Diagnosis of adenine phosphoribosyltransferase deficiency as the underlying cause of renal failure in a renal transplant recipient

1Renal and Transplant Unit and 2Department of Pathology, Nottingham City Hospital NHS Trust, Nottingham and 3Purine Research Unit, Guy's Hospital, London, UK Adenine phosphoribosyltransferase (APRT) deficiency is a rare inborn error of metabolism first described in the UK in 1976 [1]. It is inherited as an autosomal recessive trait and the gene is located on chromosome 16. APRT is a salvage enzyme that normally catalyses the conversion of adenine to adenine monophosphate using PP-ribose-P. Deficiency results in adenine accumulation with conversion to and excretion of 2,8-dihydroxyadenine (2,8-DHA) in the urine. 2,8-DHA is protein-bound in plasma, but is extremely insoluble in urine at any pH. Tubular crystal deposition can occur associated with marked interstitial fibrosis and/or urolithiasis. Since its original description, APRT deficiency has been recognized increasingly as a cause of chronic renal failure. We report a case of APRT deficiency that was diagnosed after renal transplantation. This has led to specific treatment for the patient to reduce the risk of further crystal and stone formation in the transplanted kidney. Also, additional family members with the condition have been identified through family screening.