Table 3.
Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) Patients with histological, biochemical, and/or molecular evidence of mitochondrial disease who experience stroke-like episodes. Specifically associated features (at least in MELAS due to the m.3243A>G mutation) include lactic acidosis, generalized seizures, cognitive involvement, and hearing loss. |
Myoclonic encephalomyopathy with ragged red fibers (MERRF) A mitochondrial syndrome where myoclonus is the prominent clinical feature, and which does not meet the criteria of other well-defined mitochondrial encephalopathic syndromes, including MELAS, Leigh, and Alpers syndromes. Ataxia is a specifically associated feature, differently from epileptic seizures. |
Kearns-Sayre Syndrome (KSS) spectrum Ophthalmoparesis and/or ptosis due to a mtDNA single large-scale deletion and at least one of the following features:
|
Progressive external ophthalmoplegia (PEO) Ophthalmoparesis and/or ptosis, not fulfilling the criteria for Pearson syndrome nor “KSS spectrum” criteria or other encephalopathic syndromes. “Pure PEO”: isolated ocular myopathy. “PEO plus”: ocular myopathy with other features of neuromuscular involvement. |
Primary mitochondrial myopathies (PMM) Genetically defined disorders leading to defects in oxidative phosphorylation affecting predominantly skeletal muscles (not fulfilling the criteria for other more complex syndromes). |