HLA-A*9, a probable secondary susceptibility marker to ankylosing spondylitis in Basque patients

HLA-B27 is strongly associated to ankylosing spondylitis (AS). The objectiv e of our study was to analyze HLA-B27 association, B27 subtype distribution and frequency oi other HLA class I and DR antigens in a group of Basque AS patients. HLA class I antigens were typed serologically and HLA-B27 and A9 subtypes were determined by DNA typing in samples from 46 patients with AS , 54 B27-positive spondyloarthropathies, 82 healthy Subjects and 20 B27-pos itive controls. A class I HLA 9.2 kb PvuII restriction fragment length poly morphism (RFLP), previously associated with AS, was analyzed in a represent ative group of patients and controls. We found that HLA-B*2705 conferred a relative risk oi 126 for AS in this group. HLA-AS (A*2402) allele was signi ficantly increased in AS patients compared with healthy controls and B27-po sitive control group (P-corr<0.0001) and also increased in patients affecte d with peripheral arthritis. No association between class I HLA 9.2 Iib RFL P and AS was found. These results suggest that HLA-A*9 allele itself or ano ther linked gene could act as a secondary acid independent susceptibility a llele to AS.