Genome wide association studies (GWAS) identified over 40 PD risk loci, the majority of which overlaps with known autosomal dominant PD genes, most notably SNCA and LRRK2, while other studies revealed the presence of heterozygous variants in autosomal recessively inherited PD genes (Simón-Sánchez et al., 2009; Nalls et al., 2014; Zeng et al., 2018; Germer et al., 2019; Lai et al., 2020). This evidence concerns the gene SNCA and Parkinson disease.