A significant risk association was found with variants of Human Leukocyte Antigen–Major Histocompatibility Complex II (HLA–MHC II) genes (Hamza et al., 2010; Pierce and Coetzee, 2017), Nitric Oxide Synthase 1 and 2a (NOS1 and NOS2A) genes (coding for neuronal and inducible isoforms of NOS, respectively (Hancock et al., 2008), Tumor Necrosis Factor-α (TNF-α) and its Receptor 1 (TNFR1) genes (coding for the proinflammatory cytokine and its receptor; Krüger et al., 2000), suggesting a role of neuroinflammation in PD etiology (Tansey et al., 2007; Hirsch and Hunot, 2009; Johnson et al., 2019). Here, NOS2 is linked to Parkinson disease.