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Disorder of Ornithine Metabolism



  • Male hemizygotes usually present in infancy, while female heterozygotes may be totally asymptomatic.[path.upmc.edu]
  • Later in life, the disease may present in both males and females. In the classic presentation, a male infant appears well initially, but by the second day of life becomes irritable, lethargic, and stops feeding.[en.wikipedia.org]
  • Male and female infant or childhood presentations have been reported with vomiting, irritability, and failure to thrive, often triggered by illnesses.[clinicaladvisor.com]
  • Rarely, OAT-deficient neonates present with hyperammonaemic encephalopathy due to impaired urea cycle function caused by substrate limitation, with associated hypoargininaemia and hypoornithinaemia.[jhu.pure.elsevier.com]
  • Males usually present in the neonatal period with massively elevated ammonia levels and hyperammonemic coma, encephalopathy and respiratory alkalosis.[genedx.com]
  • Among the surviving school-aged children, three had normal schooling and two had remedial schooling due to specific learning disabilities (dyslexia, deficits in executive function, attention deficit or hyperactivity).[ojrd.biomedcentral.com]
Broad Nasal Bridge
  • الصفحة 53 - Infants with ZS present in the neonatal period with characteristic dysmorphic features (prominent forehead, large anterior fontanelle, broad nasal bridge, epicanthal folds, high arched palate, micrognathia, redundant neck skin folds, clinodactyly[books.google.com]
  • الصفحة 53 - Neurological abnormalities are prominent, including severe hypotonia, areflexia, poor suck rellex and seizures. Neuronal migration defects may be observed on neuroimaging.[books.google.com]
Alteration of Consciousness
  • The first symptoms were mostly neurological (49/52 patients) and included alterations in consciousness (31/52), global hypotonia (10/52), ataxia (2/52), and acute neurological regression (2/52).[ojrd.biomedcentral.com]
  • Other features, such as corneal clouding, cataracts, pigmentary retinopathy, polycystic kidneys, cryptorchidism, dislocated hips and stippled epiphyses on radiographs (chondrodysplasia punctata) may be present.[books.google.com]


  • Most of these heterozygous female patients (approximately 80% in the literature) are apparently asymptomatic and present a normal biochemical workup (notably, ammonemia and plasma glutamine).[ojrd.biomedcentral.com]


  • Biochemistry of Ornithine Transcarbamylase Deficiency and Its Treatment.[nejm.org]
  • There is currently one approved treatment for ornithine transcarbamylase deficiency.[raredr.com]
  • Inborn Metabolic Diseases: Diagnosis and Treatment. Springer Berlin Heidelberg, 2012. p. 323-332.[jhu.pure.elsevier.com]
  • TREATMENT Treatment is directed toward preventing increased ammonia production through a protein-restricted diet, avoidance of catabolic states and supplementation of citrulline.[obgynkey.com]
  • Some babies may also need additional treatments if there are complications. [ Read More ][icdlist.com]


  • Prognosis is less clear in cases of adult onset OTCD, as detection of the disease is almost universally post symptomatic [2].[house.wikia.com]
  • Prenatal diagnosis is possible by molecular testsing Repeatedly reinforcing the parents in their abilities to perceive early signs of hyperammonemia and to take immediate steps to obtain medical care can be life saving.(5) Prognosis: Prognosis for older[path.upmc.edu]
  • […] patients will often present with headaches, nausea, vomiting, delirium, erratic behavior, or seizures. [2] A detailed dietary history of an affected individual with undiagnosed OTC deficiency will often reveal a history of protein avoidance. [4] The prognosis[en.wikipedia.org]
  • Prognosis With early diagnosis and appropriate therapy the prognosis is good, but because the disorder is mild, diagnostic delay is common and some neurological damage may be sustained.[orpha.net]
  • Prognosis Acute recovery: Outcomes are less severe if ammonia concentration remains Long-term complications : Poor growth, developmental delay, mental retardation, ADHD, seizure disorder, CP.[pedclerk.bsd.uchicago.edu]


