COMT and Parkinson disease: In fact, according to our analysis, genes reported as playing a role in PD [ABL1 (Mahul-Mellier et al., 2014), COMT (Jiménez-Jiménez et al., 2014), GRK5 (Liu et al., 2010), and APT1A3 (Haq et al., 2019)] were found associated with neuronal loss rather than the disease itself (Figures 5A,C).