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      Frequency and Pathophysiology of Acute Liver Failure in Ornithine Transcarbamylase Deficiency (OTCD)

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          Abstract

          Background

          Acute liver failure (ALF) has been reported in ornithine transcarbamylase deficiency (OTCD) and other urea cycle disorders (UCD). The frequency of ALF in OTCD is not well-defined and the pathogenesis is not known.

          Aim

          To evaluate the prevalence of ALF in OTCD, we analyzed the Swiss patient cohort. Laboratory data from 37 individuals, 27 females and 10 males, diagnosed between 12/1991 and 03/2015, were reviewed for evidence of ALF. In parallel, we performed cell culture studies using human primary hepatocytes from a single patient treated with ammonium chloride in order to investigate the inhibitory potential of ammonia on hepatic protein synthesis.

          Results

          More than 50% of Swiss patients with OTCD had liver involvement with ALF at least once in the course of disease. Elevated levels of ammonia often correlated with (laboratory) coagulopathy as reflected by increased values for international normalized ratio (INR) and low levels of hepatic coagulation factors which did not respond to vitamin K. In contrast, liver transaminases remained normal in several cases despite massive hyperammonemia and liver involvement as assessed by pathological INR values. In our in vitro studies, treatment of human primary hepatocytes with ammonium chloride for 48 hours resulted in a reduction of albumin synthesis and secretion by approximately 40%.

          Conclusion

          In conclusion, ALF is a common complication of OTCD, which may not always lead to severe symptoms and may therefore be underdiagnosed. Cell culture experiments suggest an ammonia-induced inhibition of hepatic protein synthesis, thus providing a possible pathophysiological explanation for hyperammonemia-associated ALF.

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          Most cited references34

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          Fate tracing of mature hepatocytes in mouse liver homeostasis and regeneration.

          Recent evidence has contradicted the prevailing view that homeostasis and regeneration of the adult liver are mediated by self duplication of lineage-restricted hepatocytes and biliary epithelial cells. These new data suggest that liver progenitor cells do not function solely as a backup system in chronic liver injury; rather, they also produce hepatocytes after acute injury and are in fact the main source of new hepatocytes during normal hepatocyte turnover. In addition, other evidence suggests that hepatocytes are capable of lineage conversion, acting as precursors of biliary epithelial cells during biliary injury. To test these concepts, we generated a hepatocyte fate-tracing model based on timed and specific Cre recombinase expression and marker gene activation in all hepatocytes of adult Rosa26 reporter mice with an adenoassociated viral vector. We found that newly formed hepatocytes derived from preexisting hepatocytes in the normal liver and that liver progenitor cells contributed minimally to acute hepatocyte regeneration. Further, we found no evidence that biliary injury induced conversion of hepatocytes into biliary epithelial cells. These results therefore restore the previously prevailing paradigms of liver homeostasis and regeneration. In addition, our new vector system will be a valuable tool for timed, efficient, and specific loop out of floxed sequences in hepatocytes.
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            A longitudinal study of urea cycle disorders.

            The Urea Cycle Disorders Consortium (UCDC) is a member of the NIH funded Rare Diseases Clinical Research Network and is performing a longitudinal study of 8 urea cycle disorders (UCDs) with initial enrollment beginning in 2006. The consortium consists of 14 sites in the U.S., Canada and Europe. This report summarizes data mining studies of 614 patients with UCDs enrolled in the UCDC's longitudinal study protocol. The most common disorder is ornithine transcarbamylase deficiency, accounting for more than half of the participants. We calculated the overall prevalence of urea cycle disorders to be 1/35,000, with 2/3rds presenting initial symptoms after the newborn period. We found the mortality rate to be 24% in neonatal onset cases and 11% in late onset cases. The most common precipitant of clinical hyperammonemic episodes in the post-neonatal period was intercurrent infections. Elevations in both blood ammonia and glutamine appeared to be biomarkers for neurocognitive outcome. In terms of chronic treatment, low protein diet appeared to result in normal weight but decreased linear growth while N-scavenger therapy with phenylbutyrate resulted in low levels of branched chain amino acids. Finally, we found an unexpectedly high risk for hepatic dysfunction in patients with ornithine transcarbamylase deficiency. This natural history study illustrates how a collaborative study of a rare genetic disorder can result in an improved understanding of morbidity and disease outcome.
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              Genotype spectrum of ornithine transcarbamylase deficiency: correlation with the clinical and biochemical phenotype.

