The present invention provides composition and methods for diagnosis and treatment of lysosomal storage diseases and their diagnosis and treatment, including Gaucher's Disease and Tay-Sachs disease, and particularly which utilize progranulin (PGRN), or active PGRN peptides, including atsttrin. The invention also provides animal models of lysosomal storage diseases, including Gaucher's Disease and Tay-Sachs disease, based on or including PGRN mutations including PGRN null mutants and PGRN gene knock outs.