Ornithine transcarbamylase deficiency: are carrier females suitable donors?

Role of liver transplantation in urea cycle disorders: Report from a nationwide study in Japan

Urea cycle disorders (UCDs) are inherited metabolic diseases causing hyperammonemia by defects in urea cycle enzymes or transporters. Liver transplantation (LT) currently is the only curative treatment option until novel therapies become available. We performed a nationwide questionnaire-based study between January 2000 and March 2018 to investigate the effect of LT in patients with UCDs in Japan. A total of 231 patients with UCDs were enrolled in this study. Of them, a total of 78 patients with UCDs (30 male and 16 female ornithine transcarbamylase deficiency (OTCD), 21 carbamoyl phosphate synthetase 1 deficiency (CPSD), 10 argininosuccinate synthetase deficiency (ASSD) and 1 arginase 1 deficiency (ARGD)) had undergone LT. Concerning the maximum blood ammonia levels at the onset time in the transplanted male OTCD (N = 28), female OTCD (N = 15), CPSD (N = 21) and ASSD (N = 10), those were median 634 (IQR: 277-1172), 268 (211-352), 806 (535-1382), and 628 (425-957) μmol/L, respectively. The maximum blood ammonia levels in female OTCD were thus significantly lower than in the other UCDs (all P < .01). LT was effective for long-term survival, prevented recurrent hyperammonemia attack, and lowered baseline blood ammonia levels in patients with UCDs. LT had limited effect for ameliorating neurodevelopmental outcome in patients with severe disease because hyperammonemia at the onset time already had a significant impact on the brain. Patients with ASSD may be more likely to survive without cognitive impairment by receiving early LT despite severe neonatal hyperammonemia ≥ 360 μmol/L. In patients with neonatal onset OTCD or CPSD, there may be additional factors with adverse effects on the brain that are not improved by LT.

Physical, cognitive, and social status of patients with urea cycle disorders in Japan

Urea cycle disorders (UCDs) are inherited metabolic diseases that lead to hyperammonemia. Severe hyperammonemia adversely affects the brain. Therefore, we conducted a nationwide study between January 2000 and March 2018 to understand the present status of UCD patients in Japan regarding diagnosis, treatments, and outcomes. A total of 229 patients with UCDs (126 patients: ornithine transcarbamylase deficiency [OTCD]; 33: carbamoyl phosphate synthetase 1 deficiency [CPS1D]; 48: argininosuccinate synthetase deficiency [ASSD]; 14: argininosuccinate lyase deficiency [ASLD]; and 8: arginase 1 deficiency [ARG1D]) were enrolled in the present study. Although growth impairment is common in patients with UCDs, we discovered that Japanese patients with UCDs were only slightly shorter than the mean height of the general adult population in Japan. Patients with neonatal-onset UCDs are more likely to experience difficulty finding employment and a spouse; however, some patients with late-onset UCDs were employed and married. Additionally, intellectual and developmental disabilities, such as attention deficit hyperactivity disorder (ADHD) and autism, hinder patients with UCDs from achieving a healthy social life. Moreover, we identified that it is vital for patients with UCDs presenting with mild to moderate intellectual disabilities to receive social support. Therefore, we believe the more robust social support system for patients with UCDs may enable them to actively participate in society.

Report of 3 Patients With Urea Cycle Defects Treated With Related Living-Donor Liver Transplant

