GSTM1 and Parkinson disease: Hb has also been shown to regulate genes involved in oxygen homeostasis and oxidative phosphorylation, linking Hb expression to mitochondrial activity.10 Hb overexpression in mouse dopaminergic cell lines upregulates the expression of genes involved in mitochondrial oxidative phosphorylation.11 Conversely, administration of rotenone (a well-known complex I inhibitor) downregulates Hb α- and β-chain expression in rat nigral, striatal, and cortical neurons.11 We suggest that a reduction in neuronal Hb in PD patients could contribute to an imbalance in mitochondrial homeostasis and hypoxia.