Serologic and molecular studies of two kindreds expressing recombinant HLA DR1/DR2 haplotypes

We have recently identified two unrelated kindreds in which DR1 and DR2 co‐segregate as a single haplotype spanning several generations. Serology, PCR‐RFLP and sequence‐specific oligonucleotide probes were used to characterize the presence and segregation of the DRB1 and DRB5 loci in these two kindreds. In both families, the recombination resulted in co‐expression of a DRB1 locus that encoded a DR1 serologic phenotype and a DRB5 locus that encoded a “short” DR2 serologic phenotype. One of these kindreds co‐expressed the DR1 and DR15 (DRB5*01). The other kindred co‐expressed the DR1 and DR16 (DRB5*02). Our data indicate that the recombination event occurred in the region between the DRB1 locus and the DRB5 locus. This recombinant haplotype produces a DR2 phenotype which lacks the epitopes normally encoded by the DRB1 locus, resulting in a serologic “short” antigen. The clinical significance of such a recombinational event becomes evident when patients with such a genotype require allogeneic bone marrow transplantation. 1993 Blackwell Munksgaard