ALDH1A1 and Parkinson disease: Several studies in PD patient brains revealed a decreased expression and activity of the catabolic enzyme aldehyde dehydrogenase 1A1 (ALDH1A1) [7, 8], which is responsible for the degradation of the dopamine intermediate 3,4-dihydroxyphenylacetaldehyde (DOPAL) generated by monoamine oxidase (MAO).