A familial mitochondrial myopathy with central defect in neural transmission.

A family was found to exhibit progressive external ophthalmoplegia, congenital cataracts, variable somatic weakness, gonadal dysgenesis, and, in one member, an abnormal chromosomal pattern. Muscle biopsy specimens showed "ragged-red" fibers; electron microscopy showed widespread paracrystalline mitochondrial inclusions. Orbicularis oculi reflex testing in the propositus showed bilateral absence of the late response. The family was evaluated in relation to other familial mitochondrial myopathies; a central defect in brain stem neural transmission was suggested as a mechanism for the progressive external ophthalmoplegia.