Mutations of TWNK are well-described in mitochondrial DNA depletion syndrome 7 (MTDPS7) which is also known as infantile-onset spinocerebellar ataxia (infantile onset-SCA) [13] and autosomal dominant progressive external ophthalmoplegia 3 (autosomal dominant-PEO3) [6]. The gene discussed is TWNK; the disease is mitochondrial DNA depletion syndrome 7 (hepatocerebral type).