anxiety, and stereotypy (complex repetitive behaviors) Short stature Mild ventriculomegaly and multiple, periventricular, variably sized, small cysts on MRI in approximately one third of affected individuals [Charnas & Gahl 1991, Demmer et al 1992, Carroll et al 1993] Hypercalciuria with nephrocalcinosis and nephrolithiasis Pathologic fractures and bone demineralization in the presence of normal serum concentrations of calcium, phosphorus, and vitamin D metabolites Dental cysts and dysplastic dentin formation of the teeth Skin cysts similar to eruptive vellus hair cysts Prolonged or delayed bleeding following surgery, such as cataract extraction [Lasne et al 2010].Female carriers of Lowe syndrome. Approximately 95% of postpubertal carrier females have characteristic findings in the lens of each eye when the lens is evaluated through a dilated pupil with a slit lamp by an experienced ophthalmologist. The lens findings have correlated with the results of molecular genetic studies in predicting carrier status of postpubertal females [Lin et al 1999, McSpadden 2000, Roschinger et al 2000, Nussbaum & Suchy 2001]. While the lens findings may be present in prepubertal females as well (especially the less common axial posterior central opacity), their absence does not exclude carrier status. Most carrier females show numerous irregular, punctate, smooth, off-white (white to gray) opacities, present in the lens cortex, more in the anterior cortex than the posterior cortex and wrapping around the lens equator. Classically, the nucleus is spared. On retroillumination, the opacities are distributed in a radial, spoke-like pattern and can be relatively dense in a wedge shape comparable to an hour or two on the face of a clock, alternating with a similar-sized wedge with few to no opacities.A few carriers (~10%) have a dense central precapsular dead-white cataract at the posterior pole of the lens that may be visually significant if it is large. TestingLow molecular-weight (LMW) proteinuria. LMW proteinuria, characterized by the excretion of proteins such as retinal binding protein and N-acetyl glucosaminidase, is seen in Lowe syndrome, the allelic disorder Dent disease (see Allelic Disorders), and many other diseases associated with the Fanconi syndrome. In Lowe syndrome, LMW proteinuria can be seen early in life even in the absence of clinically significant aminoaciduria or other renal tubular abnormalities [Laube et al 2004]. Thus, LMW may be the most sensitive marker of the renal dysfunction that occurs in this disorder. Inositol polyphosphate 5-phosphatase OCRL-1 activityMales. Activity of the enzyme inositol polyphosphate 5-phosphatase OCRL-1 (phosphatidylinositol polyphosphate 5-phosphatase OCRL-1) can be measured in cultured skin fibroblasts to confirm the diagnosis in affected males [Suchy et al 1995, Zhang et al 1995]. Affected males have less than 10% normal activity of the enzyme. Such testing is abnormal in more than 99% of affected males.
Note: Peripheral blood samples cannot be used because the enzyme is not present in lymphocytes [Nussbaum & Suchy 2001]. Carrier females. Measurement of activity of the enzyme inositol polyphosphate 5-phosphatase OCRL-1 is not accurate for carrier detection because of lyonization (random X-chromosome inactivation), which results in a wide range of "normal" activity in females [Lin et al 1999]. Karyotype. Translocations between an autosome and an X chromosome with a breakpoint through the OCRL locus (Xq26.1) have been observed [Hodgson et al 1986, Mueller et al 1991]. Other. No specific findings are noted on muscle biopsy, nerve conduction testing, or electromyography [McSpadden 2000, Nussbaum & Suchy 2001]. Molecular Genetic Testing Gene. OCRL is the only gene in which mutation is known to cause Lowe syndrome. Clinical testing Table 1. Summary of Molecular Genetic Testing Used in Lowe SyndromeView in own windowGene SymbolTest MethodMutations DetectedMutation Detection Frequency by Test Method ^{1Test AvailabilityMalesHeterozygous FemalesOCRLSequence analysisSequence variants 295% 3, 495% 5ClinicalDeletion / duplication analysis 6Deletion / duplication of one or more exons or the whole geneUnknownLinkage analysis 7Not applicable Not applicable 1. The ability of the test method used to detect a mutation that is present in the indicated gene2. Examples of mutations detected by sequence analysis may include small intragenic deletions/insertions and missense, nonsense, and splice site mutations; typically, exonic or whole-gene deletions/duplications are not detected. There are no common mutations. Although a few mutations have been noted in more than one affected individual, most mutations are unique to a family.3. 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. 