The MAN2B1 gene maps to chromosome 19p13.2, where it gives instructions for making an enzyme called alpha-mannosidase. This protein is made up of 1011 amino acids; and weighs about 114 kDa. Alpha-mannosidase is a lysosomal enzyme that hydrolyzes terminal, non-reducing alpha-D-mannose residues in alpha-D-mannosides. This activity is necessary for the catabolism of N-linked carbohydrates released during glycoprotein turnover.

Defects in this enzyme are the cause of Alpha-Mannosidosis, a lysosomal storage disease characterized by accumulation of unbranched oligosaccharide chains. The symptoms of this disease range widely in their onset and severity, and may include distinctive facial features, skeletal abnormalities, hearing loss, intellectual disability, and dysfunction of the immune system.