DRD1 and Parkinson disease: In examining the integrated mechanism network three routes emerged for triggering the Parkinson's disease mechanism via one of the extra-cellular ligands CX3CL1, IL12B and SEMA6D. In the first route, CX3CL1 (fractalkine) together with DRD1 (dopamine receptor D1) suppresses the expression of ionotropic glutamate receptor GRIA1. There is also interaction between CX3CL1, ADAM17 (metallopeptidase domain 17), and LCAM1 which then follows a downstream path into cytoplasm and to the nucleus for subsequent regulation of gene expression.