Genetically determined enzyme deficiency causing failure of the lysosomal apparatus is called lysosomal disease. In normal cell the activity of lysosomal enzymes exceeds many times the requirements of the cell. In some individuals due to gene mutation the activity of an intracellular enzyme is only slightly higher than in patients with lysosomal disease but much lower than in the general population, although without evident metabolic and clinical consequences. This situation is called enzyme pseudodeficiency. As yet cases have been reported of the pseudodeficiency of beta-galactocerebrosidase, beta-glucoronidase, beta-glucosidase, beta-hexosoaminidase A and arylosulfatase A. The character of the mutation is called in the case of the two last enzymes and a laboratory method is available for differentiation of pseudodeficiency from the actual lysosomal disease. It is not known whether in pseudodeficiency of an enzyme clinical manifestations could appear in older age.