4. Includes the mutation detection frequency using deletion/duplication analysis.5. Sequence analysis of genomic DNA cannot detect deletion of one or more exons or the entire X-linked gene in a heterozygous female.6. Testing that identifies deletions/duplications not readily detectable by sequence analysis of the coding and flanking intronic regions of genomic DNA; included in the variety of methods that may be used are: quantitative PCR, long-range PCR, multiplex ligation-dependent probe amplification (MLPA), and chromosomal microarray (CMA) that includes this gene/chromosome segment.7. Linkage analysis is can be used when an exact DNA mutation or deletion cannot be identified in the family [Reilly et al 1988, Wadelius et al 1989, Lin et al 1999]. Linkage studies are based on accurate diagnosis of Lowe syndrome in the affected family members (e.g., with enzyme assay confirmation), understanding of the genetic relationships in the family, and the availability and willingness of family members to be tested. The markers used for Lowe syndrome linkage are highly informative and tightly linked to the OCRL locus [Nussbaum et al 1997]. In informative families, linkage analysis and a dilated slit-lamp eye examination may be used to establish a female's carrier status with approximately 94% accuracy. Interpretation of test results. For issues to consider in interpretation of sequence analysis results, click here.Information on specific allelic variants may be available in Molecular Genetics (see Table A. Genes and Databases and/or Pathologic allelic variants).Testing StrategyTo confirm/establish the diagnosis in a male probandTesting of inositol polyphosphate 5-phosphatase OCRL-1 activity in cultured skin fibroblasts is the diagnostic test of choice. Sequence analysis of OCRL can be used for confirmation of diagnosis; it is necessary for identification of the disease-causing mutation in a family for purposes of carrier testing and prenatal diagnosis. Consider deletion/duplication analysis if sequence analysis of some or all exons fails to generate any sequence information (suggesting a partial or whole-gene deletion in a hemizygous male). Linkage analysis may be considered for families in whom an exact DNA mutation or deletion cannot be identified [Reilly et al 1988, Wadelius et al 1989, Lin et al 1999] (Table 1, footnote 7). Note that linkage analysis may be considered in families with only one affected male; however, the possibility of a new mutation in the affected family member makes interpretation challenging. Germline mosaicism, which can confound studies that rely on linkage alone for carrier detection, has also been documented in Lowe syndrome [Satre et al 1999, Monnier et al 2000].To confirm/establish the diagnosis in a female proband. All females suspected of having the Lowe syndrome should have detailed cytogenetic studies in addition to enzymatic and molecular testing for the disorder because of the possibility of an X;autosome translocation. Carrier testing for at-risk relatives requires prior identification of the disease-causing mutation in the family.Note: (1) Carriers are heterozygotes for this X-linked disorder and commonly develop lens changes characteristic of the disorder by the latter half of the first decade. (2) Identification of female carriers requires either (a) prior identification of the disease-causing mutation in the family or, (b) if an affected male is not available for testing, molecular genetic testing first by sequence analysis, and then, if no mutation is identified, by methods to detect gross structural abnormalities.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) DisordersMutations in OCRL have been found in approximately 25% of 80 families with Dent disease who did not demonstrate mutations in CLCN5. Mutations in OCRL can therefore occur within individuals with the isolated renal phenotype of Dent disease who lack the cataracts, renal tubular acidosis, and neurologic abnormalities that are characteristic of Lowe syndrome; these individuals are classified as having Dent-2 disease [Hoopes et al 2005, Bökenkamp et al 2009]. Occasionally, individuals with Dent-2 disease and OCRL mutations manifest mild developmental delay and visually insignificant peripheral cataracts. Whether these extrarenal manifestations are chance occurrences or indicate overlap between Dent-2 and Lowe syndrome, both caused by OCRL mutations, remains to be elucidated.}

Natural HistoryThe major clinical manifestations found in males with Lowe syndrome involve the eyes, central nervous system, and kidneys. As molecular genetic testing and biochemical studies of OCRL have become more widespread, phenotypic heterogeneity appears to be substantially greater than previously suspected, such that individuals who lack certain features of Lowe syndrome can still have mutations in OCRL. Usually only males have the disorder. A few affected females with the clinical manifestations of Lowe syndrome have been reported (see Testing, Karyotype).Eyes. Dense congenital cataracts, formed as a result of abnormal metabolism or migration of the embryonic lens epithelium, are found in all affected boys. Microphthalmos and enophthalmos, related to the lens abnormality, are noted occasionally. Although present at birth, the cataracts may not be detected until a few weeks of life. Infantile glaucoma, present in