Hyperammonemia i (carbamyl phosphate synthetase deficiency; hyperammonemia ii; ornithine transcarbamylase deficiency; hyperammonemia-hyperornithinemia-homocitrullinuria syndrome)

General: Hyperammonemias I a 737g68h nd II are due to errors at or near the 'start' of the urea cycle; in hyperammonemia I, a decrease in the activity of the enzyme carbamyl phosphate synthetase, responsible for the first step of the cycle, results in the accumulation of excess ammonia; in hyperammonemia II, the defect is in ornithine transcarbamylase; type II occurs only in infants.

Ocular: Ptosis and visual loss; retinal depigmentation and chorioretinal thinning.

Clinical: Vomiting; screaming; confusion; lethargy; ataxia; mental retardation; atrophy of cerebral cortex; decreased vibration sense; bucco-faciolingual dyspraxia; learning difficulties; widespread manifestations in the central and peripheral nervous systems.

Evans OB. Hyperammonemia. In: Bradley WG, et al. Neurology in Clinical practice, vol. II, 2nd ed. Boston: Butterworth- Heinemann, 1995:1514-l517.

Fenichel GM. Urea cycle disturbances. In: Fenichel GM, ed. Clinical pediatric neurology; 2nd ed. Philadelphia: WB Saunders, 1993:10-l2.

Harley RD, ed. Pediatric Ophthalmology. 4th ed. Philadelphia: WB Saunders, 1998.

Levin B, et al. Hyperammonaemia: a deficiency of liver ornithine transcarbamylase. Arch Dis Child 1969; 44:152.