              Ornithine transcarbamylase (OTC) deficiency, a partially dominant X-linked disorder, is the most common inherited defect of the urea cycle. Previous reports suggested a variable phenotypic spectrum, and several studies documented different "private" mutations in the OTC genes of patients. Our laboratory identified disease-causing mutations in 157 families with OTC deficiency, 100 of which came to medical attention through a hemizygous propositus and in 57 the index case was a heterozygous female. We correlated the genotype with age of onset, liver OTC activity, incorporation of nitrogen into urea, and peak plasma ammonia levels. The "neonatal onset" group has a homogeneous clinical and biochemical phenotype, whereas the "late onset" group shows an extremely wide phenotype; 60% of the mutations are associated exclusively with acute neonatal hyperammonemic coma. The remaining mutations caused a nonuniform phenotype ranging from severe disease to no symptoms; 31% of the mutations in the OTC gene occur in CpG dinucleotides (methylation-mediated deamination), and none of them accounted for more than 4% of the total. Eighty-six percent of the mutations represented single-base substitutions and 68% of the substitutions were transitions. G-to-A and C-to-T transitions were the most frequent substitutions (34 and 21%, respectively) whereas C-to-A, A-to-C, C-to-G, and T-to-A transversions were the least common (1.5-3%). Twenty percent of propositi and 77% of propositae carried new mutations. Forty percent of female germinal mutations were in CpG dinucleotides whereas this number appears much smaller in male germinal mutations. These data allow classification of patients with OTC deficiency into at least two groups who have discordant disease course and prognoses. In addition, they improve our understanding on the origin of mutations in the OTC gene and allow better counseling of affected families.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, CA USA )
                1932-6203
                12 April 2016
                2016
                : 11
                : 4
                : e0153358
                Affiliations
                [1 ]Division of Metabolism and Children`s Research Center (CRC), University Children`s Hospital, Zurich, Switzerland
                [2 ]radiz–Rare Disease Initiative Zurich, Clinical Research Priority Program for Rare Diseases, University of Zurich, Zurich, Switzerland
                [3 ]Department of Pediatrics, Medical Genetics, University of California San Francisco, San Francisco, United States of America
                [4 ]Department of Clinical Research and Clinic for Visceral Surgery and Medicine, Bern University Hospital, Bern, Switzerland
                [5 ]Department of Pediatrics, University Children's Hospital, Bern, Switzerland
                [6 ]University Institute of Clinical Chemistry, University of Bern, Bern, Switzerland
                [7 ]Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland
                National Institutes of Health, UNITED STATES
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                Conceived and designed the experiments: AL RCG AK TS MG JMN MRB JH. Performed the experiments: AL AK. Analyzed the data: AL RCG AK TS MG JMN MRB JH. Contributed reagents/materials/analysis tools: AL RCG AK TS MG JMN MRB JH. Wrote the paper: AL RCG MRB JH.

                Article
                PONE-D-16-06926
                10.1371/journal.pone.0153358
                4829252
                27070778
                ec18c20b-d50d-4b97-8644-e5b0d8f72c52
                © 2016 Laemmle et al

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 17 February 2016
                : 29 March 2016
                Page count
                Figures: 4, Tables: 4, Pages: 15
                Funding
                Funded by: EMDO Stiftung Zurich
                Award ID: Grant 851
                Award Recipient :
                Funded by: Forschungszentrum Kind (FZK) – University Children`s Hospital Zurich
                Award ID: Grant 10511
                Award Recipient :
                Funded by: funder-id http://dx.doi.org/10.13039/501100001711, Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung;
                Award ID: 310030_153196
                Award Recipient :
                Funded by: Rare Disease Initiative Zurich (radiz)
                Award Recipient :
                Funded by: National Institutes of Health (NIH) Rare Disease Clinical Research Network (RDCRN)
                Award ID: U54HD061221
                Funded by: Office of Rare Diseases Research
                Funded by: the National Center for Advancing Translational Science
                Funded by: Eunice Kennedy Shriver National Institute of Child Health and Human Development
                Funded by: O’Malley 332 Foundation
                Funded by: the Rotenberg Family Fund
                Funded by: the Dietmar-Hopp Foundation
                Funded by: the Kettering Fund
                Funded by: EMDO Stiftung Zurich
                Award ID: Grant 851
                Award Recipient :
                Funded by: Rare Disease Initiative Zurich (radiz)
                Award Recipient :
                This work was supported by the “EMDO Stiftung Zurich” (grant 851 to JH and AL), by the “Forschungszentrum Kind (FZK) – University Children`s Hospital Zurich” (grant 10511 to AL), and by the Swiss National Science Foundation (grant 310030_153196 to JH). AL and MRB are supported by the Rare Disease Initiative Zurich (radiz), a clinical research priority program for rare diseases of the University of Zurich, Switzerland. The Urea Cycle Disorders Consortium (UCDC; U54HD061221) is a part of the National Institutes of Health (NIH) Rare Disease Clinical Research Network (RDCRN), supported through collaboration between the Office of Rare Diseases Research (ORDR), the National Center for Advancing Translational Science (NCATS and the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD). The Urea Cycle Disorders Consortium is also supported by the O’Malley Foundation, the Rotenberg Family Fund, the Dietmar-Hopp Foundation, and the Kettering Fund. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Research Article
                Physical Sciences
                Chemistry
                Chemical Compounds
                Ammonia
                Biology and Life Sciences
                Cell Biology
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