Classic Citrullinemia

Classic citrullinemia (CTLN1) is a disorder of the urea cycle characterized by neonatal or intermittent onset of hyperammonemia caused by a deficiency of the enzyme argininosuccinate synthetase. An acute neonatal form is the most common. Infants are normal at birth followed by an acute illness characterized by hyperammonemia, anorexia, vomiting, lethargy, and hepatomegaly in some cases, increased intracranial pressure, seizures and coma. A later onset presentation is less frequent and may be similar to or milder than the neonatal form and present with feeding difficulties, vomiting, episodic hyperammonemia, lethargy, seizures and cerebral atrophy on CT scans or MRI. CTLN1 has been diagnosed in adult women who developed severe symptoms such as psychosis during pregnancy or postpartum. Another late onset form, common in Japan, has been reported in individuals as late as 20 years of age with milder presentation including slurred speech, irritability and insomnia as presenting signs. Asymptomatic individuals have also been described.

Tests Available

Forms and Documents

Test Details

  • Confirmation of biochemical diagnosis
  • Carrier testing
  • Prenatal diagnosis in at risk pregnancies


4-5 weeks
2-5 mL Blood - Lavender Top Tube
Buccal Swabs

*Reporting times are typical, but could be extended in situations outside GeneDx's reasonable control.


  • 270.6 Disorders of urea cycle metabolism, Argininosuccinic aciduria, Citrullinemia, Disorders of metabolism of ornithine, citrulline, argininosuccinic acid, arginine, and ammonia, Hyperammonemia, Hyperornithinemia
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**The CPT codes provided are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payer being billed.


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  3. GeneTests
  4. Human Gene Mutation Database:
  5. Kobayashi, et al. (1995) Hum Genet 96:454- 463
  6. Engel et al. (2009) Hum Mutat 30:300-307