Ornithine transcarbamylase (OTC) deficiency

Diagnosis and Testing

How does someone get diagnosed with Ornithine Transcarbamylase Deficiency?

An ornithine transcarbamylase deficiency(OTC) diagnosis usually begins with clinical manifestations and laboratory studies during an illness episode that is affecting brain function (encephalopathy). During an episode abnormal lab values can include:

  • High blood plasma ammonia levels (>200 µmol/L)
  • Blood amino acid analysis revealing low citrulline and arginine levels and high glutamine.
  • High orotic acid levels in the urine organic acid analysis
  • Confirmation of the diagnosis of OTC in an affected individual requires ONE of the following findings:
  1. A disease-causing OTC gene change (pathogenic variant)
  2. Decreased OTC enzyme activity in the liver
  3. Family history of ornithine transcarbamylase deficiency AND elevated orotate in urine after an "allopurinol challenge test" OR (if the first two tests are normal, inconclusive, or not performed):
  4. Elevated orotate in urine after an allopurinol challenge test, which indicates reduced urea cycle function

SOURCE: Emory University - Department of Human Genetics in collaboration with ThinkGenetic • https://www.thinkgenetic.com/diseases/ornithine-transcarbamylase-deficiency/diagnosis-testing/18595 • DATE UPDATED: 2019-12-03


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