POLG and autosomal dominant progressive external ophthalmoplegia: POLG1-related PEO can occur in either autosomal recessive (arPEO) form, characterized by ptosis and ophthalmoparesis, or autosomal dominant (adPEO) form that can include symptoms of myopathy, hearing loss, cataracts, ovarian failure, axonal neuropathy, ataxia, depression and parkinsonism [55].