Neil D. Ebenezer

A Human Homolog of Yeast Pre-mRNA Splicing Gene, PRP31, Underlies Autosomal Dominant Retinitis Pigmentosa on Chromosome 19q13.4 (RP11)

We report mutations in a gene (PRPF31) homologous to Saccharomyces cerevisiae pre-mRNA splicing gene PRP31 in families with autosomal dominant retinitis pigmentosa linked to chromosome 19q13.4 (RP11; MIM 600138). A positional cloning approach supported by bioinformatics identified PRPF31 comprising 14 exons and encoding a protein of 499 amino acids. The level of sequence identity to the yeast PRP31 gene indicates that PRPF31 is also likely to be involved in pre-mRNA splicing. Mutations that include missense substitutions, deletions, and insertions have been identified in four RP11-linked families and three sporadic RP cases. The identification of mutations in a pre-mRNA splicing gene implicates defects in the splicing process as a novel mechanism of photoreceptor degeneration.

Mutations in sodium-borate cotransporter SLC4A11 cause recessive congenital hereditary endothelial dystrophy (CHED2)

Congenital hereditary endothelial dystrophy (CHED) is a heritable, bilateral corneal dystrophy characterized by corneal opacification and nystagmus. We describe seven different mutations in the SLC4A11 gene in ten families with autosomal recessive CHED. Mutations in SLC4A11, which encodes a membrane-bound sodium-borate cotransporter, cause loss of function of the protein either by blocking its membrane targeting or nonsense-mediated decay.

Chromosomal duplication involving the forkhead transcription factor gene FOXC1 causes iris hypoplasia and glaucoma

The forkhead transcription factor gene FOXC1 (formerly FKHL7) is responsible for a number of glaucoma phenotypes in families in which the disease maps to 6p25, although mutations have not been found in all families in which the disease maps to this region. In a large pedigree with iris hypoplasia and glaucoma mapping to 6p25 (peak LOD score 6.20 [recombination fraction 0] at D6S967), no FOXC1 mutations were detected by direct sequencing. However, genotyping with microsatellite repeat markers suggested the presence of a chromosomal duplication that segregated with the disease phenotype. The duplication was confirmed in affected individuals by FISH with markers encompassing FOXC1. These results provide evidence of gene duplication causing developmental disease in humans, with increased gene dosage of either FOXC1 or other, as yet unknown genes within the duplicated segment being the probable mechanism responsible for the phenotype.

RPGR mutation associated with retinitis pigmentosa, impaired hearing, and sinorespiratory infections

Retinitis pigmentosa (RP) is a progressive retinal degeneration that affects about 1 in 4000 of the population.1 Approximately 15–30% of patients with RP have X linked retinitis pigmentosa (XLRP), which is the most severe form of RP consistently manifesting early in life.2,3 Night blindness is usually present in early childhood with loss of peripheral visual fields and ultimately central vision, resulting in registered blindness by the end of the third decade. Female carriers display a broad spectrum of fundus appearances ranging from normal to extensive retinal degeneration.4–6 XLRP is genetically heterogeneous with two major loci, RP2 (Xp11.23) and RP3 (Xp21.1). Both disease genes have now been identified (respectively RP2 7 and RPGR 8–10) with RP2 mutations causing disease in approximately 15% of XLRP families,11,12 while RPGR mutations are reportedly more common, accounting for up to 75% of XLRP.10 Two other rare loci for XLRP have also been described on Xp22 and Xq26–27.13,141 Hong et al 15 described the phenotype and pathology of an RPGR knockout mouse model. They showed the subcellular localisation of RPGR to the photoreceptor connecting cilia, and in the absence of RPGR partial mislocalisation of essential outer segment proteins. These data suggest a putative role for RPGR in the retina, controlling movement of essential proteins from the inner to the outer segment of photoreceptors via the connecting cilia. Several groups have recently identified a retina specific RPGR interacting protein (RPGRIP1).16–18 This protein also localises to the photoreceptor connecting cilium and is thought to be a structural component of the ciliary axoneme.18 Subsequent mutation screening in patients suffering from retinal diseases has identified mutations in RPGRIP1 as a cause of Leber congenital amaurosis.19,20 In this report, we present the phenotype of …

