| A rare mitochondrial oxidative phosphorylation disorder characterized by a highly variable phenotype which may present as exercise intolerance with prominent exertional dyspnea, progressive muscle weakness, spasticity and neuropathy, but without cognitive impairment or cardiac involvement, or as global developmental delay, growth retardation, hypotonia and spasticity. Hypertrophic cardiomyopathy, optic atrophy, seizures and dysmorphic facial features have also been reported in the more severe phenotype. Serum lactate may be elevated and muscle biopsy shows myopathic features and variably decreased activity of mitochondrial respiratory chain complexes. |
