An 8-year-old female child with congenital ornithine transcarbamylase deficiency (OTCD) who presented with a hyperkinetic behavior disorder at 3 years is reported from the Medical School Hanover, Germany. Methylphenidate therapy was used for 1 year without benefit. At age 6, she developed increasing somnolence, hypotonia and dyskinesia during high fever. The diagnosis of OTCD was based on hyperammonemia, increased glutamine, low normal citrulline and decreased arginine in the blood, and elevated orotic acid and uracil in urine. Mutation analysis of the OTC gene revealed heterozygosity for 274C; R92X. Despite therapy with a low protein diet, glucose, arginine, benzoate and phenylbutyrate, she became comatose for a week before slowly waking with flapping tremor and seizures. MRI showed cerebellar atrophy and white matter lesions. One year after the metabolic stroke, metabolic control and clinical improvement were observed. 
COMMENT. In a young child with hyperkinetic behavior unresponsive to methylphenidate, a metabolic cause should be considered in the differential diagnosis.