Thus, in the two patients with a homoplasmic mutation in the mtDNA gene MT-ATP6 (P14 and P15), the highest sNFL levels were detected in P15, with ataxia, dysarthria, epilepsy, optic atrophy, cognitive impairment and polyneuropathy as compared to P14 with polyneuropathy. Here, MT-ATP6 is linked to hereditary optic atrophy.