A 4-year-old boy with developmental delay presents with self-injurious behavior, repeatedly striking his head against walls and severely biting his fingertips requiring bandaging. Vital signs: BP 95/60, HR 98, RR 20, Temp 37°C, SpO2 98%. Serum uric acid is elevated at 9.2 mg/dL. He denies recent fever or joint pain. His parents report normal birth history. Elevated blood levels of which of the following would be most diagnostic of this disorder?

1. A)Uric acidGABARITO
2. B)Dicarboxylic acids
3. C)Ammonium ion
4. D)Orotic acid
5. E)Phenylacetate