ADORA2A and Vasovagal syncope: Regarding NCS, a classification based on adenosinergic profiling was recently proposed [53]: The syncope with prodromes (vasovagal syncope) is associated with high APL and high A2AR expression on PBMC, a specific single-nucleotide polymorphism in A2AR gene, and a positive head-up tilt test [56], while the sudden syncope without prodromes is associated with low APL levels and low A2AR expression [53,54,55].