Lysosomal alpha-mannosidase (LAMAN), in the following called mannosidase, is an enzyme that cleaves alpha-mannosidic linkages during the ordered degradation of oligosaccharides. Only after degradation, can the sugars leave the lysosomes, the cell and later the body. The deficiency in mannosidase activity causes a block in the degradation of glycoproteins resulting in lysosomal accumulation of mannose-rich oligosaccharide chains. Consequently, these sugars accumulate in the lysosomes as they are too large to leave. Finally, the lysosomes increase in size, producing vacuoles and impaired cellular function is induced by an unknown mechanism.