KCND2 and Parkinson disease: Both “cAMP” and “calcium” exerted strong direct and indirect effects on the glutamate metabotropic receptor 5 “Grm5_Interaction.” Genes upstream (Lrrc7) and downstream (Kcnd2) of the glutamate metabotropic receptor 5 (Grm5), as well as Grm5 itself, were downregulated in the PD Signature.