Regarding the nigrostriatal pathway, which is especially affected in PD, it was demonstrated that through maturation, mice lacking either FGF-2LMW or FGF-2HMW develop more DA neurons within the substantia nigra (SN) pars compacta, equally distributed to the hyperplasia phenotype previously described for adult mice lacking FGF-2 [99]. The gene discussed is FGF2; the disease is Parkinson disease.