Leber's hereditary optic neuropathy mutations associated with infantile-onset myoclonic epilepsy.

Epilepsy syndromes with onset in the first year of life, especially when they include myoclonic features, have special significance since they are associated with long-term developmental and neurological abnormalities. Dravet's severe myoclonic epilepsy in infancy is especially interesting as it is associated with fever-provoked seizures and mutations in the alpha subunit of the sodium channel (SCN1A) in about one-third of the cases. Here, we report 2 children who had clinical features of severe myoclonic epilepsy of infancy without mutations in the SCN1A gene who were found to have mitochondrial DNA mutations associated with Leber's hereditary optic neuropathy. These 2 children demonstrated markers of mitochondrial dysfunction, drug-resistant epilepsy, and dysfunction of nonneurological systems. These cases demonstrate that mitochondrial DNA mutations, especially those associated with Leber's hereditary optic neuropathy, should be considered in cases of myclonic epilepsy starting in infancy, especially when mutations in the SCN1A gene are not found.