Since MANF and CDNF promote the survival of brain dopamine neurons in animal models of PD (Lindholm et al., 2007; Voutilainen et al., 2009; Airavaara et al., 2012; Back et al., 2013; Ren et al., 2013; Garea-Rodriguez et al., 2016; Hao et al., 2017; Liu et al., 2018), we wanted to study whether their endogenous levels are altered in human subjects with PD, which would indicate a possible contribution to the disease mechanism. The gene discussed is CDNF; the disease is Parkinson disease.