ADORA2A and Parkinson disease: Based on the association of brain diseases with A2AR up-regulation in afflicted brain regions, several studies explored if A2AR in blood cells could be biomarkers of brain diseases, such as AD (Arosio et al., 2010, 2016; Merighi et al., 2021), PD (Falconi et al., 2019), or ALS (Vincenzi et al., 2013).