Eranga N. Vithana

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.

Polypoidal choroidal vasculopathy and neovascular age-related macular degeneration: Same or different disease?

Neovascular age-related macular degeneration (nAMD) is the commonest cause of severe visual impairment in older adults in Caucasian white populations. Polypoidal choroidal vasculopathy (PCV) has been described as a separate clinical entity differing from nAMD and other macular diseases associated with subretinal neovascularization. It remains controversial as to whether or not PCV represents a sub-type of nAMD. This article summarizes the current literature on the clinical, pathophysiological and epidemiological features and treatment responses of PCV and compares this condition to nAMD. Patients with PCV are younger and more likely Asians, and eyes with PCV lack drusen, often present with serosanguinous maculopathy or hemorrhagic pigment epithelial detachment, and have differing responses to photodynamic therapy and anti-vascular endothelial growth factor (VEGF) agents. There are also significant differences in angiographic and optical coherence tomography features between PCV and nAMD. Histopathological studies suggest differences in the anatomical details of the associated vascular abnormalities in the retina and choroids and the relative role of VEGF. There is emerging evidence of common molecular genetic determinants involving complement pathway and common environmental risk factors (e.g. smoking). Such information could further assist clinicians involved in the care of elderly patients with these conditions.

Alpha-B crystallin gene (CRYAB) mutation causes dominant congenital posterior polar cataract in humans.

Congenital cataracts are an important cause of bilateral visual impairment in infants. In a four-generation family of English descent, we mapped dominant congenital posterior polar cataract to chromosome 11q22-q22.3. The maximum LOD score, 3.92 at recombination fraction 0, was obtained for marker D11S898, near the gene that encodes crystallin alpha-B protein (CRYAB). By sequencing the coding regions of CRYAB, we found in exon 3 a deletion mutation, 450delA, that is associated with cataract in this family. The mutation resulted in a frameshift in codon 150 and produced an aberrant protein consisting of 184 residues. This is the first report of a mutation, in this gene, resulting in isolated congenital cataract.

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.

Genome-wide association analyses identify multiple loci associated with central corneal thickness and keratoconus

Central corneal thickness (CCT) is associated with eye conditions including keratoconus and glaucoma. We performed a meta-analysis on >20,000 individuals in European and Asian populations that identified 16 new loci associated with CCT at genome-wide significance (P < 5 × 10−8). We further showed that 2 CCT-associated loci, FOXO1 and FNDC3B, conferred relatively large risks for keratoconus in 2 cohorts with 874 cases and 6,085 controls (rs2721051 near FOXO1 had odds ratio (OR) = 1.62, 95% confidence interval (CI) = 1.4–1.88, P = 2.7 × 10−10, and rs4894535 in FNDC3B had OR = 1.47, 95% CI = 1.29–1.68, P = 4.9 × 10−9). FNDC3B was also associated with primary open-angle glaucoma (P = 5.6 × 10−4; tested in 3 cohorts with 2,979 cases and 7,399 controls). Further analyses implicate the collagen and extracellular matrix pathways in the regulation of CCT.

Collagen-related genes influence the glaucoma risk factor, central corneal thickness

Central corneal thickness (CCT) is a risk factor of glaucoma, the most common cause of irreversible blindness worldwide. The identification of genetic determinants affecting CCT in the normal population will provide insights into the mechanisms underlying the association between CCT and glaucoma, as well as the pathogenesis of glaucoma itself. We conducted two genome-wide association studies for CCT in 5080 individuals drawn from two ethnic populations in Singapore (2538 Indian and 2542 Malays) and identified novel genetic loci significantly associated with CCT (COL8A2 rs96067, p(meta) = 5.40 × 10⁻¹³, interval of RXRA-COL5A1 rs1536478, p(meta) = 3.05 × 10⁻⁹). We confirmed the involvement of a previously reported gene for CCT and brittle cornea syndrome (ZNF469) [rs9938149 (p(meta) = 1.63 × 10⁻¹⁶) and rs12447690 (p(meta) = 1.92 × 10⁻¹⁴)]. Evidence of association exceeding the formal threshold for genome-wide significance was observed at rs7044529, an SNP located within COL5A1 when data from this study (n = 5080, P = 0.0012) were considered together with all published data (reflecting an additional 7349 individuals, p(Fisher) = 1.5 × 10⁻⁹). These findings implicate the involvement of collagen genes influencing CCT and thus, possibly the pathogenesis of glaucoma.

Genome-wide association analyses identify three new susceptibility loci for primary angle closure glaucoma

Primary angle closure glaucoma (PACG) is a major cause of blindness worldwide. We conducted a genome-wide association study including 1,854 PACG cases and 9,608 controls across 5 sample collections in Asia. Replication experiments were conducted in 1,917 PACG cases and 8,943 controls collected from a further 6 sample collections. We report significant associations at three new loci: rs11024102 in PLEKHA7 (per-allele odds ratio (OR) = 1.22; P = 5.33 × 10−12), rs3753841 in COL11A1 (per-allele OR = 1.20; P = 9.22 × 10−10) and rs1015213 located between PCMTD1 and ST18 on chromosome 8q (per-allele OR = 1.50; P = 3.29 × 10−9). Our findings, accumulated across these independent worldwide collections, suggest possible mechanisms explaining the pathogenesis of PACG.

