Primary Hyperoxaluria Type 1 Diagnosed After Kidney Transplantation in the Absence of Classical Features.

Background: Primary hyperoxaluria Type 1 is a rare inherited metabolic disorder caused by pathogenic variants in the AGXT gene. Because the disorder leads to excessive internal oxalate formation, progressive end-stage kidney disease (ESKD) may occur. While most affected individuals present during childhood, a subset is diagnosed only later in adult life, frequently after substantial renal deterioration. Delayed diagnosis increases the risk of recurrent oxalate nephropathy and graft dysfunction following kidney transplantation. Case Presentation: We report a 30-year-old woman with ESKD of unknown aetiology who underwent living-donor kidney transplantation. One year later, during a subsequent pregnancy, she developed progressive graft dysfunction. Kidney biopsy demonstrated extensive calcium oxalate crystal deposition, raising suspicion for an underlying metabolic disorder. Genetic testing subsequently confirmed a pathogenic AGXT mutation, establishing the diagnosis of adult-onset PH1. Urinary oxalate concentrations were within normal limits before and after transplantation, emphasizing the diagnostic challenge. Conclusion: This case highlights the importance of considering PH1 in adults with unexplained chronic or ESKD, even in the absence of classical features or elevated urinary oxalate excretion. Early genetic testing and careful assessment of family history are essential for timely diagnosis, enabling appropriate transplant planning, disease-specific therapy, and genetic counselling.