Coats' disease of the retina (unilateral retinal telangiectasis) caused by somatic mutation in the NDP gene: a role for norrin in retinal angiogenesis

Coats' disease is characterized by abnormal retinal vascular development (so-called 'retinal telangiectasis') which results in massive intraretinal and subretinal lipid accumulation (exudative retinal detachment). The classical form of Coats' disease is almost invariably isolated, unilateral and seen in males. A female with a unilateral variant of Coats' disease gave birth to a son affected by Norrie disease. Both carried a missense mutation within the NDP gene on chromosome Xp11.2. Subsequently analysis of the retinas of nine enucleated eyes from males with Coats' disease demonstrated in one a somatic mutation in the NDP gene which was not present within non-retinal tissue. We suggest that Coats' telangiectasis is secondary to somatic mutation in the NDP gene which results in a deficiency of norrin (the protein product of the NDP gene) within the developing retina. This supports recent observations that the protein is critical for normal retinal vasculogenesis.

Three widespread founder mutations contribute to high incidence of X-linked juvenile retinoschisis in Finland

X-linked juvenile retinoschisis (RS) is a recessively inherited disorder causing progressive vitreoretinal degeneration in males. The gene defective in retinoschisis, XLRS1, has recently been identified and characterised. This gene consists of six exons encoding a protein with a putative role in cell-cell adhesion and phospholipid binding. Juvenile retinoschisis has been actively studied in Finland over the past 30 years, with over 300 diagnosed RS patients. Based on genealogical studies, approximately 70% of the Finnish RS patients originate from Western Finland and 20% from Northern Finland. In this study, one third of the known Finnish RS patients were screened for mutations of the XLRS1 gene. Haplotype analysis, using nine microsatellite markers spanning 1 cM in Xp22.2, suggested the segregation of eight different mutations in these families. To identify mutations, the six exons were amplified by PCR and analysed by single strand conformation analysis, followed by direct sequencing of the PCR products. We identified seven distinct missense mutations, all in exons 4 and 6. The mutations in exon 4, 214G > A and 221G > T, are accountable for RS in Western Finland. A third mutation in exon 4, 325G > C, gives rise to RS in Northern Finland. These three founder mutations are the predominant cause of RS in Finland and their existence explains the high incidence of the disease. The identification of mutations common in genetically isolated populations, such as Finland, allows the diagnosis of patients with an atypical RS phenotype and enables nationwide carrier testing and improved genetic counselling.

[Molecular genetics of inherited chorioretinal dystrophy--strategy for identifying disease causing genes]

PURPOSE

To review the strategies for identifying the causative genes of inherited chorioretinal diseases.

METHODS

Three techniques, namely functional cloning, positional cloning, and positional candidate gene approach, have been used for this purpose. Our strategy for identifying the causative genes of inherited chorioretinal diseases is to clone retina-enriched genes, learn their chromosomal map position, and identify their expression in the retina.

RESULTS

In the past 10 years, one gene has been cloned by functional cloning, 9 genes by positional cloning, and 19 genes by the positional candidate gene approach. Our strategy has identified 3 novel genes expressed in the retina, but they have not been associated with chorioretinal diseases.

CONCLUSION

In the next century when the Human Genome Project is finished and the human genome has been sequenced completely, the positional candidate gene approach will become the predominant method of disease gene discovery. The future success of this method is predicated on increasingly dense mapping of the responsible genes by linkage analysis of multiple affected families with inherited chorioretinal diseases.

Idiopathic giant retinal tears in identical twins

PURPOSE

To report idiopathic unilateral giant retinal tears with retinal detachment in identical twins that occurred 2 weeks apart.

METHODS

Case reports.

RESULTS

In both patients, giant retinal tear and retinal detachment was treated with pars plana vitrectomy, placement of encircling scleral buckle, fluid-perfluorocarbon exchange, endolaser treatment, perfluorocarbon-air exchange, and 16% perfluoropropane injection. One year after retinal detachment surgery, cataract developed in both postoperative eyes. Phacoemulsification with posterior chamber intraocular lens implantation was performed on both eyes. Three and a half years after retinal surgery, corrected visual acuity in both treated eyes was 20/20, and retinal reattachment was successful.

CONCLUSIONS

To our knowledge, this is the first report of idiopathic giant retinal tears in identical twins and raises the issue of genetic influences in the pathogenesis of this disease.

Isolated Norrie disease in a female caused by a balanced translocation t(X,6)

This is the second report of Norrie disease in a female patient with a de-novo balanced translocation t(X,6) with breakpoint at the location of the Norrie gene. At the age of 3 months, a girl was referred for suspected congenital glaucoma. The right eye was microphthalmic and ultrasonography was compatible with persistent hyperplasia of the primary vitreous. The left eye was also microphthalmic. The left cornea was larger than the right. The anterior chamber was virtual and leukocoria was evident. The eye felt hard digitally. Ultrasonography indicated an organized retinal detachment. The pathologic findings are reported and are compatible with Norrie disease.

