Despite intracellular localization of endogenous CDNF, in vivo data with intracerebral injections of recombinant human CDNF shows that it can protect dopamine neurons, and more importantly, restore the functionality of the nigrostriatal dopamine system after toxin-induced degeneration in rodent models of Parkinson’s disease (PD) (Lindholm et al., 2007; Voutilainen et al., 2011; Airavaara et al., 2012). This evidence concerns the gene CDNF and Parkinson disease.