For instance, single-cell RNA sequencing of postmortem substantia nigra tissue from PD patients revealed cell-type-specific mitochondrial defects: dopaminergic neurons showed marked down-regulation of complex I subunits (NADH: ubiquinone oxidoreductase subunit B3 (NDUFB3), NDUFV1) and reduced expression of PINK1, while astrocytes exhibited impaired fatty acid oxidation-related genes.74, 75, 76 These findings align with earlier clinical observations of multi-complex OXPHOS defects in muscle biopsies from PD patients,77 collectively suggesting systemic mitochondrial dysfunction. This evidence concerns the gene PINK1 and Parkinson disease.