Parkinson disease (PD) is pathologically defined by (i) the loss of dopaminergic neurons in the substantia nigra (SN) and (ii) the prevalence of proteinaceous Lewy bodies, mainly composed of SNCA/α‐synuclein (synuclein alpha) and other polyubiquitinated proteins but also vesicular structures. This evidence concerns the gene SNCA and Parkinson disease.