Association of MICA alleles and HLA-B51 in Italian patients with Behçet's disease.

OBJECTIVE: To evaluate the distribution of the MHC class I chain related gene A transmembrane (MICA-TM) alleles in Italian patients with Behçet's disease (BD), and to investigate the relative contribution of MICA alleles and HLA-B51 in the susceptibility and specific clinical features of BD. METHODS: A total of 69 consecutive Italian patients who satisfied the International Study Group criteria for BD were followed at rheumatology, ophthalmology, and neurology units during a 3 year period (1997-99). We selected 130 healthy subjects from the same geographic areas as controls. All patients and controls were examined for MICA microsatellite polymorphisms using polymerase chain reaction. Serological HLA class B51 typing was performed by a standard microlymphocytotoxicity technique. RESULTS: A strong association with HLA-B51 was observed in patients with BD (OR 5.7, 95% CI 2.8-11.3). The MICA-TM allele A6, in linkage disequilibrium with HLA-B51, was only slightly increased in patients compared to controls (60.9% vs 50.8%; p = NS). No significant associations between HLA-B51 or MICA-TM alleles and clinical subgroups, particularly central nervous system or eye involvement, were found. CONCLUSION: HLA-B51 is the most important susceptibility gene in BD. Association with MICA-A6, when it exists, is secondary to the strong linkage disequilibrium with HLA-B51.