Citrullinemia type 2
Citrullinemia is one of the urea cycle disorders, caused by argininosuccinic acid synthetase deficiency (ASS), with an estimated incidence of 1/57,000 live births. The diagnosis of citrullinemia is based on biochemical analysis of blood, plasma, and urine, revealing increased levels of ammonia, citrulline, glutamine, and orotic acid. ASS enzyme activity can be assayed in liver samples and cultured fibroblasts. In neonatal-onset disease, neonates exhibit lethargy and vomiting 24–72 hours after birth, rapidly progressing to respiratory insufficiency and coma. Neurodevelopmental outcome of neonatal urea cycle defects is disappointing and is related to the duration of neonatal hyperammonemic coma. There is, however, no consensus regarding other early prognostic indicators. Reports on imaging findings in citrullinemia are sparse. A recent article describes CT findings in two infants in the chronic stage of this disease.
Type 2 citrullinemia is also an adult-onset, autosomal recessive disorder characterized by episodes of hyperammonemic encephalopathy. It is caused by mutations in the SLC25A13 gene, which encodes the liver-specific isoform of the mitochondrial aspartate–glutamate carrier (AGC2).