approximately 50% of affected males, is difficult to control and often results in buphthalmos (enlarged eyes) and progressive visual loss [McSpadden 2000, Nussbaum & Suchy 2001]. The glaucoma is severe and requires surgical management. Strabismus, retinal dystrophy, secondary corneal scarring, and calcific band keratopathy with keloid formation [Cibis et al 1982] may cause additional visual impairment [McSpadden 2000, Nussbaum & Suchy 2001]. All boys have impaired vision; corrected acuity is rarely better than 20/100 [McSpadden 2000, Nussbaum & Suchy 2001]. With decreased visual acuity, nystagmus develops early in life, even with early and uncomplicated surgery. Self-stimulatory activity also increases, i.e., rhythmic flapping of the hands, eye rubbing, and repetitive rocking movements. Despite aggressive intervention, visual disability may progress to blindness. Central nervous system. Generalized infantile hypotonia is noted soon after birth and is of central origin. Deep tendon reflexes are usually absent. Hypotonia may slowly improve with age, but neither normal motor tone nor strength is ever achieved. Feeding difficulties in infancy associated with poor head control, sucking, or swallowing may be a consequence of the hypotonia. Decreased motor tone also results in delayed motor milestones. Independent ambulation occurs in approximately 25% of boys between age three and six years and in 75% by age six to 13 years. Some never walk and require the use of a wheelchair for mobility [McSpadden 2000]. Approximately 50% of affected boys have seizure disorders, most often of the generalized type and usually starting before age six years [McSpadden 2000].Behavior problems (i.e., self-stimulation or stereotypic and obsessive-compulsive behaviors) are frequent and include many problems common to visually and intellectually handicapped individuals. Occasionally, violent tantrums or aggressive and self-abusive behaviors occur [Charnas & Gahl 1991, Kenworthy et al 1993].Almost all affected males have some degree of intellectual impairment. Between 10% and 25% of affected males function in the low-normal or borderline range and approximately 25% function in the mild-to-moderate range of intellectual disability. The remainder functions in the severe-to-profound range of intellectual handicap [Kenworthy et al 1993]. Delayed language development is evident in early childhood. Most individuals learn to communicate verbally to some extent by age seven years; some eventually become quite talkative [McSpadden 2000]. Love of music and rhythm are notable. As adults, most affected men reside with their families. A few are functional enough to live in a group home or even independently with appropriate assistance and guidance.Kidneys. Affected boys have varying degrees of proximal renal tubular dysfunction of the renal Fanconi type. The features of symptomatic Fanconi syndrome do not usually become manifest until after the first few months of life, except for low molecular-weight (LMW) proteinuria (see Testing). LMW proteins are normally filtered by the glomerulus, then reabsorbed in the proximal tubule through endocytosis and metabolized in lysosomes in proximal tubular cells. When reabsorption and/or metabolism are dysfunctional, LMW proteins, including retinol binding protein, beta-2-microglobulin and the lysosmal enzyme N-acetyl glucosaminidase, are lost in the urine. LMW proteinuria has been identified as early as just after birth [Laube et al 2004] and may be the most sensitive marker for renal involvement of Lowe syndrome. The molecular size of albumin is at the upper end of the size range for LMW proteins, so the small percentage of albumin that is normally filtered by the glomerulus is also reabsorbed and metabolized by the proximal tubule via the LMW protein transport process. In Lowe syndrome, proximal renal tubular dysfunction often leads to clinically apparent albuminuria (urine dipstick albumin 1-4+), while serum albumin remains normal. Albuminuria is better known as a marker of glomerular injury in other diseases such as diabetes mellitus; in Lowe syndrome it likely reflects proximal tubular dysfunction, especially early in life before chronic renal failure occurs.The spectrum of proximal renal tubular transport dysfunction varies widely in Lowe syndrome, but has not been associated with specific OCRL mutations. All boys have LMW proteinuria and albuminuria, likely from disordered metabolism in the proximal tubular cell downstream from endocytosis and postendocytic membrane trafficking [Cui et al 2010]. Some boys develop full-blown renal Fanconi syndrome with bicarbonaturia and renal tubular acidosis, phosphaturia with hypophosphatemia and renal rickets, aminoaciduria, LMW proteinuria, sodium and potassium wasting, and polyuria with an apparent urine concentrating defect from the massive solute loss in the urine. Few of these boys have renal glucose wasting, which is frequently observed in other diseases with full-spectrum renal Fanconi syndrome [Bockenhauer et al 2008]. Other boys have little or no