Overall, despite the presence of pyrimidine signaling molecules acting on the P2Y2, 4, 6, 14 receptor subtypes (von Kügelgen and Hoffmann, 2016) and on the P2Y-like receptor GPR17 (see section Involvement of the Purinergic System in Brain Alterations Observed in Down Syndrome), this system is referred to as the “purinergic system” (Burnstock, 2017). This evidence concerns the gene P2RY2 and Down syndrome.