Linkage of Myopia to PAX6 in an unselected twin sample

Abstract

Abstract: : Purpose: We have previously reported a strong genetic influence on refractive error (heritability 85%) in an unselected sample of 506 volunteer twin pairs. We demonstrated (ARVO 2003 Abstract 2015) significant linkage at four loci in a genome–wide screen of 221 dizygotic sib–pairs, with the maximum linkage peak (LOD 6.1) at chromosome 11p13. The PAX6 gene is fundamental to eye development, and has been the sole gene implicated in aniridia; mutations cause this congenital abnormality, which may show progressive changes in life. The location of PAX6 at 11p13 suggested this as a candidate gene responsible for the myopia linkage signal in this area. Methods: A search of available public databases of single nucleotide polymorphisms (SNPs) in and around the PAX6 gene identified 29 possible SNPs. Of these, 5 could not be set up, and the resulting 24 SNPs were examined in a subsample of 20 twins. 7 SNPs showed no polymorphisms, resulting in 17 SNPs (on average 1 per 2kB) examined. Haplotype Linkage Disequilibrium tagging was used to examine blocks of SNPs making up the same haplotype. These SNPs were then genotyped in 190 dizygotic twin pairs to test for linkage and association. Results: Haplotype tagging identified 5 SNPs (tSNPs), which explained 0.999 of the haplotype diversity arising from 17 common allele frequency SNPs. Analysis of the tSNP genotypes and haplotypes using QTDT showed strong evidence of linkage for all markers (minimum of chi–sq₁ = 64.8, p = 8e–16). No evidence of population stratification was observed. In tests of total phenotypic association to the markers, none of the individual SNPs showed any evidence of association, but an omnibus test of association for the haplotypes showed marginal evidence of association (chi–sq₄ = 9.97, p = 0.041). Combined tests of linkage and association did not significantly reduce the observed linkage signal. Conclusions: The quantitative trait of spherical equivalent shows strong evidence of linkage to PAX6 and weak haplotypic association, suggesting that genetic variant(s) are located in the vicinity of the gene, probably within regulatory or promoter regions of PAX6.

Keywords: myopia • refractive error development • genetics