external ophthalmoplegia; progressive external ophthalmoplegia (PEO)
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Pathology
- ragged-red fibers (RRFs) with focal cytochrome c oxidase deficiency in skeletal muscle
Genetics
- autosomal dominant progressive external ophthalmoplegia
- mutations in the twinkle gene
- defects in SLC25A4 (mitochondrial DNA deletions 2)
- defects in POLG (mitochondrial DNA breakage syndrome)
- defects in POLG2 (mitochondrial DNA deletions 4) multiple mitochondrial DNA deletions in skeletal muscle
- autosomal recessive progressive external ophthalmoplegia with mitochondrial DNA deletions
Clinical manifestations
- adult onset of ptosis & weakness of the extraocular muscles & exercise intolerance (autosomal dominant form)
- progressive weakness of ocular muscles & levator palpebrae superioris
- in a minority of cases, it is associated with skeletal myopathy predominantly involving axial or proximal muscles resulting in abnormal fatigability & even permanent muscle weakness
- additional symptoms are variable, & may include cataracts, hearing loss, sensory axonal neuropathy, ataxia, depression, hypogonadism, & parkinsonism
- autosomal recessive form is often associated with multisystemic disorders, is clinically more heterogeneous than the autosomal dominant form & can be more severe