GBA1 and Parkinson disease: Genetic forms of PD represent 5–10% of all cases including mutations in the GBA gene that encodes glucocerebrosidase and accounts for 5–15% of PD patients, as well as mutations in the LRRK2 gene encoding for leucine-rich repeat kinase 2, the SNCA gene for αsyn, and the PRKN and PINK1 genes for parkin and pink.