HLA-B27 SUBTYPES IN ASIAN PATIENTS WITH ANKYLOSING-SPONDYLITIS

The aim of this study was to investigate the contribution of the diffe rent B27 subtypes to ankylosing spondylitis (AS) susceptibility The po lymerase chain reaction (PCR) in combination with the sequence-specifi c oligonucloetide probes (SSOs) was used to analyse the polymorphism i n exon 2 and 3 of HLA-B27 in two Asian groups with different genetic H LA structures: Indian (I) and Thai (T) populations. The same number of AS patients (45) and healthy B27 positive donors (n = 17) from both p opulations were analysed in order to ascertain the B27 subtypes. Three different findings can be concluded from this study: 1) B2707 has be en found to be associated with AS in both populations. This associatio n has not been previously reported in either ethnic group. 2) B2704 i s strongly associated with AS in the Thai patients (91% in AS vs. 47% in C; RR = 11.5; EF = 0.83). In contrast, B2704 was found with simila r frequency in Asian Indians AS patients and controls (41% in AS vs. 4 1% in C.). 3) B2706 was found overrepresented in control populations and absent in AS patients (0% in AS vs. 47% in C.; p(c) < 10(-6)) show ing the maximum value of protective fraction (PF = 1). The B2706 nega tive association with AS has not been previously described in other et hnic groups and could indicate a protective effect of this subtype on AS susceptibility. The B2706 allele has two changes relative to B*270 4 at residue 114 (His to Asp) and 116 (Asp to Tyr) in the pockets DIE. The importance that these differences can play in the pathogenesis of AS are discussed.