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Genetic and Rare Diseases Information Center (GARD)

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Citrullinemia type I

Other Names for this Disease
  • Argininosuccinate synthetase deficiency
  • ASS deficiency
  • Citrullinemia 1
  • Citrullinuria
  • Classic citrullinemia
More Names
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What causes citrullinemia type I?

Citrullinemia type I is caused by mutations in the ASS1 gene.[1] This gene provides instructions for making an enzyme, argininosuccinate synthetase 1, that is responsible for the third step in the urea cycle.[1][2] Mutations in the ASS1 gene reduce the activity of the enzyme, which disrupts the urea cycle and prevents the body from processing nitrogen effectively. Excess nitrogen (in the form of ammonia) and other byproducts of the urea cycle accumulate in the bloodstream. Ammonia is particularly toxic to the nervous system, which helps explain the neurologic symptoms (such as lethargy, seizures, and ataxia) that are often seen in this condition.[1]
Last updated: 4/20/2010

  1. Citrullinemia. Genetics Home Reference (GHR). 2006; Accessed 7/11/2011.
  2. Thoene JG. Citrullinemia Type I. GeneReviews. 2009; Accessed 4/20/2010.