This research focuses on the activity of an enzymatic protein: glucocerebrosidase, in dementia with lewy bodies (DLB). Indeed, the mutation of the GBA gene responsible for a decrease in the activity of glucocerebrosidase is the most frequent known genetic risk factor in DLB. However, mutations of the GBA gene are known in another pathology, Gaucher disease, in which treatments have been developed. The objective of this research is to determine if glucocerebrosidase activity is decreased in DLB. This hypothesis could open up a therapeutic perspective, with treatments already used in Gaucher disease.