Miki Hiraoka

Insertion and deletion mutations in the dinucleotide repeat region of the Norrie disease gene in patients with advanced retinopathy of prematurity

AbstractRetinopathy of prematurity (ROP) is a leading cause of blindness in premature children. It is a multifactorial disorder which causes fibrovascular tissue changes that affect the retina in low birth-weight and short gestational age infants. To determine the prevalence of Norrie disease (ND) gene mutations, clinical examination and molecular genetic analyses were performed in 100 pre-term babies of different ethnic backgrounds who developed advanced ROP. The leukocyte DNA was extracted, amplified by the polymerase chain reaction (PCR), and analyzed by single-strand conformation polymorphism (SSCP), G/T and C/A scanning, and by DNA sequencing. All three exons, including splice sites and the 3′-untranslated region, were screened. Of the 100 patients analyzed, 2 patients with advanced ROP showed a mobility shift in the DNA. In 1 patient, this mobility shift was caused by the insertion of an additional 12-bp CT repeat in exon 1, and in the second patient, there was a 14-bp deletion in the same exon of the ND gene, as evidenced by direct sequencing of the amplified products. Similar analyses of exons 2 and 3 and the 3′-untranslated region failed to detect additional mutations in the gene. None of the 130 normal, unrelated controls revealed similar changes. Taking into account the above results, as well as those of other studies, it appears that the ND gene mutations can account for 3% of cases of advanced ROP. Although the ND gene is not frequently involved in advanced ROP, the present large-scale study further supports the hypothesis that genetic influences may play an important role in the development of severe ROP in some premature infants.

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 (SS-CP) 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.

Coats’ Disease and Congenital Retinoschisis in a Single Eye: A Case Report and DNA Analysis

The clinical features of Coats’ disease and congenital retinoschisis (RS) are distinctly different. Therefore, finding changes consistent with Coats’ disease and congenital RS in a single eye is an unusual occurrence. The following report describes two cases with a Coats’ telangiectatic lesion in one region of the retina separated by normal retina and the presence of central and peripheral congenital RS. Molecular genetic analysis of the Norrie disease and RS genes failed to identify disease-causing or polymorphic mutations in either of the genes, suggesting that the above condition is clinically and genetically a different disorder. Further studies are needed to identify the genes responsible for the above disorder and associated ocular manifestations.

X-linked juvenile retinoschisis: mutations at the retinoschisis and Norrie disease gene loci?

AbstractJuvenile retinoschisis (RS) and Norrie disease (ND) are X-linked recessive retinal disorders. Both disorders, in the majority of cases, are monogenic and are caused by mutations in the RS and ND genes, respectively. Here we report the identification of a family in which mutations in both the RS and ND genes are segregating with RS pathology. Although the mutations identified in this report were not functionally characterized with regard to their pathogenicity, it is likely that both of them are involved in RS pathology in the family analyzed. This suggests the complexity and digenic nature of monogenic human disorders in some cases. If this proves to be a widespread problem, it will complicate the strategies used to identify the genes involved in diseases and to develop methods for intervention.

Lack of association of the Norrie disease gene with retinoschisis phenotype.

PURPOSE It has been reported recently that mice carrying a disrupted Norrie disease gene produced alterations in the murine eye that are similar to congenital retinoschisis. Therefore, it was of interest to determine whether mutations in the Norrie disease gene can account for the disease in families with retinoschisis that do not carry mutations in the retinoschisis gene. METHODS The patient set comprised 5 cases of retinoschisis (1 familial and 4 sporadic), all unrelated to each other. Fundus examination of affected individuals showed foveal and peripheral schisis, and the visual acuity range was 20/40-20/60. Peripheral blood specimens were collected from affected and unaffected family members. DNA was extracted and amplified by polymerase chain reaction amplification of exons of the Norrie disease gene. The amplified products were sequenced by the dideoxy chain termination method. RESULTS The data revealed no disease-specific sequence alterations in the Norrie disease gene. CONCLUSION Although we cannot completely exclude the possibility of the Norrie disease gene as a candidate gene, the above results suggest that the structural and functional changes in the Norrie disease gene are not associated with clinically typical retinoschisis families that do not contain mutations in the coding regions and splice sites of the retinoschisis gene.

Evaluation of RP2 and RP3 genes in an X-linked RP family manifesting loss of central vision and preserved peripheral function

AbstractX-Linked retinitis pigmentosa is a most severe and heterogeneous disorder of the retina. Recently, genes (RP2 and RPGR) from two X-linked loci have been positionally cloned and mutations have been identified in many families. To further evaluate allelic and non-allelic heterogeneity and the genotype — phenotype relationships, and to determine the prevalence of mutations in the gene, we have analyzed one previously unreported X-linked retinitis pigmentosa family, using a combination of haplotype analysis and DNA sequencing. Our extensive analysis of the RP2 gene failed to detect any disease — causing or polymorphic mutations. In the case of the RP3 gene, the alleles of the dinucleotide repeat marker did not segregate with the disease. Although we cannot completely exclude the possibility of the RP2 and RP3 genes as candidate genes, the above results suggest that structural and functional changes associated with the RP2 gene are not responsible for the phenotype in the family analyzed. Further identification of the X-linked genes may facilitate the elucidation of the molecular basis of the disorder in the family analyzed.