bicarbonaturia and phosphaturia, but LMW proteinuria and hypercalciuria with nephrocalcinosis and nephrolithiasis similar to Dent disease [Sliman et al 1995, Hoopes et al 2005, Bockenhauer et al 2008].Progressive glomerulosclerosis likely results from progressive renal tubular injury, which eventually may lead to chronic renal failure and end-stage renal disease (ESRD) between the second and fourth decades of life [McSpadden 2000, Nussbaum & Suchy 2001].Most males do not live past age 40 years. In older individuals, death has been related to progressive renal failure or scoliosis. Death from dehydration, pneumonia, and infections occurs at all ages [McSpadden 2000].Other clinical manifestations. Although birth length is usually normal, linear growth velocity is below normal and short stature becomes evident by age one year. The average adult height is approximately 155 cm [McSpadden 2000]. Chronic renal disease and acidosis along with renal rickets or other bone disease may contribute to the short stature. Bone disease in affected boys may be related to Fanconi syndrome with phosphaturia, inadequate renal production of 1,25-dihydroxyvitamin D, and chronic acidosis, and appear as classic changes of rickets on bone radiographs. However, even in the presence of well-corrected Fanconi syndrome and no findings of rickets, some boys have repeat pathologic bone fractures with poor healing and bone demineralization on radiographs or bone densitometry [E Brewer, personal observation]. Whether some of the bone disease is related to inactivity resulting from muscle hypotonia and immobilization in severely affected boys or to a primary defect in bone mineralization/molecular transport requires further study. Undescended testes (cryptorchidism) are noted in approximately one third of affected boys [McSpadden 2000].Failure to thrive may occur because of insufficient caloric intake.Gastroesophageal reflux, most common in infancy, may be seen at any age.Aspiration of food along with a decreased ability to cough effectively to clear lung fields may lead to atelectasis, pneumonia, or chronic lung disease.Poor abdominal muscle tone increases the risk for chronic constipation and the development of (predominantly inguinal) hernias.Decreased truncal motor tone increases the risk of developing scoliosis, present in approximately 50% of affected boys [McSpadden 2000].Hypermobile joints may result in joint dislocation, especially of the hips and knees.Puberty may be delayed in onset; otherwise, male secondary sexual development is normal. In affected teenagers and adults, joint swelling, arthritis, tenosynovitis, and subcutaneous benign fibromas, often on the hands and feet and most especially in areas of repeated trauma, are noted frequently [Athreya et al 1983, Elliman & Woodley 1983].Dental malformations with decreased dentin formation may also be related to a primary dental abnormality in Lowe syndrome.Superficial cysts may occur in the mouth and on the skin. In one report of an individual with a clinical diagnosis of Lowe syndrome who had not had definitive laboratory diagnosis by enzyme assay or molecular genetic testing, biopsy of the cysts showed the histologic findings of an eruptive vellus hair cyst [Nandedkar et al 2004]. Those on the lower back and buttocks can become painful and occasionally infected. Cysts have also been found in imaging studies of the kidneys and brain. These findings suggest that an abnormality in connective tissue may also be involved in the pathogenesis of the disorder [McSpadden 2000, Nussbaum & Suchy 2001]. Elevated serum concentration of high-density cholesterol, creatinine kinase, AST, and LDH are occasionally noted and are of uncertain significance [McSpadden 2000, Nussbaum & Suchy 2001]. Decreased plasma carnitine concentration has been reported in approximately one third of individuals with Lowe syndrome and may normalize with oral carnitine therapy [Gahl et al 1988]. Whether carnitine wasting in the urine from severe Fanconi syndrome is the etiology of carnitine deficiency has not been studied adequately in Lowe syndrome. An increased incidence of postoperative bleeding has been reported in a study of medical records of six males with Lowe syndrome followed in a pediatric nephrology unit. To investigate this finding, coagulation profiles (INR and PTT), platelet counts, and von Willebrand factor structure and levels were examined; they were normal in all six. However, there appeared to be an intrinsic platelet defect in these individuals that can be detected using a platelet function analyzer (PFA-100) [Lasne et al 2010].

Genotype-Phenotype CorrelationsTo date, correlation of genotype with phenotype has not been established. Differing clinical courses have been noted in unrelated individuals with the same OCRL mutation [Leahey et al 1993]. It is also now apparent that highly deleterious mutations in OCRL that result in total loss of OCRL expression occur both in individuals with Lowe syndrome and in individuals with Dent disease, but intrafamilial variability has not been documented.

