Exome-wide study of ankylosing spondylitis demonstrates additional shared genetic background with inflammatory bowel disease

Ankylosing spondylitis (AS) is a common chronic immune-mediated arthropathy affecting primarily the spine and pelvis. The condition is strongly associated with HLA-B*27 as well as other human leukocyte antigen variants and at least 47 individual non-MHC-associated variants. However, substantial additional heritability remains as yet unexplained. To identify further genetic variants associated with the disease, we undertook an association study of AS in 5,040 patients and 21,133 healthy controls using the Illumina Exomechip microarray. A novel association achieving genome-wide significance was noted at CDKAL1. Suggestive associations were demonstrated with common variants in FAM118A, C7orf72 and FAM114A1 and with a low-frequency variant in PNPLA1. Two of the variants have been previously associated with inflammatory bowel disease (IBD; CDKAL1 and C7orf72). These findings further increase the evidence for the marked similarity of genetic risk factors for IBD and AS, consistent with the two diseases having similar aetiopathogenesis.