Thus, reduced D2 pre-synaptic inhibitory action further supports hyperdopaminergia in MPS-IIIA mice, which results in over-stimulation of the D1-direct pathway, as evidenced by increased phosphorylation of its downstream target, the DA and cAMP-regulated phosphoprotein of relative molecular mass 32,000 (p-DARPP-32). The gene discussed is PPP1R1B; the disease is mucopolysaccharidosis.