Genomewide Scan of Ocular Refraction in African-American Families Shows Significant Linkage to Chromosome 7p15

Refractive development is influenced by environmental and genetic factors. Genetic studies have identified several regions of linkage to ocular refraction, but none have been carried out in African-derived populations. We performed quantitative trait locus linkage analyses in AfricanAmerican (AA) families to identify genomic regions responsible for refraction. We recruited 493 AA individuals in 96 families to participate in the Myopia Family Study. Genotyping of 387 microsatellite markers was performed on 398 participants. The mean refraction among genotyped individuals was −2.87 D (SD = 3.58) and myopia of at least 1 D was present in 267 (68%) participants. Multipoint, regression-based, linkage analyses were carried out on a logarithmic transformation of ocular refraction using the statistical package MERLIN-REGRESS. Empirical significance levels were determined via 4,898 whole-genome gene-dropping simulations. Linkage analyses were repeated after clustering families into two subgroups based on admixture proportions as determined by the software package STRUCTURE. Genomewide significant linkage was seen at 47 cM on chromosome 7 (logarithm of the odds ratio (LOD) = 5.87, P = 0.00005). In addition, three regions on chromosomes 2p, 3p and 10p showed suggestive evidence of linkage (LOD > 2, P < 0.005) for ocular refraction. We mapped the first quantitative trait locus for ocular refraction in an AA population to chr.7p15. Two previous studies in European-derived families reported some evidence of linkage to a nearby region, suggesting that this region may contain polymorphisms that mediate refraction across populations. The genomic region under our linkage peak spans ~17 Mb and contains ~170 genes. Further refinement of this region will be pursued in future studies.