Contrasting features of urea cycle disorders in human patients and knockout mouse models.
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ABSTRACT:
SUBMITTER: Deignan JL
PROVIDER: S-EPMC2692509 | biostudies-literature | 2008 Jan
REPOSITORIES: biostudies-literature
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Contrasting features of urea cycle disorders in human patients and knockout mouse models.
Deignan Joshua L JL Cederbaum Stephen D SD Grody Wayne W WW
Molecular genetics and metabolism 20071022 1
The urea cycle exists for the removal of excess nitrogen from the body. Six separate enzymes comprise the urea cycle, and a deficiency in any one of them causes a urea cycle disorder (UCD) in humans. Arginase is the only urea cycle enzyme with an alternate isoform, though no known human disorder currently exists due to a deficiency in the second isoform. While all of the UCDs usually present with hyperammonemia in the first few days to months of life, most disorders are distinguished by a charac ...[more]
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Project description:UnlabelledBlood ammonia and glutamine levels are used as biomarkers of control in patients with urea cycle disorders (UCDs). This study was undertaken to evaluate glutamine variability and utility as a predictor of hyperammonemic crises (HACs) in UCD patients.MethodsThe relationships between glutamine and ammonia levels and the incidence and timing of HACs were evaluated in over 100 adult and pediatric UCD patients who participated in clinical trials of glycerol phenylbutyrate.ResultsThe median (range) intra-subject 24-hour coefficient of variation for glutamine was 15% (8-29%) as compared with 56% (28%-154%) for ammonia, and the correlation coefficient between glutamine and concurrent ammonia levels varied from 0.17 to 0.29. Patients with baseline (fasting) glutamine values >900 μmol/L had higher baseline ammonia levels (mean [SD]: 39.6 [26.2]μmol/L) than patients with baseline glutamine ≤ 900 μmol/L (26.6 [18.0]μmol/L). Glutamine values >900 μmol/L during the study were associated with an approximately 2-fold higher HAC risk (odds ratio [OR]=1.98; p=0.173). However, glutamine lost predictive significance (OR=1.47; p=0.439) when concomitant ammonia was taken into account, whereas the predictive value of baseline ammonia ≥ 1.0 upper limit of normal (ULN) was highly statistically significant (OR=4.96; p=0.013). There was no significant effect of glutamine >900 μmol/L on time to first HAC crisis (hazard ratio [HR]=1.14; p=0.813), but there was a significant effect of baseline ammonia ≥ 1.0 ULN (HR=4.62; p=0.0011).ConclusionsThe findings in this UCD population suggest that glutamine is a weaker predictor of HACs than ammonia and that the utility of the predictive value of glutamine will need to take into account concurrent ammonia levels.
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Project description:Nutritional management is essential for patients with inborn errors of metabolism, such as urea cycle disorders (UCDs). Lack of appetite is common in these patients and can lead to underconsumption of calories, catabolism, and subsequently loss of metabolic control. The etiology of anorexia in these patients is largely unexplored. The neuroendocrine hormone peptide tyrosine tyrosine (PYY), secreted postprandially from endocrine cells of the ileum and colon, induces feelings of satiety and decreases food intake. While plasma PYY levels have been characterized in a number of populations, they have not been examined in UCD patients. In a retrospective study, plasma PYY concentrations were measured in UCD (n=42) patients and controls (n=28) via an ELISA to determine if levels of this anorexigenic hormone are altered in this patient population. Median PYY levels were significantly higher in UCD patients compared to controls (p=3.5×10(-5)). Body mass index was significantly associated with increased PYY levels in controls (p=0.02), while UCD diagnosis subtype was associated with PYY levels (p=1×10(-3)) in cases. Median PYY levels were significantly lower in ornithine carbamoyltransferase deficient patients compared with all other UCD subtypes (p=9×10(-3)), but significantly higher compared to controls (p=1.6×10(-3)). Overall, this study demonstrates that UCD cases have increased PYY levels compared to controls, suggesting that regulation of PYY may be altered in these patients. These observations may lead to a better understanding of the development of anorexia in UCD patients.
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Project description:BackgroundUrea cycle disorders (UCDs) are among the most common inborn errors of liver metabolism. As therapies for hyperammonemia associated with urea cycle dysfunction have improved, chronic complications, such as liver disease, have become increasingly apparent in individuals with UCDs. Liver disease in UCDs may be associated with hepatic inflammation, hepatic fibrosis, portal hypertension, liver cancer and even liver failure. However, except for monitoring serum aminotransferases, there are no clear guidelines for screening and/or monitoring individuals with UCDs for liver disease. Thus, we systematically evaluated the potential utility of several non-invasive biomarkers for liver fibrosis in UCDs.MethodsWe evaluated grey-scale ultrasonography, liver stiffness obtained from shear wave elastography (SWE), and various serum biomarkers for hepatic fibrosis and necroinflammation, in a cohort of 28 children and adults with various UCDs.ResultsOverall, we demonstrate a high burden of liver disease in our participants with 46% of participants having abnormal grey-scale ultrasound pattern of the liver parenchyma, and 52% of individuals having increased liver stiffness. The analysis of serum biomarkers revealed that 32% of participants had elevated FibroTest™ score, a marker for hepatic fibrosis, and 25% of participants had increased ActiTest™ score, a marker for necroinflammation. Interestingly, liver stiffness did not correlate with ultrasound appearance or FibroTest™.ConclusionOverall, our results demonstrate the high overall burden of liver disease in UCDs and highlights the need for further studies exploring new tools for identifying and monitoring individuals with UCDs who are at risk for this complication.Trial registrationThis study has been registered in ClinicalTrials.gov (NCT03721367).
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