Late-onset Argininosuccinic Aciduria Associated with Hyperammonemia Triggered by Influenza Infection in an Adolescent: A Case Report

Hyperammonemia is a typical symptom of urea cycle disorders. While early-onset argininosuccinic aciduria (ASA) can often be detected by hyperammonemia, patients with late-onset ASA predominantly present with psychomotor retardation and mental disorders. However, in late-onset ASA that develops during early childhood, hyperammonemia can sometimes be caused by acute infections, stress, and reduced dietary intake. Here, we report the case of a 14-year-old boy with late-onset ASA associated with hyperammonemia that was triggered by an influenza A infection. Due to the infection, he presented with a fever and was unable to eat food or take oral medication. He then experienced restlessness, a disturbance in his level of consciousness, and seizures. Hyperammonemia (3286 μg/dL, reference value ≤100 μg/dL) was detected. He was biochemically diagnosed with ASA based on increased serum and urinary argininosuccinic acid levels. Additionally, genetic testing revealed compound heterozygous mutations in the gene: c.91G > A(p.Asp31Asn) and c.1251-1G > C. This case revealed that in late-onset ASA, hyperammonemia can occur not only in early childhood but also during adolescence. Late-onset ASA may have a very broad clinical spectrum that includes hyperammonemia. We suggest that urea cycle disorders such as ASA must be considered when patients present with hyperammonemic decompensation during adolescence.