Background
Over 160 disease phenotypes have been mapped to the major histocompatibility complex (MHC) region on chromosome 6 by genome-wide association study (GWAS), suggesting that the MHC region as a whole may be involved in the etiology of many phenotypes, including unstudied diseases. The phenome-wide association study (PheWAS), a powerful and complementary approach to GWAS, has demonstrated its ability to discover and rediscover genetic associations. The objective of this study is to comprehensively investigate the MHC region by PheWAS to identify new phenotypes mapped to this genetically important region.
Methods
In the current study, we systematically explored the MHC region using PheWAS to associate 2692 MHC-linked variants (minor allele frequency ≥ 0.01) with 6221 phenotypes in a cohort of 7481 subjects from the Marshfield Clinic Personalized Medicine Research Project.
Results
Findings showed that expected associations previously identified by GWAS could be identified by PheWAS (e.g. psoriasis, ankylosing spondylitis, type I diabetes, and celiac disease) with some having strong cross-phenotype associations potentially driven by pleiotropic effects. Importantly, novel associations with 8 diseases not previously assessed by GWAS (e.g., lichen planus) were also identified and replicated in an independent population. Many of these associated diseases appear to be immune-related disorders. Further assessment of these diseases in 16,484 Marshfield Clinic twins suggests that some of these diseases, including lichen planus, may have genetic etiologies.
Conclusions
These results demonstrate that the PheWAS approach is a powerful and novel method to discover SNP-disease associations, and is ideal when characterizing cross-phenotype associations, and further emphasizes the importance of the MHC region in human health and disease.