Research report: Frequencies of mica gene polymorphism: a comparison between Indonesians on Bacan Island and suburban Japanese.

MHC class I chain related gene A (MICA) is located near the HLA-B gene on the short arm of human chromosome 6. In the transmembrane (TM) of region of MICA, there is a trinucleotide repeat (GCT/AGC) microsatellite polymorphism in exon 5. Five alleles with 4, 5, 6 and 9 repetitions or 5 repetitions with 1 additional nucleotide insertion (GGCT) are identified and they were named A4, A5, A5.1, A6, and A9 respectively. We report the allele frequencies of 127 Indonesians on Bacan Island and 250 Japanese in the Kanto area. From the genotyping result, the frequency among Indonesians was as follows: A4 15.4%, A5 26.0%, A5.1 16.5%, A6 5.5%, and A9 36.6%. The frequency among Japanese was as follows: A4 20.6%, A5 28.1%, A5.1 10.8%, A6 27.2%, and A9 13.2%. Allele 9 is significantly increased and allele 6 significantly decreased in Indonesians compared with Japanese subjects. The results suggested that MICA microsatellite polymorphism are quite different in each race. Among Indonesians, the frequency of MICA-A9 allele, which was reported to be negatively associated with Behçet's disease, was significantly higher, whereas the MICA-A6 allele frequency, which was reported to be positively associated with Behçet's disease, was significantly lower among Japanese.