Implications of HLA diversity among regions for bone marrow donor searches in Japan

Japan is an island country, and the Japanese people have had minimal genetic exchange with other ethnolinguistic groups. Consequently, the population is highly uniform and has limited HLA diversity relative to people from other countries. However, Japan has three ethnolinguistic groups, and HLA distributions differ depending on geographic region. To collect an HLA-rich variety of bone marrow bank donor registrants, it is essential to know the precise distribution of HLA in Japan. We analyzed HLA alleles and haplotypes based on HLA information of 177 041 bone marrow donor registrants. Registrants were grouped depending on the prefecture and region (a group of prefectures) as commonly used in Japan. The prefectures did not show the same distributions, but the tendency was similar for each region. We found that Okinawa Prefecture and the mainland can be clearly divided as haplotypes: [A*24:02-C*01:02-B*54:01-DRB1*04:05] and [A*24:02-C*01:02-B*59:01-DRB1*04:05] were typically found in Okinawa (P = .02, P < .001). Moreover, these types were found almost exclusively in Japan and Korea. Donor registration centers of the Japan Marrow Donor Program are currently located in all prefectures. It is essential to deploy registration centers to collect registrants with a large variety of HLA types covering all of Japan.