Differential DiagnosisLow molecular-weight (LMW) proteinuria is a feature of Fanconi syndrome and can also be seen in other conditions including cystinosis, nephrotoxic drug injury to the tubules (e.g., aminoglycosides), and acute tubulointerstitial renal transplant rejection with tubular injury. However, the LMW proteinuria appears to be a more prominent feature of renal tubular dysfunction in Lowe syndrome and Dent disease than in these other disorders.Disorders with congenital or neonatal-onset cataracts, hypotonia, proximal renal tubular dysfunction, and delayed development may be considered in the differential diagnosis. These include the following:Generalized congenital infections (e.g., rubella) Peroxisomal biogenesis disorders, Zellweger syndrome spectrum. Affected children are hypotonic, feed poorly, and have distinctive facies. Neonatal seizures are common. Bony stippling (chondrodysplasia punctata) of the patella(e) and other long bones may occur. Older children have retinal dystrophy, sensorineural hearing loss, developmental delay with hypotonia, and liver dysfunction. Measurement of plasma very-long-chain fatty acid (VLCFA) levels is the most commonly used and most informative initial screen. Elevation of C26:0 and C26:1 and the ratios C24/C22 and C26/C22 is consistent with a defect in peroxisomal fatty acid metabolism. Mutations in 12 different PEX genes (which encode peroxins, the proteins required for normal peroxisome assembly) have been identified. Nance-Horan syndrome (OMIM 302350) is an X-linked syndrome of dense cataracts and microcornea associated with dental anomalies including cone-shaped incisors, supernumerary teeth, and facial dysmorphisms such as anteverted pinnae. Female carriers have Y-shaped sutural cataracts and may have dental anomalies as well. Renal abnormalities are not seen, nor is the facial appearance of sunken orbits and bitemporal hollowing seen frequently in Lowe syndrome. Mutations at a novel X-linked gene, NHS, at Xp22, are responsible for the Nance-Horan syndrome. Smith-Lemli-Opitz syndrome is a congenital multiple anomaly syndrome caused by an abnormality in cholesterol metabolism resulting from deficiency of the enzyme 7-dehydrocholesterol reductase. It is characterized by prenatal and postnatal growth retardation, microcephaly, moderate to severe intellectual disability, and multiple major and minor malformations. The malformations include distinctive facial features, cleft palate, cardiac defects, underdeveloped external genitalia in males, postaxial polydactyly, and 2-3 syndactyly of the toes. The clinical spectrum is wide and individuals have been described with normal development and only minor malformations. The diagnosis relies on elevated serum concentration of 7-dehydrocholesterol (7-DHC) or an elevated 7-dehydrocholesterol:cholesterol ratio. Molecular genetic testing for mutations of DHCR7 (the gene in which mutation is causative) is used primarily for carrier detection and prenatal diagnosis. Congenital myotonic dystrophy type 1 (DM1) is characterized by hypotonia and severe generalized weakness at birth, often with respiratory insufficiency and early death; intellectual disability is common. DM1 is caused by expansion of a CTG trinucleotide repeat in DMPK. The diagnosis is suspected in individuals with characteristic muscle weakness and is confirmed by molecular genetic testing of DMPK. Although CTG repeat length exceeding 35 repeats is abnormal, the development of congenital myotonic dystrophy requires repeat lengths greater than 2000. Disorders of mitochondrial oxidative phosphorylation (see Mitochondrial Disorders Overview). Common clinical features of mitochondrial disease include ptosis, external ophthalmoplegia, proximal myopathy and exercise intolerance, cardiomyopathy, sensorineural deafness, optic atrophy, pigmentary retinopathy, and diabetes mellitus. The central nervous system findings are often fluctuating encephalopathy, seizures, dementia, migraine, stroke-like episodes, ataxia, and spasticity. Mitochondrial diseases are a clinically heterogeneous group of disorders that arise as a result of dysfunction of the mitochondrial respiratory chain. They can be caused by mutations of nuclear or mitochondrial DNA (mtDNA). In some individuals, the clinical picture is characteristic of a specific mitochondrial disorder, and the diagnosis can be confirmed by molecular genetic testing of DNA extracted from a blood sample. In many individuals, however, a more structured approach is required for diagnosis, including family history, blood and/or CSF lactate concentration, neuroimaging, cardiac evaluation, and muscle biopsy for histologic or histochemical evidence of mitochondrial disease, and molecular genetic testing for an mtDNA mutation. Cystinosis is characterized by poor growth, renal tubular Fanconi syndrome, renal glomerular failure, and involvement of other tissues and organ systems. In untreated individuals, failure to grow is generally noticed at age six to nine months. Cystine-depleting therapy begun just after birth can attenuate the Fanconi syndrome. In untreated individuals, glomerular function gradually deteriorates, resulting in renal failure at approximately age ten years. A slit-lamp examination of the cornea showing typical cystine crystals is diagnostic for cystinosis. This should be confirmed by measurement of leucocyte cystine, which is best performed using the cystine binding protein assay. Mutations in CTNS cause cystinosis. Dent disease 2 has the phenotype of Dent disease 1 with LMW proteinuria, aminoaciduria, and hypercalciuria with nephrocalcinosis and nephrolithiasis, but no mutation in CLCN5 [Hoopes et al 2005]. Some affected boys have mutations in OCRL, but do not have the typical facies, behavioral stereotypy, renal tubular acidosis, and cataracts of Lowe syndrome and only rarely have mild intellectual disability. 