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Purpose: Liver transplantation (LTx) is performed in individuals with urea cycle disorders when medical management (MM) insufficiently prevents the occurrence of hyperammonemic events. However, there is a paucity of systematic analyses on the effects of LTx on health-related outcome parameters compared to individuals with comparable severity who are medically managed. Methods: We investigated the effects of LTx and MM on validated health-related outcome parameters, including the metabolic disease course, linear growth, and neurocognitive outcomes. Individuals were stratified into “severe” and “attenuated” categories based on the genotype-specific and validated in vitro enzyme activity. Results: LTx enabled metabolic stability by prevention of further hyperammonemic events after transplantation and was associated with a more favorable growth outcome compared with individuals remaining under MM. However, neurocognitive outcome in individuals with LTx did not differ from the medically managed counterparts as reflected by the frequency of motor abnormality and cognitive standard deviation score at last observation. Conclusion: Whereas LTx enabled metabolic stability without further need of protein restriction or nitrogen-scavenging therapy and was associated with a more favorable growth outcome, LTx—as currently performed—was not associated with improved neurocognitive outcomes compared with long-term MM in the investigated urea cycle disorders.

ollaborators: Bloxam S, Brody L, Caspi L, Elsbecker S, Fierro L, Lynn A, Mullins M, Mütze U, Papaleo C, Payan I, Seminara J, Simpson K, Singer R, Wallis K, Alber FD, Babikian T, Bender H, Boys C, Breiger D, Buerger C, Caudle SE, NguyenDriver M, Kerr E, Mamak E, Sanz JH, Tangen R, Wilkening G, Cederbaum S, Feigenbaum A, Kerr DS, LichterKonecki U, Seashore MR, Berry SA, Burrage L, Coughlin C, Diaz GA, Gallagher RC, Gropman A, Harding CO, Lee B, Le Mons C, Lawrence Merritt J 2nd, Nagamani SCS, Schulze A, Stricker T, Tuchman M, Waisbren S, WeisfeldAdams J, Wong D, Yudkoff M, Arnoux J, Bari Cacute I, Bosch AM, Chabrol B, Chakrapani A, CortèsSaladefont E, Couce ML, Eyskens F, de Laet C, de Meirleir L, Freisinger P, Gleich F, Grünewald S, Häberle J, Hwu W, Jalan A, Karall D, Lindner M, Lund AM, Martinelli D, Murphy E, Mühlhausen C, Olivieri G, Ottolenghi C, Rodrigues E, Rubert L, Sarajlija A, Schiff M, Sokal E, SykutCegielska J, Walter JH, Williams M, Zeman J. BACKGROUND: To improve our understanding of urea cycle disorders (UCDs) prospectively followed by two North American (NA) and European (EU) patient cohorts. AIMS: Description of the NA and EU patient samples and investigation of the prospects of combined and comparative analyses for individuals with UCDs. METHODS: Retrieval and comparison of the data from 1095 individuals (NA: 620, EU: 475) from two electronic databases. RESULTS: The proportion of females with ornithine transcarbamylase deficiency (fOTC-D), particularly those being asymptomatic (asfOTC-D), was higher in the NA than in the EU sample. Exclusion of asfOTC-D resulted in similar distributions in both samples. The mean age at first symptoms was higher in NA than in EU patients with late onset (LO), but similar for those with early (≤ 28 days) onset (EO) of symptoms. Also, the mean age at diagnosis and diagnostic delay for EO and LO patients were similar in the NA and EU cohorts. In most patients (including fOTC-D), diagnosis was made after the onset of sym

Objective Citrullinemia type 1 (CTLN1) is an inherited metabolic disease affecting the brain which is detectable by newborn screening. The clinical spectrum is highly variable including individuals with lethal hyperammonemic encephalopathy in the newborn period and individuals with a mild‐to‐moderate or asymptomatic disease course. Since the phenotypic severity has not been predictable early during the disease course so far, we aimed to design a reliable disease prediction model. Methods We used a newly established mammalian biallelic expression system to determine residual enzymatic activity of argininosuccinate synthetase 1 (ASS1; OMIM #215700) in 71 individuals with CTLN1, representing 48 ASS1 gene variants and 50 different, mostly compound heterozygous combinations in total. Residual enzymatic ASS1 activity was correlated to standardized biochemical and clinical endpoints available from the UCDC and E‐IMD databases. Results Residual enzymatic ASS1 activity correlates with peak plasma ammonium and L‐citrulline concentrations at initial presentation. Individuals with 8% of residual enzymatic ASS1 activity or less had more frequent and more severe hyperammonemic events and lower cognitive function than those above 8%, highlighting that residual enzymatic ASS1 activity allows reliable severity prediction. Noteworthy, empiric clinical practice of affected individuals is in line with the predicted disease severity supporting the notion of a risk stratification‐based guidance of therapeutic decision‐making based on residual enzymatic ASS1 activity in the future. Interpretation Residual enzymatic ASS1 activity reliably predicts the phenotypic severity in CTLN1. We propose a new severity‐adjusted classification system for individuals with CTLN1 based on the activity results of the newly established biallelic expression system.