The signs and symptoms of mitochondrial complex III deficiency are not the same for each affected individual, because a person with mitochondrial disease
can have a unique mixture of healthy and defective mitochondria
, with a unique distribution in the body.
Several forms of mitochondrial complex III deficiency have been identified, and they are generally grouped based on the age of onset, nature and severity of symptoms.
The most severe form begins in infancy and causes life-threatening muscle and nervous system dysfunction (encephalomyopathy), lactic acidosis
at birth, hypotonia
(poor muscle tone), dystrophic posturing, seizures
, and coma. Ragged-red fibers, a characteristic microscopic abnormality observed in muscle biopsy
, are commonly present with this form.
In some individuals, encephalomyopathy does not begin until childhood or adulthood. For these individuals, symptoms may include various combinations of weakness, short stature
(inability to coordinate muscle movements), dementia
, hearing loss
, sensory neuropathy, pigmentary retinopathy (a disorder of the retina characterized by deposits of pigment and vision loss), and possible lactic acidosis or other features. Ragged-red fibers are common in these individuals as well.
Individuals with a less severe type may have myopathy
with exercise intolerance that progresses to general weakness. Ragged-red fibers and lactic acidosis may be present.
A fourth described form is characterized by infantile histiocytoid cardiomyopathy. This is a condition characterized by cardiomegaly (enlarged heart), severe cardiac arrhythmias or sudden death, and the presence of histiocyte-like cells within the heart muscle.
Last updated: 8/29/2011
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