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 Lowe syndrome, the following evaluations are recommended:Infants should be evaluated for feeding problems and gastroesophageal reflux, including a pH probe study. Growth parameters should be measured and plotted on a growth chart. An ophthalmologic evaluation is needed to assess for cataract and glaucoma. Behavior problems may necessitate the use of anesthesia for eye examinations. Renal tubular function should be assessed by measurement of serum electrolytes, calcium, phosphorus and creatinine, and simultaneous urinalysis and random urine pH, electrolytes, calcium, phosphorus, creatinine, amino acids, protein and retinol binding protein, and/or N-acetyl glucosaminidase, if available. Interpretation of these results allows diagnosis of type 2 renal tubular acidosis, hypokalemia, phosphate wasting with decreased tubular reabsorption of phosphate (TRP), hypercalciuria (urine calcium/creatinine ratio >0.02), amino aciduria, albuminuria (urine dipstick positive albumin and urine protein/creatinine ratio >0.2), low molecular-weight proteinuria, and renal glomerular insufficiency (serum creatinine). If acidosis or phosphaturia is present, serum concentration of 1,25-dihydroxyvitamin D and parathyroid hormone should be measured and bone radiographs should be obtained to evaluate for renal rickets. Bone radiographs should also be obtained in boys with bone pain or point tenderness to evaluate for fractures in the absence of rickets.If hematuria or hypercalciuria is present, a renal ultrasound examination should be performed to screen for nephrocalcinosis and nephrolithiasis. Plasma carnitinine may be measured to evaluate for carnintine deficiency. Developmental and behavioral evaluations should be completed. An electroencephalogram (EEG) is often needed to document the exact type of seizures and to determine appropriate anticonvulsant therapy. Treatment of ManifestationsManagement of the varying clinical problems usually requires more than one medical specialist; experts in pediatric ophthalmology, nephrology, clinical biochemical genetics, metabolism, nutrition, endocrinology, neurology, child development, behavior, rehabilitation, general surgery, orthopedics, or dentistry may be involved.Eyes. Treatment of the eye problems usually requires an experienced (preferably pediatric) ophthalmologist; cataract surgeons and glaucoma specialists may also be needed. Early removal of cataracts is recommended to promote proper visual stimulation and development. Postoperatively, eyeglasses or contact lenses help to improve vision. Surgical implantation of artificial lenses is not recommended because of the high prevalence of infantile glaucoma.Despite management with medical and surgical measures, glaucoma is often difficult to control.Special services for the visually handicapped should be included in any rehabilitation plan.Central nervous system. In infancy, feeding and nutrition problems related to hypotonia may be substantial. Occasionally, nasogastric tube feedings or feeding gastrostomy, with or without fundoplication, may be necessary to achieve appropriate nutrition. Occupational or speech therapists who specialize in feeding problems may be of assistance. Gastroesophageal reflux usually responds to standard anti-reflux measures such as thickened feedings and elevation of the head of the bed. Some individuals need medications to control gastric acidity and to promote gastric emptying; others require surgery. Most seizure disorders can be controlled with anticonvulsant therapy. Programs to promote optimal psychomotor development should be started in early infancy. Early childhood and preschool intervention programs, e.g., First Steps or Head Start, and later public or private school programs should evaluate the abilities and specific needs of the child and formulate an individualized educational plan (IEP). Physical therapy, occupational therapy, speech and language therapy, special education services, and services for the visually impaired are usually included in the plan. A behavior modification plan along with antidepressant and/or antipsychotic medications may be needed for behavior control. Kidney. Those individuals with renal Fanconi syndrome and type 2 renal acidosis should be treated with oral supplements of sodium and potassium bicarbonate or citrate to correct acidosis and hypokalemia. Doses need to be titrated to individual needs based on "trough" blood concentrations of serum electrolytes (sodium, potassium, chloride, and total carbon dioxide). (Trough levels are blood concentrations measured just before a scheduled dose.) Treatment with oral phosphate, along with oral calcitriol (1,25-dihydroxyvitamin D₃), is needed to correct hypophosphatemia and renal rickets