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A peculiar case of recombination at HLA-A locus.

Recombination of human leukocyte antigen (HLA) antigens during meiosis can lead to difficulty in haplotype construction which is mandatory for work up of patients for bone marrow transplantation. We report on a patient who showed recombination at A locus of his paternal chromosome. HLA typing at low resolution was performed as per the protocol by Luminex-Reverse sequence specific oligonucleotide probes using (Genprobe Lifecodes, Stanford, CA) kits for family members of a 4-year-old child diagnosed to be having acute lymphoblastic leukemia. Haplotype construction was performed manually as results of patient, his parents and siblings were available. The patient’s sample was retyped by sequence specific primers using Innotrain (Gmbh, Ketsch, Germany) as his haplotype could not be explained by the codominant inheritance of HLA molecules which follow Mendelian laws of inheritance. The paternal and maternal haplotypes were (a, b) and (c, d), respectively, and are shown in Table 1. The patient turned out to be (b/a, d) and his sibling was (b, d). The incidence of meiotic recombination is approximately 1% (1). We have previously reported on two cases of recombination (2). It may occur simultaneously at more than one locus (3) and sometimes lead to formation of novel alleles (4). Recombination should be distinguished from loss of heterozygosity in which will show as an undetected antigen and this can be confirmed by typing a sample from buccal mucosa or even a peripheral blood sample when the peripheral blast count is low (4). This should be specially thought of when the results of haplotype construction are unexpected. There may be undetected recombinations at the antigens not typed during the work of patients which also highlights the importance of typing for C and DQB1 antigens, as many centers requisition only ABDR typing and this may lead to significant graft versus host disease. If complete HLA typing has not been carried out this may be done when unexpected GVHD occurs in an apparently fully matched BMT.