LAUSR

A 47-year-old Vietnamese man with prior failed renal allograft is selected for evaluation of a kidney from a deceased African American donor. Flow crossmatch with current and archived patient serum are negative. The antibody screen (SA Luminex assay) reveals Class I and II sensitizations but no DSA. Upon further analysis, however, there is concern for lab error based on well-established DR-DQ associations. The donor’s HLA typing includes DR7, DR8, DQ7, DQ8 – an unexpected pattern. DR7 is typically inherited with either DQ2 or DQ9; DR8 with DQ4, DQ6, or DQ7. Inheritance of both DR7 and DQ8 calls into question the validity of the results. This is particularly concerning given the patient’s very high level of sensitization to DQ2 (MFI 18780). Donor typing is repeated by SSP, confirming the initial rSSO results. Repeat cross match is negative. Transplantation proceeds. This case highlights unexpected HLA associations that can arise due to rare crossover events during meiosis. The probability of inheriting DQ8 along with DR7 is low, based on the close proximity of genes DRB1 and DQB1 within chromosome 6. According to allelefrequencies.net, the frequency of a haplotype containing DR7-DQ8 within an African American population is about 0.22%. We estimate the probability of meiotic crossover between DRB1 and DQB1 as 0.03%. While we do not have parental HLA typing for the deceased donor, he likely inherited DQ8 from a parent carrying DR4. Regardless of the origin of the donor’s DQ8, this case also illustrates the importance of questioning uncommon results, and performing confirmation with alternate testing modalities when such results present themselves.