ALDH1A1 and Parkinson disease: Besides in the substantia nigra of PD patients (Galter et al., 2003; Grunblatt et al., 2004; Werner et al., 2008), the mRNA expression of ALDH1A1 is also shown to be reduced in the peripheral blood of sporadic PD patients, and the gene is classified as an optimal predictor for PD risk in a panel with four other genes (Molochnikov et al., 2012).