Urea cycle defects are a group of metabolic disorders caused by enzymatic disruption of the urea cycle pathway, transforming nitrogen to urea for excretion from the body. Severe cases present in early infancy with life-threatening metabolic decompensation, and these episodes of hyperammonemia can be fatal or result in permanent neurologic damage. Despite the progress in pharmacologic treatment, long-term survival is poor especially for severe cases. Liver transplant is an alternative treatment option, providing sufficient enzymatic activity and decreasing the risk of metabolic decompensation. Three patients with urea cycle defects received related living-donor liver transplants at our hospital. Patients presented with late-onset ornithine transcarbamylase deficiency, argininosuccinate lyase deficiency, and citrullinemia. Maximum pretransplant ammonia levels were between 232 and 400 μmol/L (normal range is 18-72 μmol/L), and maximum posttransplant values were 52 to 94 μmol/L. All patients stopped medical treatment and dietary protein restriction for urea cycle defects after transplant. The patient with late-onset ornithine transcarbamylase deficiency already had motor deficits related to recurrent hyperammonemia attacks pretransplant. A major improvement could not be achieved, and he is wheelchair dependent at the age of 6 years. The other 2 patients had normal motor and mental skills before transplant, which have continued 12 and 14 months after transplant. Hepatic artery thrombosis in the patient with the ornithine transcarbamylase deficiency, intraabdominal infection in the patient with argininosuccinate lyase deficiency, and posterior reversible encephalopathy syndrome in the patient with citrullinemia were early postoperative complications. Histopathologic changes in livers explanted from patients with ornithine transcarbamylase deficiency and citrullinemia were nonspecific. The argininosuccinate lyase-deficient patient had portoportal fibrosis and cirrhotic nodule formation. In conclusion, liver transplant was a lifesaving procedure for our patients. Proper timing for transplant is important because high ammonia levels may result in permanent neurologic damage; however, transplant at younger ages also may increase morbidity.

Living donor liver transplantation for pediatric patients with metabolic disorders: the Japanese multicenter registry

LDLT is indicated for a variety of metabolic disorders, primarily in Asian countries due to the absolute scarcity of deceased donor LT. We analyzed data for all pediatric LDLTs performed between November 1989 and December 2010, during which 2224 pediatric patients underwent LDLT in Japan. Of these patients, 194 (8.7%) underwent LDLT for metabolic disorders. Wilson's disease (n = 59; 30.4%) was the most common indication in the patients with metabolic disorders, followed by OTCD (n = 40; 20.6%), MMA (n = 20; 10.3%), and GSD (n = 15; 7.7%). The one-, five-, 10-, and 15-yr patient and graft survival rates were 91.2%, 87.9%, 87.0%, and 79.3%, and 91.2%, 87.9%, 86.1%, and 74.4%, respectively. Wilson's disease and urea cycle deficiency were associated with better patient survival. The use of heterozygous donors demonstrated no negative impact on either the donors or recipients. With regard to X-linked OTCD, symptomatic heterozygote maternal donors should not be considered potential donor candidates. Improving the understanding of the long-term suitability of this treatment modality will require the registration and ongoing evaluation of all patients with inherited metabolic disease considered for LT.

Monogenic diseases that can be cured by liver transplantation

While the prevalence of most diseases caused by single-gene mutations is low and defines them as rare conditions, all together, monogenic diseases account for approximately 10 in every 1000 births according to the World Health Organisation. Orthotopic liver transplantation (LT) could offer a therapeutic option in monogenic diseases in two ways: by substituting for an injured liver or by supplying a tissue that can replace a mutant protein. In this respect, LT may be regarded as the correction of a disease at the level of the dysfunctional protein. Monogenic diseases that involve the liver represent a heterogeneous group of disorders. In conditions associated with predominant liver parenchymal damage (i.e., genetic cholestatic disorders, Wilson's disease, hereditary hemochromatosis, tyrosinemia, α1 antitrypsin deficiency), hepatic complications are the major source of morbidity and LT not only replaces a dysfunctional liver but also corrects the genetic defect and effectively cures the disease. A second group includes liver-based genetic disorders characterised by an architecturally near-normal liver (urea cycle disorders, Crigler-Najjar syndrome, familial amyloid polyneuropathy, primary hyperoxaluria type 1, atypical haemolytic uremic syndrome-1). In these defects, extrahepatic complications are the main source of morbidity and mortality while liver function is relatively preserved. Combined transplantation of other organs may be required, and other surgical techniques, such as domino and auxiliary liver transplantation, have been attempted. In a third group of monogenic diseases, the underlying genetic defect is expressed at a systemic level and liver involvement is just one of the clinical manifestations. In these conditions, LT might only be partially curative since the abnormal phenotype is maintained by extrahepatic synthesis of the toxic metabolites (i.e., methylmalonic acidemia, propionic acidemia). This review focuses on principles of diagnosis, management and LT results in both paediatric and adult populations of selected liver-based monogenic diseases, which represent examples of different transplantation strategies, driven by the understanding of the expression of the underlying genetic defect.