This increase in turning with fewer DARPP32 neurons and fewer DARPP32 striato‐GPe fibers reflects a hyperkinesia that would be expected from iSPN dysfunction or loss, based on the standard direct–indirect pathway model of basal ganglia function (Albin et al., 1989; DeLong, 1990; Reiner et al., 1988). This evidence concerns the gene PPP1R1B and Hyperkinetic movements.