Activation of Shh signaling through the injection of active Shh protein in rodent or primate models of Parkinson’s disease has been shown to preserve TH immunoreactive neurons in the SN and dopaminergic axons in the striatum, improving motor function (Dass et al. 2002; Tsuboi and Shults 2002; Dass et al. 2005). Here, SHH is linked to Parkinson disease.