Association of major histocompatibility complex class I chain-related gene A and HLA-B alleles with Behcet's disease in Turkey

Purpose: Behcet'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 (c) Japanese Ophthalmological Society 2007.