Epileptic phenotypes associated with mitochondrial disorders

Objective: To define the clinical and EEG features of the epileptic syndrom es occurring in adult and infantile mitochondrial encephalopathies (ME). Me thods: Thirty-one patients with recurrent and apparently unprovoked seizure s associated with primary ME were included in the study. Diagnosis of ME wa s based on the recognition of a morphologic, biochemical, or molecular defe ct. Results: Epileptic seizures were the first recognized symptom in 53% of the patients. Many adults (43%) and most infants (70%) had nontypical ME p henotypes. Partial seizures, mainly with elementary motor symptoms, and foc al or multifocal EEG epileptiform activities characterized the epileptic pr esentation in 71% of the patients. Generalized myoclonic seizures were an e arly and consistent symptom only in the five patients with an A8344G mitoch ondrial DNA point mutation with classic myoclonus epilepsy with ragged red fibers (MERRF) syndrome or "overlapping" characteristics. Photoparoxysmal E EG responses were observed not only in patients with typical MERRF, but als o in adult patients with ME with lactic acidosis and strokelike episodes (M ELAS), or overlapping phenotypes, and in one child with Leigh syndrome. Con clusions: Epilepsy is an important sign in the early presentation of ME and may be the most apparent neurologic sign of nontypical ME, often leading t o the diagnostic workup. Except for those with an A8344G mitochondrial DNA point mutation, most of our patients had partial seizures or EEG signs indi cating a focal origin.