MT-ND6 and supranuclear palsy, progressive, 1: Cytochrome-b is a vital component of complex III and ND6 is a subunit of complex I. Both complex I and III are important components of the OXPHOS pathway, and have been identified as major drivers of neurodegeneration and dysfunction of complex I has also been shown to accelerate 4R tau isoform formation in PSP cell lines [26, 27].