The spectrum of retinal diseases caused by NR2E3 mutations in Israeli and Palestinian patients.

OBJECTIVES: To evaluate the involvement of NR2E3 in inherited retinal degenerative diseases in the Israeli and Palestinian populations and to study phenotypic variability in patients who are homozygous for the same mutation. METHODS: Patients from 35 families underwent clinical evaluation, including a full ophthalmologic examination and electroretinography. Genetic analyses included direct sequencing of polymerase chain reaction products and haplotype reconstruction. RESULTS: We recruited 6 consanguineous Muslim families and 2 Jewish families with enhanced S-cone syndrome. Patients from 4 of the Muslim families were homozygous for the same NR2E3 mutation, c.119-2A>C, but showed considerable variability in fundus appearance and retinal function, even among patients of comparable ages. Both Jewish patients were compound heterozygotes for the c.932G>A mutation in combination with c.194-202del9bp or a novel splice-site mutation, c.747+1G>C. Homozygosity analysis in 27 consanguineous families with retinitis pigmentosa revealed a homozygous mutation, c.932G>A, in 2 families. The electroretinographic responses in these patients were compatible with retinitis pigmentosa and did not show the characteristic enhanced S-cone syndrome pattern. CONCLUSION: Our results demonstrate the involvement of NR2E3 in enhanced S-cone syndrome and retinitis pigmentosa phenotypes in our populations. CLINICAL RELEVANCE: Patients with NR2E3 mutations may manifest variable phenotypes. Moreover, patients who are homozygous for the same NR2E3 mutation have variable expression of retinal disease, suggesting the involvement of modifier genes.

Four USH2A founder mutations underlie the majority of Usher syndrome type 2 cases among non-Ashkenazi Jews.

Type 2 Usher syndrome (USH2) is a recessively inherited disorder, characterized by the combination of early onset, moderate-to-severe, sensorineural hearing loss, and vision impairment due to retinitis pigmentosa. From 74% to 90% of USH2 cases are caused by mutations of the USH2A gene. USH2A is composed of 72 exons, encoding for usherin, an extracellular matrix protein, which plays an important role in the development and maintenance of neurosensory cells in both retina and cochlea. To date, over 70 pathogenic mutations of USH2A have been reported in individuals of various ethnicities. Many of these mutations are rare private mutations segregating in single families. The aim of the current work was to investigate the genetic basis for USH2 among Jews of various origins. We found that four USH2A mutations (c.239-240insGTAC, c.1000C>T, c.2209C>T, and c.12067-2A>G) account for 64% of mutant alleles underlying USH2 in Jewish families of non-Ashkenazi descent. Considering the very large size of the USH2A gene and the high number of mutations detected in USH2 patients worldwide, our findings have significant implications for genetic counseling and carrier screening in various Jewish populations.

A novel de novo PAX6 mutation in an Ashkenazi-Jewish family with aniridia.

PURPOSE: To report a novel de novo PAX6 mutation in an Ashkenazi-Jewish family with autosomal dominant aniridia. METHODS: A mother and her daughter of Ashkenazi-Jewish origin were diagnosed with aniridia. Blood samples were drawn from family members and DNA was analyzed by direct sequencing and microsatellite marker analysis. RESULTS: The index patient and her daughter were affected with aniridia accompanied by congenital cataract, nystagmus, and glaucoma. A heterozygous PAX6 frameshift mutation in exon 6 (c.577_578insG, insG@Gly72) was identified in the affected individuals and not in any of the unaffected family members including the parents of the index patient. Microsatellite analysis revealed that the index patient inherited the disease haplotype from her unaffected father. A sequence analysis of human PAX6 expressed sequence tags revealed the identification of spliced transcripts initiating from introns 4, 6, 7, 8, and 11. CONCLUSIONS: A novel de novo frameshift mutation in PAX6, which presumably occurred in the paternal gamete, was found in a family with autosomal dominant aniridia. The location of the mutation suggests that only full-length PAX6 isoforms would be disrupted, indicating that the normal expression of shorter, paired-less, protein isoforms cannot prevent manifestation of the disease.

Microarray-based gene expression analysis during retinal maturation of albino rats.

BACKGROUND: In recent years, the rat has become a commonly-used animal model for the study of retinal diseases. Similar to other tissues, the retina undergoes significant functional changes during maturation. Aiming to gain knowledge on additional aspects of retinal maturation, we performed gene expression and histological analyses of the rat retina during maturation. METHODS: Rat retinas were dissected at three time points. Histological examination of the samples was performed, and the expression levels of retinal genes were evaluated using the rat whole-genome microarray system. Quantitative real-time PCR analysis was used to validate selected expression patterns. Various statistical and bioinformatic tools were used to identify differentially expressed genes. RESULTS: The microarray analysis revealed a relatively high number of highly expressed non-annotated genes. We identified 603 differentially expressed genes, which were grouped into six clusters based on changes in expression levels during the first 20 weeks of life. A bioinformatic analysis of these clusters revealed sets of genes encoding proteins with functions that are likely to be relevant to retinal maturation (potassium, sodium, calcium, and chloride channels, synaptic vesicle transport, and axonogenesis). The histological analysis revealed a significant reduction of outer nuclear layer thickness and retinal ganglion cell number during maturation. CONCLUSIONS: These data, taken together with our previously reported electrophysiological data, contribute to our understanding of the retinal maturation processes of this widely-used animal model.

A complex expression pattern of Pax6 in the pigeon retina.

PURPOSE: The retina of some avian species contains two macular regions, making it an excellent model for retinal, and especially macular, development. Previous studies have provided evidence of the involvement of Pax6 in macular development. The purpose was to perform a comprehensive expression analysis of Pax6 isoforms in different regions of the pigeon retina. METHODS: The different mRNA transcripts were amplified by RT-PCR and characterized by sequencing analysis. Semiquantitative PCR and quantitative real-time PCR analyses were used to study the level of expression of each transcript. Western blot analysis was performed on both the cytosolic and nuclear cell fractions. RESULTS: An evolutionary analysis of all human-chicken retinal homologues revealed that Pax6 is one of the most conserved retinal genes. By alternative splicing and alternative initiation of transcription, Pax6 produces 41 different mRNA transcripts, encoding 17 protein isoforms in the pigeon retina, five of which are paired-less cytosolic proteins. Semiquantitative expression analysis revealed that the short, paired-less, transcripts have a relatively high level of expression. Quantitative real-time PCR analysis of the central macula, red area, and peripheral retina revealed a spatial and temporal expression profile indicating that many Pax6 transcripts take a part in macular development. CONCLUSIONS: These data suggest that Pax6, a highly conserved gene, can maintain evolutionarily conserved variability at the protein level by alternative splicing and initiation mechanisms, allowing it to perform multiple functions. The variability in the length of the paired domain suggests that the different Pax6 isoforms activate different sets of genes.