Genetic and metabolic medicine
Urea cycle disorders including OTC deficiency
How urea cycle disorders present in adults, OTC deficiency in women and late-onset men, the ammonia sample and first-line metabolic tests, emergency management with glucose, scavengers and dialysis, drug triggers, citrin deficiency and other causes of non-hepatic hyperammonaemia.
Tier 2Condition
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- The urea cycle in hepatocytes converts ammonia into urea. A block lets ammonia and glutamine build up, causing astrocyte swelling and cerebral oedema. The biochemistry is in inborn errors of metabolism.
- OTC deficiency is the commonest urea cycle disorder (UCD) and the only X-linked one. The rest are autosomal recessive.
- Adults present with episodic encephalopathy, vomiting, behavioural change or psychosis after a catabolic or protein load, often misdiagnosed as psychiatric illness, drug intoxication or encephalitis.
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Sources
- Häberle J, Burlina A, Chakrapani A et al. Suggested guidelines for the diagnosis and management of urea cycle disorders: first revision. J Inherit Metab Dis 2019;42:1192-1230Journal of Inherited Metabolic Disease, 2019
- Urea cycle disorders overview (GeneReviews)University of Washington, Seattle (NCBI Bookshelf)
- Citrin deficiency (GeneReviews)University of Washington, Seattle (NCBI Bookshelf)
- PBS item 11865L: sodium phenylbutyrate granules (Pheburane), Streamlined Authority, urea cycle disordersAU/NZPharmaceutical Benefits Scheme, 2026
- AusPAR Carbaglu (carglumic acid)AU/NZTherapeutic Goods Administration, 2015
- Last updated
- 14 November 2026
What changed
- 14 November 2026 Personal emails, About story and Australian-style copy