Retinal detachment in an infant with the ring chromosome 13 syndrome

PURPOSE

To inform about retinal detachment in an infant with the ring chromosome 13 as a possible new feature of this syndrome. The finding is able to imitate retinoblastoma, which is closely connected to the deletion of 13q14.

METHODS

We report on a girl with many congenital anomalies including hypoplasia of both optic discs and chorioretinal coloboma of the right eye. Chromosomal analysis revealed karyotype 46 XX with a ring chromosome 13. The patient was examined again at 15 months of age, where leukocoria was disclosed in the left eye, emerging from a retrolental greyish-white mass. Even though neither sonography nor CT showed a typical picture for retinoblastoma, this tumor could not be ruled out. Enucleation of the left eye was performed. The globe was then investigated histopathologically.

RESULTS

No tumor was found in the removed eye. Microscopic examination showed a detached retina with reactive gliosis and neovascularisation.

CONCLUSIONS

The possibility of retinal detachment should be included into differential diagnoses in infants with ring 13 chromosome in cases with a non-specific intraocular mass. The assessment of chromosomal breakpoints in children with this aberration would enable clinicians to determine the real risk of retinoblastoma.

High incidence of autosomal recessive nonsyndromal congenital retinal nonattachment (NCRNA) in an Iranian founding population

In an isolated and founding Iranian population the prevalence of congenital total blindness is 1.1%. Clinical findings such as lack of perception of light, massive retrolental mass, shallow anterior chamber and nystagmus, in otherwise normal individuals, correspond to nonsyndromal congenital retinal nonattachment. To determine the inheritance of this disease we constructed an extensive nine-generation pedigree of the affected kindred living in the Iranian founding population. The pedigree, which includes 42 patients from 25 sibships, clearly suggests autosomal recessive inheritance. To verify the inheritance, we compared the average coefficient of inbreeding (F) of the affected sibships with that of the control sibships, calculated the patients' sex ratio, and also compared the observed relative frequency of the disease with its expected relative frequencies for different modes of inheritance. The patients' average F value is significantly greater than that of the controls (P < 0.001). The sex ratio of the patients is close to unity and the observed relative frequency of the disease is close to that of an autosomal recessive trait. All these findings strongly support autosomal recessive transmission of this disease.

Central nervous system involvement in incontinentia pigmenti: cranial MRI of two siblings

Incontinentia pigmenti is an uncommon neurocutaneous syndrome characterised by skin lesions, dental and ocular abnormalities and central nervous system involvement. We report the cranial MRI findings in two sisters with this condition. These include hypoplasia of the corpus callosum, enlargement of the lateral ventricles and periventricular white-matter lesions. One girl also had unilateral microphthalmia and rostral agenesis of the corpus callosum, a feature not previously described.

[Retinal detachment in Ehlers-Danlos syndrome. Treatment by pars plana vitrectomy]

Ehlers-Danlos syndrome (EDS) is an hereditary connective tissue disorder caused by defective collagen synthesis, the main features being hyperelasticity and vulnerability of the skin, recurrent bleeding from fragile blood vessels, and secondary deformities of the joints. Ocular involvement is a rare occurrence, e.g., corneal and scleral rupture from minor blunt injury, lens displacement, rhegmatogenous retinal detachment. To date, few reports exist concerning the treatment of retinal detachment in Ehlers-Danlos syndrome, all of them dealing exclusively with conventional scleral buckling surgery.

PATIENT AND METHODS

We report on a 47-year-old male patient suffering from EDS type VI (so-called ocular type, lysine-hydroxylase deficiency). He presented with rhegmatogenous retinal detachment in his only eye. A scleral buckling procedure was not feasible because of marked scleral atrophy. A three-port vitrectomy was therefore carried out.

RESULTS

During the operation, pronounced choroidal detachment and bleeding developed, subsiding within weeks postoperatively. Closure of the sclerotomies was difficult due to scleral thinning. Two revitrectomies were necessary because anterior PVR with traction retinal detachment occurred. The last revitrectomy was performed 18 months ago, and the retina has been completely reattached under 5000 cs silicone oil since then. Visual acuity is 0.1.

CONCLUSION

Primary vitrectomy permits successful treatment of retinal detachment in EDS patients if a buckling procedure cannot be performed because of scleral atrophy. However, serious complications may occur. Surgical procedures other than primary vitrectomy should therefore always be carefully considered, e.g., pneumatic retinopexy, temporary balloon, dura patch with episcleral pocket.

