Interestingly, a variant allele of PDCD1 804C>T has previously been associated with susceptibility for ankylosing spondylitis and type I diabetes.14 Possibly, this could be related to a decreased activity profile of the PD-1 pathway in patients harboring this SNP, and these patients may therefore experience less inhibition of T cell activation (Fig. 1). Here, PDCD1 is linked to ankylosing spondylitis.