  • Etiology MSUD is due to mutations in genes encoding 3 of the 4 subunits of the branched chain 2-ketoacid dehydrogenase (BCKAD) complex.[orpha.net]
  • Etiology of Urea Cycle Defects Urea cycle defects result from a deficiency or total absence of the activity of any of the enzymes along the pathway, particularly carbamoyl phosphate synthetase I (CPSI), ornithine transcarbamylase (OTC), arginosuccinate[pedclerk.bsd.uchicago.edu]
  • The etiology of the encephalopathy was not suspected until hyperammonemia (137 μ/L) was observed. Lactulose treatment produced no improvement in clinical signs, and the patient remained in a deep coma, with ammonia levels elevated up to 254 μ/L.[jintensivecare.biomedcentral.com]


  • Epidemiology: The estimated incidence of 1:80,000 live births may be an underestimation because late onset cases may go undetected. In older individuals, the initial onset can occur at any age up to 40-50 years and beyond.[path.upmc.edu]
  • Summary Epidemiology The estimated birth prevalence of MSUD is 1/ 150,000. Around 30% of cases are believed to be of the intermediate type.[orpha.net]
  • Genatlas disease for OTC Gene neonatal distress and hyperammonemia,including late-onset hyperammonemic coma Relevant External Links for OTC Genetic Association Database (GAD) OTC Human Genome Epidemiology (HuGE) Navigator OTC Atlas of Genetics and Cytogenetics[genecards.org]
  • Table 1 Epidemiological characteristics of the patients Number of cases 27 52 11 Males 22 21 5 females 5 31 6 Number of deceased 20 7 1 at diagnosis 13 5 1 during follow up 7 2 0 Number of decompensations per patient (and relative to mean length of follow-up[ojrd.biomedcentral.com]
Sex distribution
Age distribution


  • Pathophysiologically, OAT catalyzes the conversion of ornithine to Δ 1 -pyrroline-5-carboxylate (P5C). Normally the reaction equilibrium is directed toward the production of P5C.[obgynkey.com]
  • FINAL DIAGNOSIS: PARTIAL ORNITHINE TRANSCARBAMYLASE (OTC) DEFICIENCY Pathophysiology: OTC deficiency is the most common of the urea cycle disorders (UCD).(1).[path.upmc.edu]
  • Pathophysiology OTC deficiency is one of the proximal urea cycle defects and is due to a complete or partial deficiency of the mitochondrial enzyme ornithine transcarbamylase (OTC) which combines ornithine and carbamylphosphate to form citrulline (as[newenglandconsortium.org]
  • Although hyperammonemia is the primary cause of mortality and morbidity in these disorders, some of them point to unrelated pathophysiological processes.[news-medical.net]
  • […] administration of allopurinol or a protein load to identify OTC carriers Genetics Test Information Provides information that may help with selection of the correct genetic test or proper submission of the test request Clinical Information Discusses physiology, pathophysiology[mayomedicallaboratories.com]


  • Liver transplantation cannot cure brain damage which has already occurred, but it will prevent future hyperammonemic episodes and prevent further damage. [1] References [ edit ] a b c d e f Wraith, J. E. (2001).[en.wikipedia.org]
  • Rapid control of the hyperammonemia is crucial in preventing or lessening the degree of mental retardation.[newenglandconsortium.org]
  • Treatment Since the disease results in an inability to handle large amounts of nitrogen load, the treatment includes strategies to decrease the intake of nitrogen (low-protein diet), prevention of excessive body protein breakdown during acute illnesses[house.wikia.com]
  • Ammonia toxicity and its prevention in inherited defects of the urea cycle. Diabetes Obes Metab. Sep 2009;11(9):823-35. Crosbie DC, Sugumar H, Simpson MA, Walker SP, Dewey HM, Reade MC.[rarediseases.org]
  • TREATMENT Treatment is directed toward preventing increased ammonia production through a protein-restricted diet, avoidance of catabolic states and supplementation of citrulline.[obgynkey.com]

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