POLG and progressive external ophthalmoplegia: Moreover, polymerase gamma (POLG) is an enzyme responsible for the replication and repair of mitochondrial DNA (Chan & Copeland, 2009) and mutation in the POLG may cause various clinical manifestations, including parkinsonism (Miguel et al., 2014), epilepsy (Stricker et al., 2009; Stumpf, Saneto, & Copeland, 2013), cerebellar ataxia (Stricker et al., 2009; Stumpf et al., 2013), and progressive external ophthalmoplegia (Luoma et al., 2004; Miguel et al., 2014).