Clinical features:
Onset before 20 years of age. Progressive external opthalmoplegia (restricted eye movements, usually movements are not dysconjugated) and pigmentory retinopathy. Also myopathy, heart block, CNS deficits, short stature.
Pathology:
Muscle biopsy:
Gomori trichrome: Ragged red fibres
Variation in muscle size
COX negative fibres
Brainstem and cerebellum:
neuronal loss. Spongy to vacuolar myelinopathy. May extend to cerebral white matter.
Basal ganglia and thalamus: may mineralize
Genetics:
mitochondrial DNA (mtDNA) deletions