POLG and mitochondrial DNA depletion syndrome 4a: Diseases associated with Polγ dysfunction caused by mutations in the POLG gene include mitochondrial DNA depletion syndrome 4A (Alpers type, MIM 203700), a fatal infant disease with epilepsy and drug induced liver failure, mitochondrial DNA depletion syndrome 4B (MNGIE type, MIM 613662) with gastrointestinal involvement, mitochondrial recessive ataxia syndrome (includes SANDO and SCAE, MIM 607459), and relatively benign progressive external ophthalmoplegia autosomal dominant 1 (MIM 157640) and autosomal recessive 1 (MIM 258450) (Naïmi et al. 2006).