POLG and Parkinson disease: More than 200 mutations in the gene POLG (polymerase gamma), which encodes the catalytic component of mtDNA polymerase, have been implicated in various diseases, including progressive external ophtalmoplegia (PEO), Alper's syndrome (also called Alper-Huttenlocher syndrome), myopathy, parkinsonism (a neurological syndrome characterized by tremor, rigidity and postural instability that shares symptoms found in Parkinson's disease), premature menopause, psychological disorders and ataxia-neuropathy syndrome (http://tools.niehs.nih.gov/polg) (Hudson and Chinnery, 2006; Stumpf and Copeland, 2011).