Sialidases have important roles in the degradation of glycoconjugates by removing terminal sialic acid residues.
Defects in sialidase 1 (NEU1) cause sialidosis, a lysosomal storage disease characterised by the progressive lysosomal storage of sialidated glycopeptides and oligosaccharides and the accumulation and excretion of N-acetylneuraminic acid (Neu5Ac) covalently-linked ('bound') glycoconjugates (Lowden & O'Brien 1979). The sialidoses are distinct from the sialurias in which there is storage and excretion of 'free' Neu5Ac. Sialidosis manifests into types I and II forms. Type I is the milder form, also known as the 'normosomatic' type or the cherry red spot-myoclonus syndrome. Sialidosis type II is the more severe form with an earlier onset, and is also known as the 'dysmorphic' type.