Wikipedia says
Mitochondrial myopathy, Encephalopathy, Lactic Acidosis, Stroke-like episodes. MELAS is one of the family of mitochondrial cytopathies, which also include MERRF, and Leber's Hereditary Optic Atrophy. A feature of these diseases is that they are caused by defects in the mitochondrial genome which is inherited purely from the female parent. The disease can manifest in both sexes.

http://en.wikipedia.org/wiki/MELAS