Histopathological and immunohistochemical findings associated with a null mutation in the Norrie disease gene

PURPOSE

To determine the clinical, histopathological, and immunohistochemical ocular changes associated with a null mutation in the Norrie disease protein (NDP) gene.

METHODS

Tissue from a six-month-old boy with bilateral retrolental membranes and retinal detachment was obtained during vitreoretinal surgery. Histological sections were stained immunohistochemically with specific antibodies. No eye diseases with severe visual impairment or blindness were reported in the parents and their families. The NDP gene was analyzed by standard molecular genetic methods.

RESULTS

A severe reduction in the number of retinal ganglion cells and a largely disarranged and hypoplastic inner nuclear layer were visible in the tissue specimen. Areas of the tissue with advanced pathology displayed massive fibrovascular proliferation in the vitreous cavity. Shrinkage and traction resulted in folding and detachment of the outer retina. Immunohistochemical reactivity for MIB(1) antigen demonstrated many proliferating cells in the vitreous, but no proliferative activity in the neuroretina. Retinal neurons showed a high grade of differentiation and expressed uniformly neuron-specific enolase and synaptophysin. A 1-base pair insertion (544/545insA) in the NDP gene was found in the affected boy. This mutation predicts a 'functional null-allele' due to a shift in the reading frame and, thus, a premature termination of mRNA translation after 55 instead of 133 amino acids.

CONCLUSIONS

Loss of function of the NDP gene causes marked hypoplasia of the inner retinal cell layers and fibrovascular proliferation in the vitreous cavity, leading to retinal folding and detachment. The NDP therefore seems to play a critical role in terminal differentiation of the inner retinal cell layers and establishment and maintaining of anti-proliferative cellular interactions in the vitreous.

Norrie disease in a family with a manifesting female carrier

OBJECTIVES

To show that Norrie disease can occur in a girl and to describe her ophthalmologic and genetic features.

METHODS

Amplification of DNA polymerase chain reaction and sequencing of asymmetric polymerase chain reaction for exon 3 were performed on the blood specimen obtained from a girl born with bilateral retinal detachments.

PATIENT

A female child with bilateral retinal detachment who had 2 uncles in whom Norrie disease had already been diagnosed.

RESULTS

The child had a mutation in the third exon (T776-->A; Ile 123-->Asn) identical to the mutation found in her uncles.

CONCLUSIONS

Norrie disease can occur in girls. The most likely explanation is nonrandom or unfavorable X inactivation, although timing of development of the peripheral retina and its blood supply could render it vulnerable to effects of the mutant allele at a critical developmental phase.

[Rhegmatogenous retinal detachment in atrophia gyrata: pars plana vitrectomy with silicone oil instillation]

BACKGROUND

Gyrate atrophy is a form of choroidal dystrophia characterized by a genetic defect of the mitochondrial matrix enzyme ornithine ketoacidoaminotransferase on chromosome 10. Apart from rare myopathic problems, cases of choroidal, iridal atrophy, complicated subcapsular cataract, optic atrophy, macular edema, reticular retinoschisis, vasculitis and perivasculitis could be observed so far. To our knowledge, rheumatogenous retinal detachment has been described before. We present a 34-year-old female subject with a retinal detachment of the right eye over 3 quadrants with 3 small round foramina in the area 10 to 11 o'clock.

PATIENTS

Concentric defects of the visual field had been known since the age of 4; the patient was slightly myopic. At the age of 31, the patient had undergone cataract extraction with implantation of posterior chamber lenses in both eyes. The ophthalmological examination revealed large areas of choroidal atrophia in both eyes. A determination of visual acuity resulted in hand movements in the right eye and 0.1 in the left eye. The ERG was extinguished.

RESULTS

The retina could be fully reattached by pars plana vitrectomy and instillation of silicone oil. At the same time, we performed an excision of secondary cataract. On demission, the visual acuity of the right eye was finger counting. Because a brother of the patient had also suffering from a progressive choroidal atrophy since his childhood, an autosomal recessive disease was suspected. The only abnormality detected was strongly elevated plasma levels of ornithin (7.5 to 14 mg/dl, compared to levels of 0.6 to 2.0 in controls). Urinary excretion of ornithin was also strongly increased.

DISCUSSION

To our knowledge there was no previous description of a case of atrophia gyrata in association with rhegmatogenous retinal detachment after intraocular surgery. As the pigment epithelium is missing, intraoperative endolaser-coagulation would be useless. For this reason, and since a tendency for reattachment is lacking consistent with one of the characteristics of this disease, the only approach to this case is intraocular tamponade with silicone oil.

Norrie disease. Diagnosis of a simplex case by DNA analysis

Norrie disease is a rare, X-linked recessive disorder characterized by congenital blindness due to malformed retinas. We describe a simplex patient who had leukokoria and whose clinical diagnosis was confirmed only after molecular genetics analysis. DNA analysis was also used to determine the carrier status of relatives of the proband.

