POLG and Parkinson disease: To date more than 200 mutations have been reported in the POLG gene (see http://tools.niehs.nih.gov/polg/) and they are correlated with a variety of mitochondrial disorders, including Alpers syndrome, progressive external ophthalmoplegia (PEO), Parkinsonism, and other encephalomyopathies associated with mtDNA mutations, deletions, and depletions (Stumpf and Copeland, 2011).