Definition:

Progressive external ophthalmoplegia (PEO) is a a progressive weakness of the external muscles of the eye resulting in blepharoptosis and ophthalmoparesis. Often other muscles are involved resulting in dysphagia and a variable neck and limb muscle weakness. Most sporadic PEO cases have an acquired genetic disease with a heteroplasmic large deletion of mitochondrial DNA (mtDNA) in muscle. In familial PEO, several modes of inheritance occur. Patients may have a nuclear gene defect that predisposes to the accumulation of mtDNA deletions. Recently, mutations in such nuclear genes have been discovered. Some mutations are dominant (PEOA) and others recessive.