Mitochondrial cytopathy presenting as hereditary sensory neuropathy with progressive external ophthalmoplegia, ataxia and fatal myoclonic epileptic status.

We present six adult patients from three separate families, with a remarkably uniform heredo-ataxic syndrome, developing in three stages and ending in early death. The initial stage is determined by severe sensory neuropathy. The second stage is characterized further by progressive external ophthalmoplegia (PEO), probably caused by ocular myopathy, and progressive ataxia. During a short last stage there is epilepsia, and particularly myoclonic status epilepticus, of which four patients died unexpectedly. Sural nerve biopsies showed severe loss of myelinated fibres in a rather early stage of disease. Skeletal muscle biopsies (and a specimen of ocular muscle) revealed ragged-red fibres. Autopsy examination in two patients revealed multisystemic involvement of the nervous system, with, in particular, degeneration of spinal dorsal columns and spinocerebellar tracts. Pedigree data were compatible with an autosomal recessive disorder. Additional findings, particularly elevation of CSF lactate, suggested mitochondrial cytopathy as an essential feature of the multisystem degeneration in these patients.