In situ hybridization for the Y chromosome reveals a donor origin for a posttransplant lymphoproliferative disorder in a sex-mismatched hepatic allograft.

We report a case of posttransplant lymphoproliferative disorder diagnosed within 4 weeks of orthotopic liver transplantation from a male donor to a female recipient. To determine whether the posttransplant lymphoproliferative disorder was of donor or recipient origin, nonisotopic in situ hybridization for the human Y chromosome was performed on formalin-fixed, paraffin-embedded sections of the donor liver using a digoxigenin-labeled probe. The lymphoid cells hybridized with the Y chromosome probe, indicative of a male genotype consistent with posttransplant lymphoproliferative disorder of donor origin. This case illustrates that nonisotopic in situ hybridization for the Y chromosome can discriminate between donor and recipient cells in sex-mismatched organ transplants.