In addition, gene therapy based on transfection of mtDNA-complexed TFAM or recombinant TFAM to PD cybrid cells shows potential to restore mitochondrial bioenergetics of severely impaired nigral neurons, as TFAM is important for mtDNA maintenance (Keeney et al., 2009; Golpich et al., 2017). This evidence concerns the gene TFAM and Parkinson disease.