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HomePediatrics: Genetics and Metabolic DiseaseArgininosuccinate Lyase (ASL) Deficiency

Argininosuccinate Lyase (ASL) Deficiency


Argininosuccinate (ASA) lyase deficiency results in defective cleavage of ASA. This leads to an accumulation of ASA in cells and an excessive excretion of ASA in urine. In virtually all respects, this disorder shares the characteristics of other urea cycle defects.
The most important characteristic of ASA lyase deficiency is its propensity to cause hyperammonemia in affected individuals. See the image below.

Compounds comprising the urea cycle are numbered s

Compounds comprising the urea cycle are numbered sequentially, beginning with carbamyl phosphate (1). At this step, the first waste nitrogen is incorporated into the cycle; at this step, N-acetylglutamate exerts its regulatory control on the mediating enzyme, carbamyl phosphate synthetase (CPS). Compound 2 is citrulline, the product of condensation between carbamyl phosphate (1) and ornithine (8); the mediating enzyme is ornithine transcarbamylase. Compound 3 is aspartic acid, which is combined with citrulline to form argininosuccinic acid (ASA) (4); the reaction is mediated by ASA synthetase. Compound 5 is fumaric acid generated in the reaction that converts ASA to arginine (6), which is mediated by ASA lyase.

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