Missense mutation (Arg121Trp) in the Norrie disease gene associated with x-linked exudative vitreoretinopathy

Genotype-Phenotype Characterization of Novel Variants in Six Italian Patients with Familial Exudative Vitreoretinopathy

Familial exudative vitreoretinopathy (FEVR) is a complex disorder characterized by incomplete development of the retinal vasculature. Here, we report the results obtained on the spectrum of genetic variations and correlated phenotypes found in a cohort of Italian FEVR patients. Eight probands (age range 7–19 years) were assessed by genetic analysis and comprehensive age-appropriate ophthalmic examination. Genetic testing investigated the genes most widely associated in literature with FEVR: FZD4, LRP5, TSPAN12, and NDP. Clinical and genetic evaluations were extended to relatives of probands positive to genetic testing. Six out of eight probands (75%) showed a genetic variation probably related to the phenotype. We identified four novel genetic variants, one variant already described in association with Norrie disease and one previously described linked to autosomal dominant FEVR. Pedigree analysis of patients led to the classification of four autosomal dominant cases of FEVR (caused by FZD4 and TSPAN12 variants) and two X-linked FEVR probands (NDP variants). None of the patients showed variants in the LRP5 gene. This study represents the largest cohort study in Italian FEVR patients. Our findings are in agreement with the previous literature confirming that FEVR is a clinically and genetically heterogeneous retinal disorder, even when it manifests in the same family.

Novel and recurrent NDP gene mutations in familial cases of Norrie disease and X-linked exudative vitreoretinopathy

PURPOSE

To present the results of molecular analysis of the NDP gene in Mexican families with Norrie disease (ND) and X-linked familial exudative vitreoretinopathy (XL-FEVR).

METHODS

Two unrelated families with ND and two with XL-FEVR were studied. Clinical diagnosis was suspected on the basis of a complete ophthalmologic examination. Molecular methods included DNA isolation from peripheral blood leucocytes, polymerase chain reaction amplification and direct nucleotide sequencing analysis of the complete coding region and exon-intron junctions of NDP. Haplotype analysis using NDP-linked microsatellites markers was performed in both ND families.

RESULTS

A novel Norrin missense mutation, p.Arg41Thr, was identified in two apparently unrelated families with ND. Haplotype analysis demonstrated that affected males in these two families shared the same ND-linked haplotype, suggesting a common origin for this novel mutation. The previously reported p.Arg121Trp and p.Arg121Gln Norrin mutations were identified in the two families with XL-FEVR.

CONCLUSION

Our results expand the mutational spectrum in ND. This is the first report of ND resulting from mutation at arginine position 41 of Norrin. Interestingly, mutations at the same residue but resulting in a different missense change were previously described in subjects with XL-FEVR (p.Arg41Lys) or persistent fetal vasculature syndrome (p.Arg41Ser), indicating that the novel p.Arg41Thr change causes a more severe retinal phenotype. Preliminary data suggest a founder effect for the ND p.Arg41Thr mutation in these two Mexican families.

Genetic Evaluation to Establish the Diagnosis of X-Linked Familial Exudative Vitreoretinopathy

PURPOSE

To determine the usefulness of genetic analysis for confirming the diagnosis of X-linked familial exudative vitreoretinopathy (FEVR) and verifying the mode of inheritance.

METHODS

Twenty-seven consecutive patients diagnosed with FEVR were enrolled for genetic analysis. All patients underwent dilated fundus examination. A complete birth, medical, and family history was obtained at the time of examination. Patients were categorized by gender and family history in an effort to identify X-linked FEVR. Participants provided a blood sample for analysis and were evaluated for a mutation in the Norrie's disease gene (NDP) by direct sequencing.

RESULTS

Of the 27 enrolled patients, four male patients had a pedigree consistent with X-linked inheritance and 12 male patients had little or no family history. Two of these 16 patients were found to have a missense mutation in the NDP gene.

CONCLUSIONS

We found genetic testing of NDP to be helpful in confirming the diagnosis of X-linked FEVR in male patients, especially when limited family history was available. As genetic diagnostics improve, we feel that confirming diagnoses and informing patients better through genetic evaluation and consultation will become more useful in the clinical practice of ophthalmology.

