Urea cycle disorders: A case report of a successful treatment with liver transplant and a literature review

Table 1 Main causes of urea cycle defects

CPS I deficiency	Genetic defect of carbamoyl phosphate synthetase, inheritated as autosomal recessive mutation
	Block of the first passage of nitrogen in urea cycle
	Neonatal onset when there is a severe enzyme deficiency and adult onset when the effects of mutation are mild
OTC deficiency	X-linked disorder, the most common among UCDs
	Mutation in ornithine transcarbamylase (second passage in urea cycle)
	Clinical presentation very similar to CPS I deficiency
ASS deficiency/citrin deficiency (citrullinemia)	Citrullinemia type I: autosomal recessive defect caused by a deficit of argininosuccinate synthetase, with consequent very high citrulline levels in blood
	Citrullinemia tipe II: caused by a deficit of citrin, a mitochondrial carrier protein of glutamate and aspartate who consequently fail to shuttle to and from the mitochondrion with increase of citrulline levels in blood
ASL deficiency (argininosuccinic aciduria)	Autosomal recessive mutation
	Loss of argininosuccinate lyase with accumulations in body fluids (also in cerebrospinal fluid)
	Seems to lead to mental retardation in all the affected, even when dietary ammonium control is well performed
Arginase deficiency (argininemia)	Arginase I defect
	Peculiar manifestations such as paraplegia and intractable mental retardation
N-acetylglutamate synthetase deficiency	Very rare and clinically overlapped to CPS I deficiency

UCDs: Urea cycle disorders; CPS I: Carbamyl phosphate synthetase 1; ASL: Argininosuccinate lyase; OTC: Ornithine transcarbamylase.