of the Fanconi syndrome. Doses should also be titrated to individual needs based on trough blood concentration for phosphorus and serum concentrations of 1,25-dihydroxyvitamin D, calcium, and intact parathyroid hormone.An increased requirement for fluids, along with the electrolyte and bicarbonate requirements, places affected individuals at high risk for metabolic imbalance during illness (especially those associated with vomiting or diarrhea) or when fasting, e.g., with surgical procedures. At such times, intravenous replacement of fluids, bicarbonate, and electrolytes is important and may need to be done in anticipation of problems to prevent severe electrolyte disturbances and dehydration. Progressive glomerulosclerosis likely results from progressive renal tubular injury, which eventually may lead to chronic renal failure and end-stage renal disease (ESRD) between the second and fourth decades of life [McSpadden 2000, Nussbaum & Suchy 2001]. Treatment of ESRD with chronic dialysis and renal transplant may be successful in selected patients [Tricot et al 2003]. Although experience is limited, at least seven adult men with Lowe syndrome and ESRD have been treated successfully over a few years, including three with chronic hemodialysis, one with chronic home peritoneal dialysis, and three with renal transplants [E Brewer, personal observation].Other. Human growth hormone therapy has been used successfully to improve growth velocity in some boys [McSpadden 2000]. The potential benefits of such therapy must be weighed against its costs/limitations. Most undescended testes descend with time into the scrotum; some require hormone therapy and/or surgical correction. In older individuals, bracing or surgery may be needed to arrest or correct severe or progressive scoliosis and joint hypermobility. Resection of fibromas and cutaneous cysts may be needed if they are painful, have recurrent infections, or limit function. SurveillanceEye evaluations should be done at regular intervals, depending on the type and severity of abnormality. No formal guidelines exist. Because approximately 50% of males either present with glaucoma or develop glaucoma in time, regardless of cataract surgery, intraocular pressure should be monitored at least every six months life-long. Presence of clinical findings suggestive of increased intraocular pressure (e.g., excessive tearing, eye rubbing, change in the clarity/transparency of the cornea) warrant prompt evaluation. Kidney function should be assessed at least yearly with measurement of serum concentrations of electrolyte, blood urea nitrogen (BUN), creatinine, calcium, phosphorus, albumin, intact parathyroid hormone, and 1,25-dihydroxyvitamin D. If the patient has Fanconi syndrome requiring therapy with supplemental bicarbonate or citrate, serum concentrations of phosphate or calcitriol should be measured every three to six months or more often after dose changes. BUN and serum creatinine are appropriate screening tests to detect the onset of chronic renal failure and to monitor its progression. Urinalysis and random urine protein, calcium, and creatinine are useful to follow proteinuria and hypercalciuria.If the patient has renal Fanconi syndrome and bone disease, radiographs of the long bones and growth plates should be obtained at regular intervals as needed, but no more than every six months.Growth should be monitored regularly with height/length and weight plotted on growth charts for age. Height/length and weight should be measured more frequently in infants (every 2-3 months) than in older children and adolescents who are still growing (every 3-6 months). If patients are treated with growth hormone, growth assessment every three months is indicated. Developmental progress should be assessed and the educational plan updated twice yearly for the first three years and annually after that. Any regression in abilities should be investigated with high-resolution imaging studies of the central nervous system. Scoliosis and joint problems should be monitored as part of a routine annual physical examination. Dental examinations should be performed twice a year by a pediatric dentist experienced in treating children with developmental delay. Agents/Circumstances to AvoidCorneal contact lenses. Because of the associated risks of corneal keloid formation and the inherent difficulties that the person with Lowe syndrome has in managing personal contact lens care, conventional eye glasses seem safer than corneal contact lenses. Artificial lens implants. Although some infants have had primary intraocular lens implantation at the time of cataract surgery, the associated risk of glaucoma appears higher in those infants with artificial lens implants. Therefore, artificial lens implants should be used with extreme caution, with intraocular pressure carefully monitored (under anesthesia if required) on a continual basis. 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.OtherTo date, no effective treatment for the conjunctival and corneal keloids has been found.Families of affected individuals are often among the most knowledgeable about the problems and needs of their son(s) and must be advocates for them. Interested professionals, families, and other caregivers may contact the Lowe Syndrome Association for literature and additional information.

