A defect in exodegradative pathways provides insight into endodegradation of heparan and dermatan sulfates.

Within cells, dermatan sulfate (DS) and heparan sulfate (HS) are degraded in two steps. The initial endohydrolysis of these polysaccharides is followed by the sequential action of lysosomal exoenzymes to reduce the resulting oligosaccharides to monosaccharides and inorganic sulfate. Mucopolysaccharidosis (MPS) type II is a lysosomal storage disorder caused by a deficiency of the exoenzyme iduronate-2-sulfatase (I2S).