Kidney transplantation across ABO-H incompatibility in a recipient with Bombay blood group: A novel report.

The Bombay blood group is an exceptionally rare phenotype characterized by the absence of H antigen on red blood cells due to mutations in the FUT1 gene and absence of H substance in secretions from concurrent FUT2 deficiency. These individuals produce potent anti-H antibodies in addition to anti-A and anti-B antibodies, posing unique challenges in transfusion and solid organ transplantation. We report a successful ABO-H-incompatible renal transplantation in a patient with genetically confirmed Bombay phenotype. A 30-year-old man with end-stage kidney disease secondary to immunoglobulin A nephropathy was evaluated for transplantation with his mother as a potential donor. Serologic and molecular studies identified a FUT1 homozygous missense variant (p.Leu242Arg) and a FUT2 homozygous deletion consistent with the classical digenic Bombay phenotype. The patient underwent a structured desensitization protocol with rituximab, plasma exchange, and intravenous immunoglobulin prior to transplantation. The postoperative course was uneventful, with stable graft function. This ground-breaking case demonstrates that, with appropriate desensitization, anti-H antibodies can be safely managed, thereby expanding the feasibility of renal transplantation in recipients with the Bombay phenotype.