ERAP-HLA associations have also been reported in Ankylosing spondylitis and Behcet's disease, suggesting shared pathogenic pathways among these diseases. The combined Birdshot risk polymorphisms at 5q15 linked to ERAP1 and ERAP2 genes (T-rs10044354-C-rs2287987) are only observed in HLA-A29-positive individuals in populations in which BU is “endemic”, explaining why BU is reported merely in populations of Western European Ancestry (Spain, France, The Netherlands, Great Britain, but also non-european countries such as Puerto Rico). [9] Functional analysis of patient-derived immune cells revealed that ERAP2 increases the abundance of peptides that specifically bind to HLA-A29 and further supports that the antigen presentation pathway drives the etiology of BSCR.