An HLA-B null allele (B*1526N) with a stop codon in exon 3 generated by a point mutation

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Abstract
An HLA‐B null allele was identified in a Japanese family during histocompatibility testing for bone marrow transplantation. The propositus was a healthy Japanese woman with three children, and her parents were cousins. Serological HLA typing of the family members indicated that the propositus was homozygous for the A24‐Cw4‐B blank (B null)‐DR4.2‐DQ3 haplotype. Total RNA was extracted from peripheral blood of the propositus was converted to first‐strand cDNA using reverse transcriptase. The cDNA was amplified by the polymerasee chain reaction (PCR) using HLA‐B locus‐specific primers. The PCR product showed no change in size upon polyacrylamide gel electrophoresis (PAGE) compared to that of normal controls, suggesting that HLA‐B gene mRNA was normally expressed. The nucleotide sequence of the cDNA was the same as that of B*1501 except at nucleotide 369 or codon 123, where C was replaced with A; TAC encodes Tyr whereas TAA is a stop codon. This point mutation may have truncated the HLA‐B molecule of the propositus, resulting in the negative results we obtained with anti‐HLA‐B sera.