These metabolic processes require the action of carbamoyl phosphate synthetase (CPS) isozymes with different subcellular localization. ![]() The first participates in the synthesis of urea, and the second in the synthesis of pyrimidine. In cells, particularly hepatocytes, there are two separate pools of carbamoyl phosphate, one is in mitochondria and the other in the cytosol. However, there are important differences between them. The reaction is similar to the first step of the urea cycle. Management is symptomatic and supportive because there is no definitive or curative treatment. Treatment with D-ribose and uridine supplementation has been shown to be of limited benefit. Affected infants may have disturbed glucose and lipid metabolism as a result of impaired hepatic gluconeogenesis and fatty acid and cholesterol synthesis. The cardinal biochemical feature is elevated riboside metabolites 5-amino-4-imidazolecarboxamide ribosiduria (AICA) and succinyl-5-amino-4-imidazolecarboxamide ribosiduria (SAICA) in urine and CSF. These infants develop severe static encephalopathy with profound mental retardation, blindness as a result of optic atrophy, refractory epilepsy, and growth failure. Neuroimaging may be normal initially, followed later by diffuse atrophy. ![]() ![]() Affected infants are born uneventfully at term and develop severe neonatal encephalopathy with hypotonia and seizures. Purine biosynthesis disorders manifesting in the neonatal period involve adenylosuccinate lyase or riboside transformylase enzyme deficiencies ( Jurecka, 2009). Bearden, in Swaiman's Pediatric Neurology (Sixth Edition), 2017 Purine Biosynthesis Defects
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