Large Scale Mutation/Polymorphism Analysis of WDR36, the Third Glaucoma–Causing Gene at GLC1G, in the French–Canadian Population of Québec

Abstract

Purpose: : WDR36 was recently characterized as the third primary open–angle glaucoma (POAG) gene mapped at the GLC1G locus on chromosome 5q22.1 (Hum Mol Gen (2005)14:725). We determined the prevalence of WDR36 variations in the French–Canadian population.

Methods: : All of the 23 coding exons and flanking introns of WDR36 were screened by direct genomic sequencing in 295 unrelated POAG patients with ocular hypertension and 31 normal tension glaucoma (NTG) subjects from the Province of Québec, Canada. For each exon, sequencing data was analyzed in a minimum of 284 patients. 107 asymptomatic subjects served as controls for all exons. Exons 1, 5 and 11 were screened in 64 additional controls.

Results: : Overall, 23 sequence alterations were detected. 18 of these encoded non–synonymous amino acid changes. The other 5 variations were highly polymorphic SNPs with no effect on the protein. Eleven (11) of the non–synonymous variants were carried each by only one of our patients; none of them were detected in any of the controls. Eight (8) of these 11 variants were novel. These were the T65K, D126N, K284T, I292T, N351T, H411R, N626T and G851R variants. The other 3 non–synonymous variants, observed once in the patients, were the N355S, R529Q and M671V variants. The most common non–synonymous variation in our population was the H212P variant, previously reported as the Y216P disease–susceptibility mutation and encoded by exon 5. This variant was detected in 13/291 (4.5%) glaucoma probands and 3/168 (1.8%) controls. The A449T variant, encoded by exon 11, was observed in 3/294 glaucoma probands and 1/162 controls. The L25P potential susceptibility mutation in exon 1 was observed in 12/307 POAG probands and 3/171 controls. Prevalence of the L25P, H212P and A449T variations showed no statistical differences between patients versus controls. The D658G alteration, described as a disease–causing mutation, was found in 3/311 patients and 3/107 controls. Further ascertainment of the glaucoma relatives of two POAG probands who carried a H212P or D658G variation did not show segregation of the respective variant with the disease phenotype in these kindreds.

Conclusions: : WDR36 is a highly polymorphic gene. In the French–Canadian population, prevalence of WDR36 variations was higher in glaucoma patients than in controls. Our study suggests that WDR36 variants may contribute to the glaucoma phenotype by interacting with other POAG genes and/or that WDR36 is acting as a modifier gene.

Keywords: genetics • gene screening • gene modifiers