Ordered subsets linkage analysis and expression profiling of chromosome 16p in age–related macular degeneration

Abstract

Abstract: : Purpose: In an effort to identify susceptibility genes for AMD, several genome–wide linkage screens have recently been completed. One of the consistent regions of interest across studies is chromosome 16p, which we have explored in more detail. Methods: The incorporation of disease–associated covariates into linkage analysis may help reduce genetic heterogeneity and thus increase statistical power to detect linkage. Ordered subsets analysis rank–orders family lod scores with respect to continuous covariates of interest to assess subgroup–specific evidence of linkage. Using 62 multiplex families genotyped for 389 microsatellite markers across the human genome, we incorporated the following covariate information on AMD patients into our linkage analysis: body mass index (BMI), blood pressure, and intraocular pressure (IOP). Results: We obtained a nonparametric multipoint lod score of 3.61 at marker D16S403 (23 Mb) in a subset of 9 families with average BMI of affected relatives ≥ 28.6, and a lod score of 3.85 near the same marker in a subset of 31 families with average IOP ≥ 15.0. Both lod score increases were statistically significant by permutation testing (p=0.04; p=0.03, respectively). To follow–up these intriguing findings, we have genotyped 25 SNPs at approximately 1 Mb density in a 20 Mb region centered on D16S403 in a larger data set of 115 multiplex families. Singleton families, unrelated AMD patients and rigorously examined controls were genotyped as well (920 samples total). Preliminary analyses continue to support linkage to a similar map position in a subset of families characterized by a higher cardiovascular risk profile (lod score 3.43). Family–based analysis gave evidence for significant association (p=0.002) with an SNP 7 Mb proximal to D16S403. Conclusions: We continue to see a strong linkage signal on chromosome 16p in families with cardiovascular risk factors and predominantly neovascular AMD. Additional genotyping and macular expression profiling of our 20 Mb region of interest for further localization of a putative AMD susceptibility gene is underway.

Keywords: age–related macular degeneration • gene mapping • candidate gene analysis