SNCA and Parkinson disease: Variants of some genes, including the synuclein alpha gene (SNCA), LINGO1, LINGO2, HTRA2, the leucine‐rich repeat kinase 2 gene (LRRK2), and the DnaJ heat‐shock protein family (Hsp40) member C13 gene (DNAJC13), have been shown to exert either a risk or protective effect on ET and PD, or to be responsible for both disorders (Chao et al., 2015; Tio & Tan, 2016; Unal Gulsuner et al., 2014).