Multiple defects of the respiratory chain including complex II in a family with myopathy and encephalopathy.

We report severe deficiency of complex II of the mitochondrial respiratory chain and low activities of complex I and II in skeletal muscle mitochondria from a young woman with progressive muscle weakness and encephalopathy. Defects of complex II have only very rarely been described and this is the first report of decreased immunoreactive subunits associated with severe deficiency of this enzyme.