The invention provides a composition of glucocerebrosidase, such as velaglucerase alfa, and isofagomine, in a molar ratio of at least about 1 :2.5. Also provided is a use of the composition for treatment of a disorder related to a dysfunction in a GCase pathway. The disorder could be a lysosomal storage disease, such as Gaucher disease, Fabry disease, Pompe disease, a mucopolysaccharidoses, or multiple system atrophy. The disorder could also be a neurodegenerative disorder, such as Parkinson disease, Alzheimer's disease, or Lewy body dementia. The composition can have 0.5 to 5.0 mg/kg of glucocerebrosidase and isofagomine in at least about a 3-fold molar excess to the glucocerebrosidase. The composition can be administered intravenously or subcutaneously.
