Citrullinemia type I is a rare, inherited condition in which the body cannot remove ammonia, a waste product of protein breakdown, from the blood. Because high ammonia can be harmful, newborn screening is important for catching it early so treatment can start quickly.
What causes citrullinemia type I
The condition is caused by variants in the ASS1 gene, part of the body's urea cycle, the system that clears ammonia. When the cycle does not work well, ammonia and a substance called citrulline build up. It is inherited in an autosomal recessive pattern.
How newborn screening detects it
Newborn screening measures amino acids in the heel-prick blood spot and flags an elevated citrulline level. An abnormal result prompts urgent confirmatory testing, including blood ammonia and plasma amino acid analysis.
How citrullinemia type I is managed
Management focuses on keeping ammonia low: a protein-controlled diet, medications that help the body remove ammonia (ammonia scavengers), and arginine supplementation. High-ammonia episodes are medical emergencies and are treated promptly. Care is directed by a metabolic specialist.
How genetic screening fits in
State newborn screening does an excellent job of catching citrullinemia type I. Genetic screening looks at the same picture from the DNA level and, in a single test, can also assess the genes tied to more than 1,000 other clinically actionable childhood conditions, many of which are not on any state panel. Fore Genomics offers an at-home cheek-swab screen, sequenced in CLIA-certified and CAP-accredited labs, with results supported by board-certified genetic counselors. See what we screen for or start screening.
Frequently asked questions
Is citrullinemia on newborn screening panels?
Yes. Citrullinemia type I is a core condition on the federal Recommended Uniform Screening Panel and is screened for across U.S. states.
Why does treatment need to happen quickly?
Because high blood ammonia can be harmful, early detection and prompt treatment are important. Families work closely with a metabolic team and follow an emergency plan.
Is it inherited?
Yes. Citrullinemia type I is autosomal recessive, so a child inherits an ASS1 variant from each parent.
Related guides
- Newborn Screening Guide (all conditions and states)
- Propionic Acidemia
- Maple Syrup Urine Disease (MSUD)
Medically reviewed by Fore's Clinical Team. This article is for general educational purposes and is not medical advice. Sources: HRSA Newborn Screening; National Organization for Rare Disorders (NORD).