POLG and mitochondrial DNA depletion syndrome 4a: Mutations in POLG, the gene that codes for PolγA, are associated with mitochondrial disorders like progressive external ophthalmoplegia (PEO), Alpers–Huttenlocher syndrome (AHS), myocerebrohepatopathy spectrum (MCHS) disorders, myoclonic epilepsy myopathy sensory ataxia (MEMSA), and ataxia neuropathy spectrum (ANS).