Norrie-Warburg syndrome: two novel mutations in patients with classical clinical phenotype

Norrie-Warburg syndrome (NWS) is a rare X-linked disorder characterized by blindness, which is invariable, deafness and mental disturbances, which are present occasionally. We describe here two novel mutations, a missense mutation (C126S) and a 1-base pair insertion (insT466/T467), together with a recurrent mutation (M1V), found in patients presenting with the classical clinical phenotype of NWS. All three mutations are likely to result in prominent structural changes of the norrin protein.

SNPs: impact on gene function and phenotype

Single nucleotide polymorphism (SNP) is the simplest form of DNA variation among individuals. These simple changes can be of transition or transversion type and they occur throughout the genome at a frequency of about one in 1,000 bp. They may be responsible for the diversity among individuals, genome evolution, the most common familial traits such as curly hair, interindividual differences in drug response, and complex and common diseases such as diabetes, obesity, hypertension, and psychiatric disorders. SNPs may change the encoded amino acids (nonsynonymous) or can be silent (synonymous) or simply occur in the noncoding regions. They may influence promoter activity (gene expression), messenger RNA (mRNA) conformation (stability), and subcellular localization of mRNAs and/or proteins and hence may produce disease. Therefore, identification of numerous variations in genes and analysis of their effects may lead to a better understanding of their impact on gene function and health of an individual. This improved knowledge may provide a starting point for the development of new, useful SNP markers for medical testing and a safer individualized medication to treat the most common devastating disorders. This will revolutionize the medical field in the future. To illustrate the effect of SNPs on gene function and phenotype, this minireview focuses on evidences revealing the impact of SNPs on the development and progression of three human eye disorders (Norrie disease, familial exudative vitreoretinopathy, and retinopathy of prematurity) that have overlapping clinical manifestations.

Mutations in the NDP gene: contribution to Norrie disease, familial exudative vitreoretinopathy and retinopathy of prematurity

BACKGROUND

To examine the contribution of mutations within the Norrie disease (NDP) gene to the clinically similar retinal diseases Norrie disease, X-linked familial exudative vitreoretinopathy (FEVR), Coat's disease and retinopathy of prematurity (ROP).

METHODS

A dataset comprising 13 Norrie-FEVR, one Coat's disease, 31 ROP patients and 90 ex-premature babies of <32 weeks' gestation underwent an ophthalmologic examination and were screened for mutations within the NDP gene by direct DNA sequencing, denaturing high-performance liquid chromatography or gel electrophoresis. Controls were only screened using denaturing high-performance liquid chromatography and gel electrophoresis. Confirmation of mutations identified was obtained by DNA sequencing.

RESULTS

Evidence for two novel mutations in the NDP gene was presented: Leu103Val in one FEVR patient and His43Arg in monozygotic twin Norrie disease patients. Furthermore, a previously described 14-bp deletion located in the 5' unstranslated region of the NDP gene was detected in three cases of regressed ROP. A second heterozygotic 14-bp deletion was detected in an unaffected ex-premature girl. Only two of the 13 Norrie-FEVR index cases had the full features of Norrie disease with deafness and mental retardation.

CONCLUSION

Two novel mutations within the coding region of the NDP gene were found, one associated with a severe disease phenotypes of Norrie disease and the other with FEVR. A deletion within the non-coding region was associated with only mild-regressed ROP, despite the presence of low birthweight, prematurity and exposure to oxygen. In full-term children with retinal detachment only 15% appear to have the full features of Norrie disease and this is important for counselling parents on the possible long-term outcome.

Differential prioritization between relevance and redundancy in correlation-based feature selection techniques for multiclass gene expression data

BACKGROUND

Due to the large number of genes in a typical microarray dataset, feature selection looks set to play an important role in reducing noise and computational cost in gene expression-based tissue classification while improving accuracy at the same time. Surprisingly, this does not appear to be the case for all multiclass microarray datasets. The reason is that many feature selection techniques applied on microarray datasets are either rank-based and hence do not take into account correlations between genes, or are wrapper-based, which require high computational cost, and often yield difficult-to-reproduce results. In studies where correlations between genes are considered, attempts to establish the merit of the proposed techniques are hampered by evaluation procedures which are less than meticulous, resulting in overly optimistic estimates of accuracy.

RESULTS

We present two realistically evaluated correlation-based feature selection techniques which incorporate, in addition to the two existing criteria involved in forming a predictor set (relevance and redundancy), a third criterion called the degree of differential prioritization (DDP). DDP functions as a parameter to strike the balance between relevance and redundancy, providing our techniques with the novel ability to differentially prioritize the optimization of relevance against redundancy (and vice versa). This ability proves useful in producing optimal classification accuracy while using reasonably small predictor set sizes for nine well-known multiclass microarray datasets.

