POLG and mitochondrial DNA depletion syndrome 4a: POLG-SDs caused by mutations in POLG are usually autosomal recessive and range from Alpers–Huttenlocher syndrome (AHS, fatal progression usually within weeks to a few years after birth), ataxia neuropathy spectrum (ANS), and myoclonic epilepsy myopathy sensory ataxia (MEMSA) to often late-onset progressive external ophthalmoplegia (PEO) [2], [3].