Onset typically is during the neonatal period.
Main features include failure to thrive, signs of hyperammonemia (anorexia,
irritability, tachypnea, lethargy, vomiting), and additional neurologic
signs (progressive spastic quadriplegia, seizures, mental retardation,
hyperactivity). Coma and cerebral edema may occur. Usually mild hepatomegaly
can occur. Laboratory findings include hyperammonemia, hyperarginemia,
di-amino-aciduria (arginuria, lysinuria, cystinuria, ornithinuria),
oroticaciduria, pyrimidinuria, and elevated amino acid levels in the
cerebrospinal fluid (arginine, ornithine, aspartate, threonine, glycine,
methionine). Stress and infection can trigger an attack.