HBD and Parkinson disease: In the network, genes within these pathways, including HBD, HBB, AHSP, and ALAS2 are connected to SNCA. In this context, it has been demonstrated in experiments with primates that SNCA form a complex with hemoglobin in both brain and blood and that this complex decreases mitochondrial function thus increasing the risk of PD (Yang et al., 2016).