The ubiquity of pleiotropy in human disease

Pleiotropy has long been thought to be a common phenomenon in the human genome; however, until recently appropriate data was unavailable to test this hypothesis. Prior studies focused on assessing the prevalence of pleiotropy in only small subsets of phenotypes (≤ 53 phenotypes), without a truly comprehensive assessment of pleiotropy in the human genome. In this study, we determined the prevalence of pleiotropy, using the entire GWAS catalog (1094 disease phenotypes, 14,459 genes), as well as investigate the relationship between the degree of pleiotropy and the average effect size for each associating gene. The number of associating phenotypes per gene ranged from 1 to 53, with 44% of genes reported in the GWAS catalog associating with more than one phenotype. The proportion of genes shown to be pleiotropic has continued to increase as more studies are added to the catalog. We also found the degree of pleiotropy scales positively with a gene's average effect size (r = 0.04, p value = 0.0003) and negatively with the variance of effect sizes in genes with a given number of associating phenotypes (r = - 0.590, p value = 0.0019). Based on this and prior work, it is becoming evident that pleiotropy is a common, if not ubiquitous, phenomenon. These results have implications in understanding disease etiologies, potentially common biology underlying even disparate diseases, and in elucidating the genotype-phenotype map.