Mitochondrial myopathy is generic name encompassing a group of neuromuscular diseases caused by pathologic dysfunction of the mitochondrial respiratory chain. Since neurons and muscle cells require a great deal of energy, they are affected the most in such cases of mitochondrial dysfunction. Myopathy may be the only or main symptom, or it can be associated with a multisystemic illness.

Diagnosis is made upon clinical and neurological manifestations such as progressive muscle fatigability, muscle weakness, hypotonia and hyporeflexia. Additionally, laboratory tests can reveal unusually large mitochondria with increased oxidative enzymes and neutral fat on muscle biopsy. On the other hand, muscle mitochondria appear to harbor anomalous quadrilaminar structures. Treatment is mainly supportive and prognosis varies widely according to each specific case.

Mitochondrial myopathy disorders result from mutations in the mitochondrial DNA (mtDNA). These mutations can lead to defects in substrate utilization, uncoupling mitochondrial respiration to phosphorylation or deficiencies in components of mitochondrial respiratory chain. Due to the wide variation in the molecular etiology of these cases no general pattern of inheritance could be deduced.