MT-ATP6 and NARP syndrome: The neuropathy, ataxia, retinitis pigmentosa (NARP) syndrome is caused by heteroplasmic pathogenic variants in MT-ATP6 in mitochondrial DNA (mtDNA) that encodes subunit 6 of mitochondrial H+-ATPase or mitochondrial OXPHOS Complex V. Six variants have been reported in MT-ATP6 in patients with NARP: m.8993T > G (p.Leu156Arg), m.8993T > C (p.Leu156Pro), m.8839G > C (p.Ala105Pro), m.8989G > C (p.Ala155Pro), m.8618insT (p.Thr33Hisfs*31), and m.9185T > C (p.Leu220Pro)9.