Atypical Recurrence of Adenine Phosphoribosyltransferase Deficiency-Associated Nephropathy After Kidney Transplant: A Case Report

Introduction: Adenine phosphoribosyltransferase (APRT) deficiency is a rare autosomal recessive disorder of purine metabolism leading to accumulation of 2,8-dihydroxyadenine (DHA) crystals. These crystals can cause nephrolithiasis, tubulointerstitial nephropathy, and progressive kidney failure. This case describes an atypical recurrence of DHA crystal nephropathy alongside acute cellular rejection. Case Description: A 24-year-old male with ESRD of 8 months duration with no history of nephrolithiasis, underwent kidney transplantation in 2024. Family history revealed consanguinity, with history of renal stones in paternal grandfather and maternal uncle. Pre-transplant workup showed HLA mismatch 2-0-1, negative crossmatches, mild proteinuria, and urate crystals in urine, but no nephrolithiasis or nephrocalcinosis on imaging. He received a living-donor kidney from his parentral aunt and was started on Anti-Thymocyte Globulin (ATG), tacrolimus, mycophenolate mofetil and prednisone. Initial graft function was good (creatinine 0.9 mg/dL by post operative day (POD) 3), but worsened by POD 15 (creatinine 1.5 mg/dL). Urinalysis showed persistent urate-like crystals, with normal serum uric acid. Renal biopsy revealed acute T-cell–mediated rejection (Banff IIB). C4d was negative, but DHA crystals were identified, confirming recurrent APRT-related nephropathy. He was initially treated with pulse steroids and additional 3 doses of ATG for presumed rejection. After APRT deficiency was confirmed, febuxostat (80 mg/day) was started. Renal function improved (creatinine 1.3 mg/dL), with gradual crystalluria resolution. Discussion: APRT deficiency is a rare but significant cause of recurrent nephropathy, often misdiagnosed as uric acid nephropathy due to radiolucent DHA crystals, leading to delayed treatment and early graft dysfunction. Early diagnosis and initiation of xanthine oxidase inhibitors are crucial for preserving graft function. This case raises awareness about APRT deficiency-associated nephropathy as a potential cause of early graft dysfunction post-transplant. Misdiagnosis as rejection can lead to inappropriate treatment.