One of the interesting findings from the first series of results of GWAS is that several genes, and often the same SNPs, are associated with multiple traits. Some make immediate, intuitive sense, such as the associations of the SNP rs1051730 in CHRNA3 with both lung cancer [132] and nicotine dependence [133], while others are less obvious. For example rs10484554 in HLA-C was found associated with AIDS nonprogression [134] and susceptibility to early onset psoriasis [135]. The SNP rs2476601 in PTPN22 was found associated with Crohn’s disease [30], rheumatoid arthritis [136], and type 1 diabetes [4,32]. LDL cholesterol, triglycerides, and Alzheimer’s disease are another set of traits that were found associated with rs4420638 in APOE in independent studies [101,137,138]. These associations suggest a pleiotropic effect of the genes involved that may affect many different traits. An alternative explanation is that the different phenotypes associated with the same gene may be the endpoints of disease progression sharing a common mechanism that is regulated by the gene. For example, we observed that several well known aging genes, including Klotho, were associated with vasoocclusive