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. Lowe Syndrome: Genes and DatabasesView in own windowGene SymbolChromosomal LocusProtein NameLocus SpecificHGMDOCRLXq25-q26Inositol polyphosphate 5-phosphatase OCRL-1OCRL @ LOVD at NCBIOCRLData 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 Lowe Syndrome (View All in OMIM) View in own window 300535OCRL GENE; OCRL 309000LOWE OCULOCEREBRORENAL SYNDROME; OCRLMolecular Genetic PathogenesisLowe syndrome results from loss-of-function mutations in OCRL, which encodes for inositol polyphosphate 5-phosphatase OCRL-1 (phosphatidylinositol polyphosphate 5-phosphatase OCRL-1). The enzyme is thought to be involved with regulation of intracellular phosphatidylinositol (4,5) bisphosphate concentration. In an as-yet-unexplained manner, the enzyme deficiency interferes with normal fetal development and postnatal functioning of various organ systems, resulting in the birth defects and other abnormalities found in individuals with Lowe syndrome. Normal allelic variants. The gene contains 5152 nucleotide base pairs and consists of 24 exons, of which 23 are coding. There is also one small (24-bp) alternatively spliced exon, 18a, which encodes an additional eight amino acids and is expressed in neurologic tissues [Nussbaum et al 1997, Nussbaum & Suchy 2001]. Pathologic allelic variants. Many mutations are known. Most are unique to a single family; a few have been noted in more than one unrelated individual. The majority are nucleotide nonsense substitutions or small deletions that result in frameshift and premature termination. Missense mutations and partial or complete genomic deletions also have been reported. Of the identified mutations, 93% have been located in exons 10-18 and exons 19-23 of OCRL, especially in exon 15 [Satre et al 1999, Monnier et al 2000, Nussbaum 2001, Nussbaum & Suchy 2001]. Seven percent of known mutations involve partial or complete genomic deletions [Lin et al 1998, Satre et al 1999, Monnier et al 2000, Nussbaum 2001]. The paucity of detectable mutations in exons 1-9 remains unexplained, but recent data suggest that the frequency of mutations may be increased in the first eight exons of OCRL in Dent disease [Shrimpton et al 2009, Hichri et al 2011]. However, some individuals with Dent-2 are known to have mutations in the 3’ end of OCRL, so there is no perfect correlation between location of mutation within the gene and phenotype [Tosetto et al 2009].Normal gene product. OCRL encodes a 105-kd protein (inositol polyphosphate 5-phosphatase OCRL-1) that has phosphatidylinositol polyphosphate 5-phosphatase activity [Suchy et al 1995, Zhang et al 1995]. The enzyme is present in the trans-Golgi network and the endosomal compartment of a variety of cell types, including brain, skeletal muscle, heart, kidney (cultured proximal renal tubular cells), lung, ovary, testis, cultured fibroblasts, placenta, chorionic villi samples, and cultured amniocytes. It is involved with regulation of intracellular phosphatidylinositol (4,5) bisphosphate concentration and is highly homologous to inositol polyphosphate 5-phosphatase [Nussbaum & Suchy 2001]. Phosphatidylinositol (4,5) bisphosphate is a critical membrane phospholipid that is known to regulate many intracellular processes including protein kinase C activity and intracellular calcium release via its cleavage into diacylglycerol and inositol triphosphate, actin cytoskelon organization, and vesicle trafficking between the endoplasmic reticulum, Golgi, endosomal compartment, and cell surface. PtdIns (4,5) P₂ appears to be involved in the regulation of endocytosis, vesicular formation, and protein trafficking in the Golgi and with actin-cytoskeleton assembly [Vicinanza et al 2008]. Abnormal gene product. Reduced activity or absence of the gene product, inositol polyphosphate 5-phosphatase OCRL-1, leads to elevated intracellular levels of its substrate, phosphatidylinositol (4,5) bisphosphate [PtdIns (4,5) P₂] [Zhang et al 1998]. The loss of inositol polyphosphate 5-phosphatase OCRL-1 causes a defect in intracellular protein trafficking [Vicinanza et al 2011]. Thus, for example, the apical surface protein megalin is markedly reduced both in Lowe syndrome and in Dent disease caused by mutations in CLCN5, suggesting abnormal renal apical epithelial trafficking of this protein [Norden et al 2002]. Actin cytoskeleton organization is also abnormal in fibroblasts from persons with Lowe syndrome [Suchy & Nussbaum 2002]. The OCRL protein product interacts with early and late endosomal proteins, including small G-proteins involved in early to late endosome transition, supporting the model of a defect in endocytosis in Lowe syndrome [Erdmann et al 2007, McCrea et al 2008, Swan et al 2010]. Finally, OCRL-1 has been localized to primary cilia and Lowe syndrome patients’ cells have been reported to show defects in primary cilia assembly and function [Coon et al 2012]. Although the exact mechanisms are unclear, the absence of the protein and elevated PtdIns (4,5) P₂ levels may affect these processes, which may influence cell membrane composition, actin cytoskeletal organization, endocytosis, or all of these in some combination, ultimately leading to abnormal differentiation, cell migration, and function in certain cell types (i.e., renal tubule or lens epithelium). Such changes could result in the birth defects and other clinical manifestations of Lowe syndrome [Zhang et al 1995, Suchy & Nussbaum 2002, Ungewickell et al 2004].