*Purpose: We report an interesting case of delayed graft function following pediatric liver transplantation, which was attributed to previously unrecognized urea cycle carrier genetic defect in the allograft liver.

*Methods: This is a retrospective chart review.

*Results: A 5 month old African-American female infant with blood type AB+ underwent whole organ ABO-compatible deceased donor liver transplantation for unpalliated biliary atresia. The donor was a 17 month old African-American female infant, blood type A+, with no significant past medical history. The transplant operation itself was uncomplicated and only the skin layer of the abdomen was closed. The recipient was extubated on post-operative day (POD) 1, however, later that day was somnolent and hyperreflexic concerning for hepatic encephalopathy. Laboratory values were concerning for primary nonfunction of the allograft, with ALT 2397, AST 3318, INR 6.68, Ammonia 144, and lactate was normal. The recipient was re-intubated and continuous renal replacement therapy for clearance of ammonia was initiated on POD2-4. The recipient was listed for retransplantation at status 1A for primary nonfunction. However, lab indices slowly improved with ammonia level 36, AST 37, ALT 271, and INR 1.03 by POD6. The recipient returned to the OR on POD 6 for fascial closure. An opportunistic liver biopsy showed steroid effect on hepatocytes, normal liver architecture, mild canalicular cholestasis, and no evidence of hepatocyte necrosis or acute cellular rejection. The recipient’s allograft function slowly recovered and she was removed from the transplant list. Due to hyperammonemia despite CRRT, the question was raised regarding a potential urea cycle defect present in the allograft liver. After communicating with the organ procurement organization, DNA was obtained from remaining donor PBMC. Genetic testing for urea cycle defects was performed, which showed that the donor liver carried a heterozygous pathogenic mutation in the ASL gene encoding the urea cycle enzyme, arginosuccinase. This enzyme catalyzes the breakdown of arginosuccinate into fumarate and arginine. Individuals who are homozygous for ASL mutations have frequent metabolic crises in response to catabolic states including illness and fasting. Carriers can also have crises under extreme metabolic stress. It is thought that the ischemia-reperfusion stress on the allograft liver led to a metabolic crisis in the recipient that masqueraded as primary nonfunction. With supportive care the recipient made a full recovery. LFT normalized and she was discharged from the hospital on POD 39.

*Conclusions: When faced with rare complications following liver transplantation including primary nonfunction, metabolic liver disease within the allograft should be considered. Genetic testing on remaining DNA from the donor can confirm the presence of metabolic disease.

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