POLG and External ophthalmoplegia: Mutations in the mitochondrial DNA (mtDNA) polymerase γ (POLG) cause variable neurological presentations such as Alpers–Huttenlocher syndrome (AHS) [6], ataxia neuropathy spectrum including the phenotypes previously referred to as mitochondrial recessive ataxia syndrome (MIRAS), sensory ataxia, neuropathy, dysarthria, ophthalmoplegia (SANDO) [7] and chronic progressive external ophthalmoplegia (CPEO) plus parkinsonism [8].