CONCLUSION

For multiclass microarray datasets, especially the GCM and NCI60 datasets, DDP enables our filter-based techniques to produce accuracies better than those reported in previous studies which employed similarly realistic evaluation procedures.

Retinopathy of prematurity: recent advances in our understanding

Retinopathy of prematurity (ROP) has been recognised as an important cause of childhood visual impairment and blindness since the 1940s when improved facilities and treatment increased the survival rate of premature infants. Although its incidence and severity have been decreasing in developed countries over the past two decades, both are increasing in developing nations. ROP is consequently targeted as an important but avoidable disease. This review provides an updated summary and discussion of much of the work that has been produced through population, animal, cell culture, and genetic research. The authors examine the prevalence, risk factors, and possible causes of the disease with a particular focus on genetic studies. They conclude that while significant reductions in the disease have occurred in developed countries, further research is required to fully understand and prevent the disease. In the meantime, development and implementation of appropriate screening and treatment strategies will be critical in reducing blindness in developing countries.

Vascular defects and sensorineural deafness in a mouse model of Norrie disease

Norrie disease is an X-linked recessive syndrome of blindness, deafness, and mental retardation. A knock-out mouse model with an Ndp gene disruption was studied. We examined the hearing phenotype, including audiological, histological, and vascular evaluations. As is seen in humans, the mice had progressive hearing loss leading to profound deafness. The primary lesion was localized to the stria vascularis, which houses the main vasculature of the cochlea. Fluorescent dyes showed an abnormal vasculature in this region and eventual loss of two-thirds of the vessels. We propose that one of the principal functions of norrin in the ear is to regulate the interaction of the cochlea with its vasculature.

A C597-->A polymorphism in the Norrie disease gene is associated with advanced retinopathy of prematurity in premature Kuwaiti infants

Retinopathy of prematurity (ROP) is a retinal vascular disease which occurs in infants with a short gestational age and low birth weight and may lead to retinal detachment and blindness. In some premature infants, ROP progresses to advanced stages despite rigorous intervention, but in the majority, it spontaneously regresses before the threshold stage. Genetic factors, e.g. mutations in the Norrie disease (ND) gene, have been implicated in determining the progression of ROP to advanced stages. We have identified a novel C597A polymorphism of the ND gene; we screened this and another mutation in the ND gene, C110G, in 210 premature Kuwaiti infants using PCR-RFLP, DNA sequence analysis and DNA enzyme immunoassay hybridization to investigate their association with advanced-stage ROP. In this cohort of premature Kuwaiti newborns, 115 of 210 babies had no eye problems and served as controls, while 95 were found to have ROP. In 71 of the 95 ROP cases, the disease spontaneously regressed at or before stage 3, while in 24 of 95 ROP cases, the disease progressed to advanced stages 4 or 5. The incidence of the AA genotype of the C597A polymorphism was considerably higher in advanced-stage ROP cases (83.3%) compared to spontaneously regressing ROP cases (0%) and the normal controls (10.4%) (p < 0.0001). For the other genotypes, no significant difference was detected between the controls and ROP cases. In the case of the C110G mutation in the ND gene, no significant differences were detected between the controls and ROP cases, and the majority of subjects had a CC genotype in all three groups.

Retinopathy of prematurity: recent advances in our understanding

Retinopathy of prematurity (ROP) has been recognised as an important cause of childhood visual impairment and blindness since the 1940s when improved facilities and treatment increased the survival rate of premature infants. Although its incidence and severity have been decreasing in developed countries over the past two decades, both are increasing in developing nations. ROP is consequently targeted as an important but avoidable disease. This review provides an updated summary and discussion of much of the work that has been produced through population, animal, cell culture, and genetic research. The authors examine the prevalence, risk factors, and possible causes of the disease with a particular focus on genetic studies. They conclude that while significant reductions in the disease have occurred in developed countries, further research is required to fully understand and prevent the disease. In the meantime, development and implementation of appropriate screening and treatment strategies will be critical in reducing blindness in developing countries.

