MedGen

Infantile mitochondrial myopathy due to reversible COX deficiency is a rare mitochondrial disorder characterized by onset in infancy of severe hypotonia and generalized muscle weakness associated with lactic acidosis, but is distinguished from other mitochondrial disorders in that affected individuals recover spontaneously after 1 year of age (summary by Mimaki et al., 2010). See also transient infantile liver failure (LFIT; 613070), which is a similar disorder. [from OMIM]

The presence of an increased amount of muscle fibers with an increased diameter. This feature can be ascertained by microscopic examination of a muscle biopsy sample. Together with fiber size variation and atrophied muscle fibers, and hypertrophied muscle fibers are commonly found in myopathies. [from HPO]