A major marker for normal tension glaucoma: Association with polymorphisms in the OPA1 gene

Abstract. Normal tension glaucoma (NTG) is a major form of glaucoma, associated with intraocular pressures that are within the statistically normal range of the population. OPA1, the gene responsible for autosomal dominant optic atrophy represents an excellent candidate gene for NTG, as the clinical phenotypes are similar and OPA1 is expressed in the retina and optic nerve. Eighty-three well-characterized NTG patients were screened for mutations in OPA1 by heteroduplex analysis and bi-directional sequencing. Sequences found to be altered in NTG subjects were examined for variations in 100 population controls. A second cohort of 80 NTG patients and 86 population controls was subsequently screened to determine whether the initial findings could be replicated. A single nucleotide polymorphism (SNP) on intervening sequence (IVS) 8 (IVS8 + 4 C/T) was found to be strongly associated with the occurrence of NTG in both cohorts (χ2=7.97, P=0.005 in the first cohort, χ2=9.93, P=0.002 in the second cohort; odds ratio 3.1 (95% CI: 1.8–5.6). A second SNP (IVS8 + 32 T/C) appeared to be associated with disease in the first cohort (χ2=4.71, P=0.030), but this finding could not be replicated in the second cohort. In the combined cohort, the compound at-risk genotype IVS8 + 4 C/T, + 32 T/C was strongly associated with the occurrence of NTG (χ2=22.04, P=0.00001 after correcting for testing four genotypes). These results indicate that polymorphisms in the OPA1 gene are associated with NTG and may be a marker for the disease.

Prevalence of optineurin sequence variants in adult primary open angle glaucoma: implications for diagnostic testing

Glaucoma, the leading cause of irreversible blindness world wide, affecting about 70 million people,1,2 is characterised by progressive loss of optic nerve axons and visual field damage. As the condition is insidious, the diagnosis is often missed and the disease detected only later when patients have severe and irreversible visual impairment. Adult primary open angle glaucoma (POAG) is a major form of glaucoma world wide. Most POAG in white and Afro-Caribbean populations is of the high tension glaucoma (HTG) type, with raised intraocular pressure (IOP) being a major contributory factor for visual loss.3–6 Normal tension glaucoma (NTG) is another important subtype of POAG in which typical glaucomatous cupping of the optic nerve head and visual field loss are present, but IOPs are consistently within the statistically normal population range. This accounts for about a third of all patients with POAG.4–7 Although the proportion of cases of glaucoma with a genetic basis has not been precisely defined, an increasing body of evidence derived from a range of populations indicates that glaucoma has a substantial heritable basis. It has been estimated that 20%–60% of patients with the disease have a family history, and under-reporting of a family history has been well documented in glaucoma.8–11 In 1997, myocilin ( MYOC , MIM 601652), located on chromosome 1q25,12 was the first POAG gene to be characterised and found to be mutated in patients with juvenile and adult onset POAG.13 Subsequent studies found that MYOC mutations account for fewer than 5% of cases of adult POAG,13–17 with lower frequencies of MYOC mutations in Chinese and Japanese populations compared to white populations.16,18 Rezaie et al 19 recently identified a second POAG gene, optineurin ( OPTN , MIM 602432) in the GLC1E interval on chromosome …

Investigating the association between OPA1 polymorphisms and glaucoma: comparison between normal tension and high tension primary open angle glaucoma

Abstract.OPA1, the gene responsible for autosomal dominant optic atrophy, represents a good candidate gene for glaucoma, as there are similarities in the clinical phenotype and OPA1 is expressed in the optic nerve. Single nucleotide polymorphisms on intervening sequence (IVS) 8 of the OPA1gene (genotype IVS8+4 C/T;+32T/C) were recently found to be strongly associated with normal tension glaucoma (NTG). In order to investigate whether this association exists in patients with high-tension glaucoma (HTG), 90 well-characterized HTG patients were examined for the presence of these OPA1 polymorphisms by PCR amplification followed by bi-directional sequencing. Five out of 90 HTG subjects (5.6%; 95% CI 1.8–12.5) were found to carry the OPA1 genotype IVS 8+4 C/T; +32 T/C, compared with 32/163 (19.6%; 95% CI 13.8–26.6) NTG subjects [χ2=9.2, P=0.002, OR 4.1 (95% CI 1.6–11.1)], and 7/186 (3.8%; 95% CI 1.5–7.6) control subjects [χ2=0.47, P=0.49, OR 1.5 (95% CI 0.5–4.9)]. These results indicate that unlike NTG, the OPA1 genotype IVS8+4 C/T,+32T/C is not significantly associated with high-tension primary open angle glaucoma, and suggest genetic heterogeneity between the conditions.