Identification of novel missense mutations in the Norrie disease gene associated with one X-linked and four sporadic cases of familial exudative vitreoretinopathy

X-linked Familial Exudative Vitreoretinopathy (XLFEVR) is a hereditary eye disorder that affects both the retina and the vitreous body. It is characterized by an abnormal vascularization of the peripheral retina. It has been previously shown by linkage and candidate gene analysis that XLFEVR and Norrie disease are allelic. In this report we describe four novel mutations (R41K, H42R, K58N, and Y120C) in the Norrie disease gene associated with one X-linked and four sporadic cases of FEVR. One mutation (H42R) was found to be segregating with the disease in three generations (X-linked family), and the others are sporadic. These sequence alterations changed the encoded amino acids in the Norrie disease protein and were not found in 17 unaffected family members or in 36 randomly selected normal individuals. This study provides additional evidence that mutations in the same gene can result in FEVR and Norrie disease. It also demonstrates that it may be beneficial for clinical diagnosis to screen for mutations in the Norrie disease gene in sporadic FEVR cases.

A novel mutation in the Norrie disease gene

Norrie disease is an X-linked recessive disorder characterized by congenital blindness and in some cases mental retardation and deafness.(1) The variability of signs among patients often complicates diagnosis. Signs such as an ocular pseudoglioma, progressive deafness, and mental disturbance are considered classic features.(2) Only one third of patients with Norrie disease have sensorineural deafness, and approximately one half of the affected individuals exhibit mental retardation, often with psychotic features.(3) Histologic analysis has suggested that retinal dysgenesis occurs early in eye development and involves cells in the inner wall of the optic cup.(4) The gene associated with Norrie disease was identified in 1992. (5,6) We report a novel mutation identified in a patient in whom Norrie disease was diagnosed.

Localization of the Norrie disease gene mRNA by in situ hybridization

Norrie disease is a rare X-linked recessive neurodevelopmental disorder. The affected males manifest congenital blindness, which is often associated with hearing loss, mental retardation and psychiatric problems. Genetic linkage studies have localized the gene to the short arm of the X-chromosome and the gene has been isolated recently. The encoded protein is a member of the superfamily of growth factors containing a cystine knot motif and may be involved in cell adhesion and neurodevelopment. Molecular genetic analysis revealed a large number of missense, nonsense, deletion, and splice-site mutations among Norrie patients. In order to further determine the role of the Norrie disease gene, we studied the distribution pattern of its mRNA in the retina and in brain by in situ hybridization. The results show abundant hybridization signals in outer nuclear, inner nuclear, and ganglion cell layers of the retina in all three species (mice, rabbit, and human) examined. There was no significant expression in the vitreous body, lens, and rod outer segment. High expression levels were also observed in the cerebellar granular layer, hippocampus, olfactory bulb, cortex, and epithelium of the rabbit brain. These data suggest that the Norrie disease gene could play a critical role in the differentiation or maintenance of the differentiated state of the retina.

Norrie disease and exudative vitreoretinopathy in families with affected female carriers

PURPOSE

Norrie disease (ND) is a rare X-linked recessive disorder characterized by congenital blindness, which is often associated with sensorineural hearing loss and mental retardation. X-linked familial exudative vitreoretinopathy (FEVR) is a hereditary disorder characterized by an abnormality of the peripheral retina and is not associated with systemic diseases. X-linked recessive disorders generally do not affect females. Here we show that female carriers can be associated with manifestation of an X-linked disorder.

METHODS

A four-generation family with an affected female, and a history of congenital blindness and hearing loss, was identified through the pro-band. A second family, with a full-term female infant, was evaluated through ophthalmic examinations and found to exhibit ocular features, such as retinal folds, retinal detachment and peripheral exudates. Peripheral blood specimens were collected from several affected and unaffected family members. DNA was extracted and analyzed by single-strand conformation polymorphism (SSCP) following polymerase chain reaction (PCR) amplification of the exons of the Norrie disease gene. The amplified products were sequenced by the dideoxy chain termination method.

RESULTS

In an X-linked four-generation family, a novel missense (A118D) mutation in the third exon of the Norrie disease gene, was identified. The mutation was transmitted through three generations and cosegregated with the disease. The affected maternal grandmother and the unaffected mother carried the same mutation in one of their alleles. In an unrelated sporadic family, a heterozygous missense mutation (C96Y) was identified in the third exon of the Norrie disease gene in an affected individual. Analysis of exon-1 and 2 of the Norrie disease gene did not reveal any additional sequence alterations in these families. The mutations were not detected in the unaffected family members and the 116 normal unrelated controls, suggesting that they are likely to be the pathogenic mutations.

