Citrullinaemia

Alternative name Argininosuccinic acid synthetase (ASAS) deficiency
About the condition Citrullinaemia is an amino acid disorder. It is caused by a missing enzyme from the urea cycle. Infants with this disorder are not able to convert ammonia into urea. Ammonia accumulates in the body and is toxic to the brain. Ammonia is a waste-product and is normally produced during the breakdown of protein from food or muscle.
Inheritance Autosomal recessive
Year screening started in WA 2005
Incidence in Australia Approximately 1 in 100,000 births
Enzyme defect Urea cycle disorder
Symptoms if untreated This disorder usually causes toxic levels of blood ammonia in the first days of life. This can lead to vomiting, lethargy, seizures, coma and death. There are also some less severe forms, which can cause intellectual disability and may go undetected for months or years.
Metabolites on bloodspot screening
  • Increased citrulline
  • Increased citrulline/phenylalanine ratio
Diagnostic tests
  • Plasma ammonia
  • Plasma amino acids
  • Urine amino and organic acids
  • ASS1 gene analysis
Treatment
  • Dialysis is sometimes needed to acutely lower the blood ammonia
  • Protein-restricted diet
  • Sodium benzoate and/or sodium phenylacetate
  • Arginine supplementation
Screening issues Citrullinaemia and argininosuccinic aciduria are the only urea cycle disorders detected by this screening strategy.