MCAT and cerebellar ataxia: Interestingly, a single PwMS had a pathogenic variant, namely, m.11778G > A in the MT-ND4 gene, which is associated with Leber’s hereditary optic neuropathy (LHON) and neuropathy, ataxia, and retinitis pigmentosa (NARP), albeit at low VLs: 5.8% and 7.3% for VIS1 and VIS2, respectively; well below the VLs usually required for pathogenesis36.