Table Some Mitochondrial Disorders Disorder Description Chronic progressive external ophthalmoplegia (CPEO) Progressive paralysis of the extraocular muscles usually preceded by bilateral, symmetric, progressive ptosis that begins months to years earlier Kearns-Sayre syndrome A multisystem variant of chronic progressive external ophthalmoplegia that also includes heart block, retinitis pigmentosa, and central nervous system degeneration Leber hereditary optic neuropathy Variable but often devastating bilateral vision loss that often occurs in adolescents and that is due to a point mutation in mitochondrial DNA Myoclonic epilepsy with ragged-red fibers (MERRF) syndrome Progressive myoclonus and seizures, dementia, ataxia, and myopathy Mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes (MELAS) syndrome MELAS episodes Pearson syndrome Sideroblastic anemia, pancreatic insufficiency, and progressive liver disease that begins in the first few months of life and is frequently fatal in infants Maternal inheritance patterns characterize abnormalities of mitochondrial DNA.