Familial Glaucoma Iridogoniodysplasia Maps to a 6p25 Region Implicated in Primary Congenital Glaucoma and Iridogoniodysgenesis Anomaly

Familial glaucoma iridogoniodysplasia (FGI) is a form of open-angle glaucoma in which developmental anomalies of the iris and irido-corneal angle are associated with a juvenile-onset glaucoma transmitted as an autosomal dominant trait. A single large family with this disorder was examined for genetic linkage to microsatellite markers. A peak LOD score of 11.63 at a recombination fraction of 0 was obtained with marker D6S967 mapping to chromosome 6p25. Haplotype analysis places the disease gene in a 6.4-cM interval between the markers D6S1713 and D6S1600. Two novel clinical appearances extend the phenotypic range and provide evidence of variable expressivity. The chromosome 6p25 region is now implicated in FGI, primary congenital glaucoma, and iridogoniodysgenesis anomaly. This may indicate the presence of a common causative gene or, alternatively, a cluster of genes involved in eye development/function.

Identification of the gene for Nance-Horan syndrome (NHS)

Background: The disease intervals for Nance-Horan syndrome (NHS [MIM 302350]) and X linked congenital cataract (CXN) overlap on Xp22. Objective: To identify the gene or genes responsible for these diseases. Methods: Families with NHS were ascertained. The refined locus for CXN was used to focus the search for candidate genes, which were screened by polymerase chain reaction and direct sequencing of potential exons and intron-exon splice sites. Genomic structures and homologies were determined using bioinformatics. Expression studies were undertaken using specific exonic primers to amplify human fetal cDNA and mouse RNA. Results: A novel gene NHS, with no known function, was identified as causative for NHS. Protein truncating mutations were detected in all three NHS pedigrees, but no mutation was identified in a CXN family, raising the possibility that NHS and CXN may not be allelic. The NHS gene forms a new gene family with a closely related novel gene NHS-Like1 (NHSL1). NHS and NHSL1 lie in paralogous duplicated chromosomal intervals on Xp22 and 6q24, and NHSL1 is more broadly expressed than NHS in human fetal tissues. Conclusions: This study reports the independent identification of the gene causative for Nance-Horan syndrome and extends the number of mutations identified.

Genetic analysis of 14 families with Schnyder crystalline corneal dystrophy reveals clues to UBIAD1 protein function

Schnyder crystalline corneal dystrophy (SCCD) is a rare autosomal dominant disease characterized by progressive corneal opacification resulting from abnormal deposition of cholesterol and phospholipids. Recently, six different mutations on the UBIAD1 gene on chromosome 1p36 were found to result in SCCD. The purpose of this article is to further characterize the mutation spectrum of SCCD and identify structural and functional consequences for UBIAD1 protein activity. DNA sequencing was performed on samples from 36 individuals from 14 SCCD families. One affected individual was African American and SCCD has not been previously reported in this ethnic group. We identified UBIAD1 mutations in all 14 families which had 30 affected and 6 unaffected individuals. Eight different UBIAD1 mutations, 5 novel (L121F, D118G, and S171P in exon 1, G186R and D236E in exon 2) were identified. In four families with DNA samples from both affected and unaffected individuals, the D118G, G186R, T175I, and G177R mutations cosegregated with SCCD. In combination with our previous report, we have identified the genetic mutation in UBIAD1 in 20 unrelated families with 10 (including 5 reported here), having the N102S mutation. The results suggest that N102S may be a mutation hot spot because the affected families were unrelated including Caucasian and Asian individuals. There was no genotype phenotype correlation except for the T175I mutation which demonstrated prominent diffuse corneal haze, typically without corneal crystals. Protein analysis revealed structural and functional implications of SCCD mutations which may affect UBIAD1 function, ligand binding and interaction with binding partners, like apo E.