PPARGC1A and Parkinson disease: Recent studies have also found that the crucial transcription factors PGC1-α (peroxisome proliferator-activated receptor-gamma coactivator-1 alpha) and TFAM (transcription factor A, mitochondrial), which regulate mitochondrial biogenesis, are down-regulated in PD patients,14,15 providing evidence of impaired mitochondrial biogenesis in PD.