The role of SIX6 in primary open-angle glaucoma

Abstract

Purpose: To identify sequence variants within and near the SIX6 gene, to assess their association with primary open angle glaucoma (POAG), and to perform functional testing.

Methods: Meta-analysis of the NEIGHBOR and GLAUGEN datasets have identified a region on chromosome 14q23 that is significantly associated with POAG risk (top SNP rs10483727,p-value=3.9 X 10-11, OR= 1.32) as well as POAG quantitative endophenotypes involving optic nerve measurements. This locus contains the homeobox gene SIX6, which is known to play a role in ocular development. To identify potential causal variants, we sequenced the exons and flanking regions of the SIX6 locus in 262 POAG cases and 279 POAG controls. Variants identified are currently being functionally tested: morpholino antisense oligonucleotides for targeted knockdown have been injected into developing zebrafish embryos. Phenotypic rescue is underway with SIX6 mRNAs containing variants identified inhuman patients.

Results: We identified six nonsynonymous changes in the SIX6 gene, including five novel variants (Glu93Gln, Glu129Lys, His141Asn (rs33912345), Leu205Arg, Thr212Met, and Ser242Ile). Using an allele-based chi-squared test, rs33912345 was significant associated with POAG (p-value=0.0005, OR=1.54). We replicated this association, using a logistic regression model adjusted for age and gender, in a larger case-control dataset consisting of 482 POAG cases and 433 POAG controls (p-value= 0.005, OR=1.40). We performed ordered subset analysis case-control (OSACC), a method for performing a series of stratified analyses, using an important quantitative POAG risk factor, intraocular pressure. Rs33912345 showed increased evidence of association (permutation p-value=0.00008, OR=1.71) in a subset of 206 cases with elevated intraocular pressure (>27mm hg). Rs33912345 also displays strong association with POAG risk after imputation of genotypes in the NEIGHBOR/GLAUGEN dataset of 3166 cases and 3391 controls (p-value= 4.2 x 10-10). Preliminary results of SIX6 knockdown in the zebrafish show reduced eye size.

Conclusions: The SIX6 gene contains multiple variants highly associated with POAG status. Both common and rare variants may confer disease risk for POAG.

Keywords: 539 genetics • 413 aging • 698 retinal development