One of the most commonly mutated genes in PD patients is the beta-glycosylceramidase (GBA) gene encoding a lysosomal enzyme, glucocerebrosidase (GCase—D-glucosyl-N-acylsphingosine glucohydrolase), which conducts the hydrolysis of glucocerebrosides (by the removal of glucose moiety). Here, GBA1 is linked to Parkinson disease.