POLG and progressive external ophthalmoplegia: POLG1-related disorders include a spectrum of overlapping and heterogeneous clinical phenotypes including Alpers syndrome (progressive hepatocerebral degeneration, leading to developmental regression, intractable epilepsy, hepatic failure, and death), the ataxia-neuropathy spectrum, spinocerebellar ataxia with epilepsy, mitochondrial neurogastrointestinal encephalopathy, parkinsonism, and progressive external ophthalmoplegia (PEO) [18].