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.

A-2-->G transition at the 3' acceptor splice site of IVS17 characterizes the COL2A1 gene mutation in the original Stickler syndrome kindred

Hereditary progressive arthro-ophthalmopathy, or "Stickler syndrome," is an autosomal dominant osteochondrodysplasia characterized by a variety of ocular and skeletal anomalies which frequently lead to retinal detachment and precocious osteoarthritis. A variety of mutations in the COL2A1 gene have been identified in "Stickler" families; in most cases studied thus far, the consequence of mutation is the premature generation of a stop codon. We report here the characterization of a COL2A1 gene mutation in the original kindred described by Stickler et al. [1965]. Conformational sensitive gel electrophoresis (CSGE) [Ganguly et al., 1993] was used to screen for mutations in the entire COL2A1 gene in an affected member from the kindred. A prominent heteroduplex species was noted in the polymerase chain reaction (PCR) product from a region of the gene including exons 17 to 20. Direct sequencing of PCR-amplified genomic DNA resulted in the identification of a base substitution at the A-2 position of the 3' splice acceptor site of IVS17. Sequencing of DNA from affected and unaffected family members confirmed that the mutation segregated with the disease phenotype. Reverse transcriptase-PCR analysis of poly A+ RNA demonstrated that the mutant allele utilized a cryptic splice site in exon 18 of the gene, eliminating 16 bp at the start of exon 18. This frameshift eventually results in a premature termination codon. These findings are the first report of a splice site mutation in classical Stickler syndrome and they provide a satisfying historical context in which to view COL2A1 mutations in this dysplasia.

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.

[Uveal effusion syndrome: clinical and ultrastructural aspects]

Spontaneous serous detachment of the choroid and ciliary body, together with bullous serous detachment of the retina (uveal effusion syndrome) is a rare but well-defined syndrome frequently associated with nanophthalmos.

CASE REPORTS

Based on three cases whose one familial, clinical and ultrastructural characteristics of the syndrome are reviewed and the role of ultrasonic biomicroscopy (UBM) presented.

CONCLUSION

The severe and potentially blinding complications encountered after any surgery on these eyes make the recognition of the classical clinical signs and symptoms of the syndrome particularly important. In this context, UBM represents an interesting new tool in terms of diagnosis and pathophysiology understanding.

Hereditary vitreopathy

Heterogeneity has long been recognised within the spectrum of inherited vitreo-retinal disease but the extent of the variation has been less easy to quantify. This has been compounded by the small size and numbers of pedigrees available for the study, and the phenotypic variation both within and between pedigrees. Formation abnormalities in the vitreous architecture have, in the past, been eclipsed by classifications based on general skeletal and morphological differences. Stickler syndrome is the commonest disorder within the spectrum of hereditary vitreous abnormalities and many of the recent published advances relate to this. Stickler syndrome has been subclassified on the basis of vitreo-retinal phenotype: type 1 families with a characteristic congenital vitreous anomaly show linkage without recombination to markers at the COL2A1 locus; type 2 families with different congenital vitreo-retinal phenotypes are not linked to COL2A1. A recent report identifies the COL11A2 mutation in a Dutch pedigree with systemic features of Stickler syndrome but without ocular involvement. Others have implicated COL11A1 in a type 2 Stickler syndrome pedigree with ocular abnormalities. Both COL11A1 and COL11A2 are expressed in cartilage, but on the basis of studies of bovine vitreous it is likely that only the alpha 1(XI) chain encoded by COL11A1 is present in vitreous. This would be consistent with the hypothesis that mutations in the genes encoding collagen XI can give rise to manifestations of Stickler syndrome, but of these, only mutations in COL11A1 will give the full syndrome including the vitreo-retinal features.

Stickler syndrome. A mutation in the nonhelical 3' end of type II procollagen gene

BACKGROUND

All of the mutations in the type II procollagen (COL2A1) gene that have been identified in families affected with Stickler syndrome have been located primarily in the triple helical region of the gene. We report what we believe is the first premature stop codon in the globular C-propeptide region encoded by the COL2A1 gene, in a family affected with Stickler syndrome.

DESIGN

Genomic DNA from affected and unaffected family members of this three-generation family was amplified using the polymerase chain reaction. The polymerase chain reaction products were directly sequenced for DNA analysis.

RESULTS

Direct sequencing showed a single base deletion in exon 50, resulting in a premature stop codon in exon 51 in the globular C-propeptide of COL2A1 gene in all affected members.

CONCLUSIONS

These results implicate premature stop codons as a common cause of Stickler syndrome. The location of this premature stop codon in the far end of the nonhelical 3' end of the gene indicates that a truncated C-propeptide of at least 84 amino acid residues is inadequate for the functional gene product.