Late-onset encephalopathy associated with a C11777A mutation of mitochondrial DNA.

A 67-year-old man presented with cognitive deficits, status epilepticus, left hemiparesis, and severe lactic acidosis. Respiratory chain enzyme analysis of skeletal muscle revealed a defect in complex I activity, associated with a heteroplasmic C11777A mutation in the mitochondrial ND4 gene. This case is remarkable not only because of the late onset of symptoms, but because this mutation affects the identical ND4 codon as the G11778A mutation that causes Leber hereditary optic neuropathy.