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). Here, HBB is linked to Parkinson disease.