Glucocerebrosidase (GCase) deficiency and the resultant excess brain accumulation of glycosphingolipids, α-synuclein (α-syn) aggregation, proinflammatory cytokine generation, and reactive oxygen species (ROS) production have been linked to PD with both known and unknown causes [20,21,22,23,24,25,26,27,28,29,30,31]. Here, GBA1 is linked to Parkinson disease.