Microsatellite polymorphisms of the MICA gene among Japanese patients with Behçet's disease.

BACKGROUND: Behçet's disease (BD) is a multisystemic inflammatory disease of unknown origin. Because some researchers have recently suggested a primary association of BD with the A6 allele of the human major histocompatibility complex class I chain-related A (MICA) gene, we investigated microsatellite polymorphisms of the MICA gene in subjects with and without BD.

METHODS: This was a case-control study of 23 Japanese patients with BD and 23 Japanese volunteers without BD who were compared for MICA microsatellite polymorphisms using the polymerase chain reaction (PCR). We also analysed associations between 5 MICA alleles and the clinical features of patients.

RESULTS: There was no significant difference between case patients and control subjects in phenotype frequencies. The MICA-A6 allele showed the strongest positive correlation with the human leukocyte antigen allele HLA-B51. Allele A5 showed a strong positive correlation with age at onset and a strong negative correlation with iridocyclitis and HLA-B51. A4 showed a strong negative correlation with ocular lesions and HLA-B51. Patients with the MICA-A6 allele had significantly higher HLA positivity than patients without the allele.

INTERPRETATION: While the MICA-A6 allele had no significant association with BD, it showed a strong association with HLA-B51. This finding suggests that an association between MICA-A6 and BD may be a secondary phenomenon related to HLA-B51. As several associations with MICA alleles and clinical features have been found, further investigation is expected to elucidate the biological mechanism of action of the MICA protein relative to disease onset.