Association Analysis of CFH, C2, BF, and HTRA1 Gene Polymorphisms in Chinese Patients with Polypoidal Choroidal Vasculopathy

PURPOSE Polypoidal choroidal vasculopathy (PCV) is a major cause of serosanguinous maculopathy in Chinese patients with age-related macular degeneration (AMD). Variants in the CFH and HTRA1/LOC387715 genes are strongly associated with AMD in Caucasians and Chinese. Variants in the C2 and BF genes have been found to confer a significantly reduced risk of AMD. This study was undertaken to determine whether these associations occur in Chinese patients with PCV. METHODS Patients of Chinese ethnicity with clinically and angiographically diagnosed PCV and normal control subjects were recruited from the Singapore National Eye Centre. Five single-nucleotide polymorphisms (SNPs) in the CFH gene, two each within the C2 and BF genes and two variants located in the LOC387715 and HTRA1 genes, were screened in all patients and control subjects. RESULTS Seventy-two patients with PCV and 93 normal control subjects were studied. A significant association was noted with CFH variants rs3753394 and rs800292 among the PCV cases (P = 0.0015 and P = 0.0045, respectively). Individuals homozygous for the TT genotype of rs3753394 had a significantly higher risk (P = 0.0076) of PCV (OR = 4.29; 95% CI: 1.47-12.50) than those carrying a single copy of the T allele (P = 0.3210; OR = 1.69; 95% CI: 0.60-4.78), after adjustment for such risk factors as age and sex. The genotype frequencies of rs11200638 and rs10490924 in HTRA1 and LOC387715, respectively, were also found to be significantly different between patients with PCV and normal control subjects (P = 0.00032 and P = 0.003, respectively). The AA genotype of rs11200638 and TT genotype of rs10490924 conferred a 4.9-fold (95% CI: 1.85-12.95) and 4.89-fold (95% CI: 1.85-12.90) increased risk of PCV, respectively, after adjustment for age and sex. The Y402H variant of CFH (rs1061170) and the BF and C2 variants were not significantly different in patients and normal control subjects. CONCLUSIONS The SNPs rs3753394 and rs800292 of CFH and rs11200638 of HTRA1 are significantly associated with the risk of PCV in Chinese patients.

Genome-wide analysis of multi-ancestry cohorts identifies new loci influencing intraocular pressure and susceptibility to glaucoma

Elevated intraocular pressure (IOP) is an important risk factor in developing glaucoma, and variability in IOP might herald glaucomatous development or progression. We report the results of a genome-wide association study meta-analysis of 18 population cohorts from the International Glaucoma Genetics Consortium (IGGC), comprising 35,296 multi-ancestry participants for IOP. We confirm genetic association of known loci for IOP and primary open-angle glaucoma (POAG) and identify four new IOP-associated loci located on chromosome 3q25.31 within the FNDC3B gene (P = 4.19 × 10−8 for rs6445055), two on chromosome 9 (P = 2.80 × 10−11 for rs2472493 near ABCA1 and P = 6.39 × 10−11 for rs8176693 within ABO) and one on chromosome 11p11.2 (best P = 1.04 × 10−11 for rs747782). Separate meta-analyses of 4 independent POAG cohorts, totaling 4,284 cases and 95,560 controls, showed that 3 of these loci for IOP were also associated with POAG.

Missense mutations in the sodium borate cotransporter SLC4A11 cause late-onset Fuchs corneal dystrophya

Homozygous mutations in the Borate Cotransporter SLC4A11 cause two early‐onset corneal dystrophies: congenital hereditary endothelial dystrophy (CHED) and Harboyan syndrome. More recently, four sporadic patients with late‐onset Fuchs corneal dystrophy (FCD), a common age‐related disorder, were also reported to harbor heterozygous mutations at this locus. We therefore tested the hypothesis that SLC4A11 contributes to FCD and asked whether mutations in SLC4A11 are responsible for familial cases of late‐onset FCD. We sequenced SLC4A11 in 192 sporadic and small nuclear late‐onset FCD families and found seven heterozygous missense novel variations that were absent from ethnically matched controls. Familial data available for one of these mutations showed segregation under a dominant model in a three‐generational family. In silico analyses suggested that most of these substitutions are intolerant, whereas biochemical studies of the mutant protein indicated that these alleles impact the localization and/or posttranslational modification of the protein. These results suggest that heterozygous mutations in SLC4A11 are modest contributors to the pathogenesis of adult FCD, suggesting a causality continuum between FCD and CHED. Taken together with a recent model between FCD and yet another early onset corneal dystrophy, PPCD, our data suggest a shared pathomechanism and genetic overlap across several corneal dystrophies. Hum Mutat 31:1–8, 2010.