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ALLELE LEVEL TYPING OF HLA-B LOCUS BY MULTIPLEXED SINGLE NUCLEOTIDE EXTENSION (MSNE) AND A STUDY OF B15 IN DIFFERENT ETHNIC GROUPS.
M. Han, PhD, Y. Tan, MD, Y. Guo, MD, A. Romphruk, M.Sc., C. Leelayuwat, PhD and P. Stastny, MD. Dallas TX, UT Southwestern Med Cntr, Internal Medicine and Thailand Khon Kaen Univ.

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Typing of HLA-B by the MSNE method was developed to determine HLA-B locus alleles. Exons 2 and 3 of the HLA-B genes were amplified with 15 pairs of group-specific primers and analyzed by MSNE as previously reported for HLA-A, for high resolution typing. Over 300 samples were typed, and the results were in concordance with previous typing by SBT or SSOP. Ambiguities were rarely observed when both alleles of certain individuals fell into same HLA-B group. HLA-B*15 is the most polymorphic family of class I genes in the HLA system. It is known to be common in Thailand, however comprehensive high resolution typing has never been performed in this population. In the present study we performed allele-level typing of 196 B*15-positive individuals. They included 69 Thais, 83 Caucasians, 26 African-Americans, and 18 Hispanics. Overall 9 different alleles were detected in Thai, 5 in Caucasians, 6 in African-Americans and 5 in Hispanics. In Thai, B*1502 was the most frequent allele with a gene frequency of 0.275, followed by B*1525 (0.073), B*1535 (0.044) and B*1501 (0.044). B*1502, B*1525 and B*1535 were only seen in this population. The predominant alleles found in other races were B*1501 in Caucasians (0.434), B*1503 in African-Americans (0.212), and B*1501 in Hispanics (0.194). B*1502 has been reported to be a predictor of carbamazepine-induced Stevens-Johnson syndrome (CBZ-SJS), thus the high frequency of B*1502 in Thai may suggest a correlation with the high incidence of CBZ-SJS in that population. In conclusion, the MSNE typing method clearly and easily resolved all of the B-locus alleles tested. It is our choice for high resolution typing in a clinical setting.