Urea cycle disorders

[Renato]

Urea cycle disorders are characterized by hyperammonemia under catabolic or protein-loading conditions.
There are many types of urea cycle and related disorders (see the table) as well as many other amino acid and organic acid metabolism disorders. See also Approach to the Patient With a Suspected Inherited Disorder of Metabolism.
Primary urea cycle disorders (UCDs) include carbamoyl phosphate synthase (CPS) deficiency, ornithine transcarbamylase (OTC) deficiency, argininosuccinate synthetase deficiency (citrullinemia), argininosuccinate lyase deficiency (argininosuccinic aciduria), and arginase deficiency (argininemia). In addition, N-acetylglutamate synthetase (NAGS) deficiency has been reported. The more “proximal” the enzyme deficiency is, the more severe the hyperammonemia; thus, disease severity in descending order is NAGS deficiency, CPS deficiency, OTC deficiency, citrullinemia, argininosuccinic aciduria, and argininemia.
Inheritance for all UCDs is autosomal recessive, except for OTC deficiency, which is X-linked.