POLG and mitochondrial DNA depletion syndrome 4a: For example, the homozygous mutation in POLγA p.A467T has been observed in patients with AHS (Alpers-Huttenlocher syndrome), MELAS, MEMSA (Myoclonic Epilepsy, Myopathy, and Sensory Ataxia), and SANDO (sensory ataxia neuropathy dysarthria and ophthalmoplegia), accompanied by a profound mtDNA depletion or deletions (Neeve et al., 2012; Rajakulendran et al., 2016).