Similarly, the peroxisome proliferator-activated receptor γ coactivator 1 alpha (PGC-1α) has been of interest due to its role as a regulator of mitochondrial function.228 The PGC-1α reference gene and PGC-1α levels are downregulated in human brain and blood leucocytes in PD compared with control patients, and this negatively correlates with disease severity.229–231 Interventions targeting mitochondrial processes might usefully measure peripheral levels of PGC-1α. This evidence concerns the gene PPARGC1A and Parkinson disease.