One priority in cell replacement therapy for Neurodegenerative disorders (NDDs) has been Parkinson’s disease (PD), where hESCs have successfully generated electrophysiologically active midbrain dopamine neurons through the strategic and systematic application of signaling molecules Fibroblast Growth Factor 8 (FGF-8) and Sonic Hedgehog (Shh), playing prerequisite roles in development and differentiation of various tissues in the nervous system (Guillaume and Zhang, 2008). Here, SHH is linked to Parkinson disease.