Sialidase-1 belongs to the N-acetyl-a neuraminidase family. Sialidase-1 is expressed in many tissues; it is highly expressed in the pancreas, and weakly expressed in the brain. Sialidase-1 is a lysosomal enzyme, which cleaves terminal sialic acid residues from substrates such as glycoproteins and glycolipids. Deficiencies in the human enzyme Sialidase-1 leads to sialidosis, a rare lysosomal storage disease. Sialidase-1 has been shown to interact with Cathepsin A (protective protein), β-galactosidase and N-acetylgalactosamine-6-sulfate sulfatase in a multienzyme complex.