The symptoms of mitochondrial myopathies include muscle weakness or exercise intolerance, heart failure or rhythm disturbances, dementia, movement disorders, stroke-like episodes
[ninds.nih.gov]
[…] mitochondrial myopathies include Kearns-Sayre syndrome, myoclonus epilepsy with ragged-red fibers, and mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes
[ninds.nih.gov]
The prognosis for these disorders ranges in severity from progressive weakness to death.
[ninds.nih.gov]