Association of Major Histocompatibility Complex Class I Chain-Related Gene A and HLA-B Alleles with Behçet's Disease in Turkey

Abstract

Purpose Behçet's disease (BD) is known to be associated with HLA-B *51 in many different ethnic groups. Recently, the major histocompatibility complex class I chain-related gene A ( MICA ), located near the HLA-B gene, has been proposed as a candidate gene for BD susceptibility in several ethnic groups. To compare the relative contribution of MICA polymorphisms and HLA-B *51 to BD in different ethnic groups, we studied MICA polymorphisms in Turkish BD patients. Methods Thirty-three Turkish BD patients and 65 healthy controls were enrolled for analysis of polymorphisms in the extracellular domains of MICA . Results The phenotype frequencies of MICA *009 were significantly higher in BD patients (75.8%) than in controls (29.2%) ( P = 0.000015). HLA-B *51 was also significantly more frequent in BD patients (81.8%) than in controls (29.2%) ( P = 0.0000007). A strong association existed between MICA *009 and HLA-B *51. To assess the confounding effect of MICA *009 on HLA-B *51, we performed a stratification analysis that showed that BD was distinctly associated only with HLA-B *51. Conclusion Our results indicate that the major susceptibility gene for BD is HLA-B *51 and that the association between MICA *009 and BD arises from a strong linkage disequilibrium with HLA-B *51. However, we suggest that MICA *009 likely elicits an immune effect secondary to BD. Jpn J Ophthalmol 2007;51:431–436 © Japanese Ophthalmological Society 2007