CONCLUSIONS

The results further strengthen the proposal that X-linked disorders can occur in female carriers, due likely to an unfavorable X-inactivation.

Identification of a recurrent missense mutation in the Norrie disease gene associated with a simplex case of exudative vitreoretinopathy

Disorders such as Norrie disease, X-linked familial exudative vitreoretinopathy, retinopathy of prematurity and X-linked primary vitreoretinal dysplasia have very similar clinical manifestations. They exhibit retinal fold, retinal detachment, retinal traction and the formation of retrolental fibrovascular membrane. In order to identify carriers for these disorders and provide precise genetic counseling of the relatives, a molecular genetic analysis will be helpful. This report describes the results of Norrie disease analysis in simplex cases of exudative vitreoretinopathy. the identification of a recurrent mutation in the Norrie disease gene in a simplex case of exudative vitreoretinopathy further strengthens the notion that Norrie disease and exudative vitreoretinopathy are allelic disorders.

Norrie disease protein (norrin) forms disulfide-linked oligomers associated with the extracellular matrix

COS-7 cells transfected with a DNA construct encoding the 133 amino acids in norrin plus six histidine residues at its carboxyl terminus were pulse-labeled with [35S]cysteine, and the labeled norrin was examined in cell lysates, the medium, and the extracellular matrix. SDS-gel electrophoresis under reducing conditions showed that the norrin expressed had an apparent Mr = 14,000 and was present only in cell lysates and the extracellular matrix. Under nonreducing conditions, most of the norrin in the extracellular matrix was oligomers that contained up to approximately 20 monomers. One of the major extracellular species of norrin under reducing conditions after cross-linking of norrin oligomers with bis(sulfosuccinimidyl)suberate had an apparent Mr = 28,000, consistent with covalent cross-linked dimers. Thus the covalently cross-linked dimers are key structural components of norrin oligomers. By site-directed mutagenesis, the codon for half-cystine 95 in norrin was changed to one encoding alanine. The norrin C95A found in the extracellular matrix of cells transfected with this mutant was the size of dimers, indicating that half-cystine 95 is involved in oligomer formation. The corresponding half-cystine residue in human prepro-von Willebrand factor is also involved in interchain disulfide bond formation, which is consistent with the sequence identity of the half-cystine residues in norrin and part of the half-cystine residues in a disulfide-rich domain of von Willebrand factor. Replacement of valine at residue 60 in norrin by glutamic acid, a mutation found in humans with a severe type of Norrie disease, results in a considerable reduction (50%) in the amount of norrin in the extracellular matrix of transfected COS-7 cells. Replacement of arginine at residue 121 by glutamine, which is associated with a less severe type of Norrie disease, results in a reduction in the amount of norrin R121Q in the extracellular matrix (26%). These studies suggest that norrin is a secreted protein that forms disulfide-bonded oligomers that are associated with the extracellular matrix upon secretion from cells. Moreover, the disulfide-rich motif of norrin and prepro-von Willebrand factor promotes interchain disulfide bond formation among polypeptides in which it is found.

Two novel mutations in the Norrie disease gene associated with the classical ocular phenotype

Norrie disease (ND) is a rare X-linked recessive disorder characterized by congenital blindness due to a degenerative and proliferative dysplasia of the neuroretina and, occasionally, by deafness and mental handicap. Here, we report two novel mutations detected in patients with the classical eye features of ND. Both the one-base pair insertion in exon II (544/545 insA) and the two-base pair deletion in the start codon (418delTG) of the ND gene predict a functional 'null allele', i.e. the complete absence of the corresponding gene product.

Peripheral retinopathy in offspring of carriers of Norrie disease gene mutations. Possible transplacental effect of abnormal Norrin

BACKGROUND

The Norrie disease (ND) gene (Xp11.3) (McKusick 310600) consists of one untranslated exon and two exons partially translated as the Norrie disease protein (Norrin). Norrin has sequence homology and computer-predicted tertiary structure of a growth factor containing a cystine knot motif, which affects endothelial cell migration and proliferation. Norrie disease (congenital retinal detachment), X-linked primary retinal dysplasia (congenital retinal fold), and X-linked exudative vitreoretinopathy (congenital macular ectopia) are allelic disorders.

