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Start free with EleplanCitrullinemia type I
ORPHA:247525Disease
Also called ASS deficiency · Argininosuccinate synthase deficiency · Argininosuccinate synthetase deficiency · Argininosuccinic acid synthase deficiency · Argininosuccinic acid synthetase deficiency · CTLN1 · Citrullinemia type 1 · Classic citrullinemia
What it is
Citrullinemia type I is a rare autosomal recessive urea cycle defect characterized biologically by hyperammonemia and clinically by progressive lethargy, poor feeding and vomiting in the neonatal form (Acute neonatal citrullinemia type I) and by variable hyperammonemia in the later-onset form (Adult-onset citrullinemia type I).
Key facts
- Prevalence
- 1-9 / 100 000 (Europe)
- Age of onset
- All ages
- Inheritance
- Autosomal recessive
- Classified as
- Disease
Prevalence figures describe populations, not individuals, and are often estimates from a single study. Where the figure is an incidence or a birth prevalence, it says so.
Signs and symptoms
Sometimes5–29%
11- Abnormality of the nervous system
- Failure to thrive
- Feeding difficulties
- Hepatic encephalopathy
- Intellectual disability, borderline
- Intellectual disability, moderate
- Lethargy
- Respiratory alkalosis
and 3 more in this range
Rare1–4%
14- Ankle clonus
- Ataxia
- Coma
- Gastroesophageal reflux
- Headache
- Hypotonia
- Increased intracranial pressure
- Intellectual disability, mild
and 6 more in this range
These ranges are how often a sign appears across everyone diagnosed, not a prediction for one person — most people have some of these and not others. Orphanet also records findings that are specifically absent in this disease; those are in the data but not listed here.
Genes reported in subtypes
Orphanet records this gene on 2 more specific entries under this disorder, not on this entry itself:
A well-studied disease is usually split into subtypes, and the gene is curated on whichever one the evidence belongs to. Open a subtype to see which gene goes with it.
ICD-10 codes
ICD-10 has no distinct code for most rare diseases, so many are filed under the nearest available one. A shared code identifies the group, not this disease — the ORPHAcode above is what identifies it.
Related health topics
Reached through the ICD-10 categories this disease is filed under, so these describe the broader group rather than this disease specifically.
Cross-references
Orphadata Science: Free access data from Orphanet. © INSERM 1999. Data version 2026-06-23. Available under CC BY 4.0. This is a reference, not medical advice.
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