GCH1 and Dystonia: In the present review, we will focus on advances in the research on the synaptic function in dystonia obtained from experimental models of the most extensively studied forms of isolated dystonia: DYT-TOR1A (generalized early-onset dystonia); DYT-THAP1 (craniocervical and limb dystonia); DYT-GNAL (adult-onset craniocervical dystonia), and of combined dystonia: DYT/PARK-GCH1 and DYT/PARK-TH (dopa-responsive dystonia, DRD), and DYT-SGCE (myoclonus-dystonia).