METHODS

Blood was drawn for genetic studies from members of two families to test for ND gene mutations. Sixteen unaffected family members were examined ophthalmologically. If any retinal abnormality were identified, fundus photography and fluorescein angiography was performed.

RESULTS

Family A had ND (R109stp), and family B had X-linked exudative vitreoretinopathy (R121L). The retinas of 11 offspring of carrier females were examined: three of seven carrier females, three of three otherwise healthy females, and one of one otherwise healthy male had peripheral inner retinal vascular abnormalities. The retinas of five offspring of affected males were examined: none of three carrier females and none of two otherwise healthy males had this peripheral retinal finding.

CONCLUSIONS

Peripheral inner retinal vascular abnormalities similar to regressed retinopathy of prematurity were identified in seven offspring of carriers of ND gene mutations in two families. These ophthalmologic findings, especially in four genetically healthy offspring, strongly support the hypothesis that abnormal Norrin may have an adverse transplacental (environmental) effect on normal inner retinal vasculogenesis.

X-linked exudative vitreoretinopathy caused by an arginine to leucine substitution (R121L) in the Norrie disease protein

We report the cosegregation of an arginine to leucine substitution at position 121 of the Norrie disease protein in a large kindred where exudative vitreoretinopathy segregates as an X-linked recessive trait. The clinical phenotype and rate of disease progression were extremely variable, with progression to total retinal detachment from less than age 2 years to more than 21 years. To date, all mutations in X-linked vitreoretinopathy have been missense mutations, presumably not affecting the three-dimensional structure of the NDP gene product, and clustered around residues 121-126 of the Norrie protein. This contrasts with the diversity of mutations seen in the more severe, allelic Norrie disease.

Retinopathy of prematurity in infants of birth weight > 2000 g after haemorrhagic shock at birth

BACKGROUND

The risk of retinopathy of prematurity (ROP) is associated with low birth weight and low gestational age. For ROP screening examination is recommended in infants weighing < or = 1500 g or of less than 32 weeks' gestational age.

METHODS

From 1991 ROP screening was performed in 452 premature infants with either a birth weight < or = 1500 g (n = 303) or a birth weight > 1500 g (n = 149) and who required additional oxygen supplementation or underwent surgery with general anaesthesia before estimated term.

RESULTS

Unexpectedly, three infants with birth weights between 2080 and 2325 g and a gestational age of 32 or 33 weeks developed stage 2 or 3 ROP. One of these underwent cryocoagulation. In three infants, preterm birth was induced by sudden placental abruption with severe prenatal blood loss followed by haemorrhagic shock. The umbilical cord packed cell volume was reduced to 0.14-0.19 (normal 0.43-0.63). All three infants underwent surgery with general anaesthesia within the first weeks of life. Of the remaining 449 infants none with a birth weight > 1650 g developed any stage of ROP.

CONCLUSION

Severe prenatal blood loss requiring blood transfusions and surgery with general anaesthesia may induce higher stages of ROP even in infants with birth weights exceeding the usual screening criteria.

Ocular phenotypes associated with two mutations (R121W, C126X) in the Norrie disease gene

PURPOSE

To describe the ocular phenotypes associated with 2 mutations in the Norrie disease gene including a manifesting carrier.

METHODS

Ophthalmological examinations were performed in 2 affected males and one manifesting carrier. Genomic DNA was analyzed by direct sequencing of the Norrie disease gene.

RESULTS

Family I: A 29-year-old male had the right eye enucleated at the age of 3 years. His left eye showed severe temporal dragging of the retina and central scars. Visual acuity was 20/300. DNA analysis revealed a C-to-T transition of the first nucleotide in codon 121 predicting the replacement of arginine-121 by tryptophan (R121W). Both the mother and maternal grandmother carry the same mutation in heterozygous form. Family 2: A 3-month-old boy presented with severe temporal dragging of the retina on both eyes and subsequently developed retinal detachment. Visual acuity was limited to light perception. His mother's left eye was amaurotic and phthitic. Her right eye showed severe retinal dragging, visual acuity was reduced to 20/60. DNA analysis revealed a T-to-A transversion of the third nucleotide in codon 126 creating a stop codon (C126X). The mother and maternal grandmother were carriers.

CONCLUSION

Mutations in the Norrie disease gene can lead to retinal malformations of variable severity both in hemizygous males and manifesting carriers.