urea cycle disorders ( ucd ) are among the most common inborn errors of metabolism of the liver . citrullinemia can be classified into three types : neonatal / infantile ( types i and iii ) and the adult form ( type ii ) . more than 20 patients with citrullinemia have undergone liver transplantation , with favorable therapeutic results . however , the number of cases with auxiliary partial orthotopic liver transplantation ( apolt ) is limited . apolt was initially performed in patients with acute liver failure and non - cirrhotic metabolic liver disease to compensate for enzyme deficiencies without complete removal of the native liver and for small - for - size living donor grafts [ 3 - 5 ] . our patient was a 27-year - old man who was diagnosed with adult - onset type ii citrullinemia ( ctln2 ) at age 24 . the patient had been treated with a low protein diet and oral administration of lactulose . recently , the patient has had more frequent alterations of his mental status with irritability and altered consciousness . even though oral administration of l - arginine , kanamycin and intravenous hyperalimentation with branched chain amino acids was started , his plasma levels of ammonia and citrulline were highly elevated , up to 844 g / dl ( normal range , 19 to 87 g / dl ) and 682 mol / l ( normal range , 12 to 55 mol / l ) , respectively . despite the conservative medical treatment including alternative pathway medication , intermittent continuous renal replacement therapy and hemodialysis , his condition failed to improve . therefore , living donor liver transplantation was planned using a right lobe graft from his 25-year - old sister . however , the estimated volume of the donor 's right lobe was 800 ml compared to 180 ml of the left and in addition there was a type iii portal vein anomaly . we eventually decided to perform an apolt using the extended left lobe of the liver from the donor . the actual graft volume was 200 g and the graft - to - recipient weight ratio ( grwr ) was only 0.33% . the patient 's extended left lobe ( including caudate lobe ) was resected and the extended left lobe graft ( including middle and left hepatic vein ) was transplanted orthotopically . the left and middle hepatic vein trunk of the extended left lobe graft was anastomosed to the left and middle hepatic vein trunk of the recipient in end - to - end fashion with interposition venoplasty using the recipient 's greater saphenous vein as a patch . the left portal vein of the graft was anastomosed to that of the recipient in end - to - end fashion . considering that the graft was too small , the recipient 's right portal vein was narrowed by surgical clipping , instead of total diversion , for prevention of the development of portal venous hypertension . the left hepatic artery of the graft was anastomosed to that of the recipients in end - to - end fashion . intraoperative doppler ultrasonography demonstrated that portal and arterial blood flow were well maintained in both the native liver and the graft . on postoperative day 7 , abdominal computed tomography demonstrated orthotopically transplanted small left lobe graft with well - enhanced pattern ( fig . the post - operative course was uneventful and the patient was discharged without any problems . the plasma concentrations of ammonia were at the upper limits of normal , so only a low protein diet ( 50 g / day ) was supplied without any specific medication . on post - operative day 33 , the patient reported a sudden severe visual disturbance and the plasma levels of ammonia were noted to have increased up to 209 g / dl . the estimated computed tomography volume of the graft was decreased to 190 ml and a left portal vein stenosis was suspected . immediate coil embolization of 8th segmental branch of right anterior portal vein and self - expandable stent placement for left portal vein was performed in order to increase the portal flow to the graft ( fig . stent insertion day 7 , the calculated computed tomography volume of the graft was increased to 250 ml ( fig . apolt was initially introduced as a temporary or permanent support for patients with fulminant hepatic failure . apolt can provide an adequate hepatic mass to correct underlying enzyme deficiencies in adult patients with ucd . this procedure can be carried out to overcome the limitations of graft volume in living donor liver transplantation . in korea , therefore , living donor liver transplantation is the only treatment option for patients with metabolic liver disease such as ucd . in this case , the graft weight of 200 g and the grwr of 0.33% are the smallest graft and lowest margin ever reported to meet the minimum requirements for the demands of adequate metabolic function in adults . because the remaining native liver function , except for the metabolism of ammonia , is normal , the differential diagnosis including portal steal phenomenon and rejection as well as other problems associated with the vascular system is difficult . thus the plasma ammonia level is a valuable follow up marker and should be closely monitored in such patients . in addition , careful monitoring of the portal flow to the graft is important for the detection of delayed graft dysfunction . selective portal vein embolization is a useful method for the increase of portal flow to the graft . in conclusion , apolt can be a life saving procedure and an effective treatment for patients with adult - onset type ii citrullinemia , especially when a deceased donor graft is not available or when candidate donors have insufficient graft volume . however , further confirmation is needed with additional patients and long - term follow - up . how much volume of graft can be transplanted successfully is questionable in cases of inborn error of metabolism , such as ucd .
adult - onset type ii citrullinemia ( ctln2 ) is a disorder caused by an inborn error of metabolism affecting the liver . 
 ctln2 is an autosomal recessive disorder characterized by recurrent encephalopathy with hyperammonemia due to highly elevated plasma levels of citrulline and ammonia , caused by a deficiency of argininosuccinate synthetase in the liver . 
 a small number of patients have undergone liver transplantation with favorable results . in korea , the limitations of the deceased donor pool have made living donor liver transplantation a common alternative treatment option . 
 we report the case of a patient with type ii citrullinemia who was treated successfully with auxiliary partial orthotopic liver transplantation ( apolt ) from a living donor . 
 this is the first description of an apolt for a patient with adult onset type ii citrullinemia in korea .