After the fragmentation, the following enzymes proceed with the complete degradation of the small fragments by acting sequentially (Figure 1): iduronate 2-sulfatase (IDS), α-L-iduronidase (IDUA), heparan N-sulfatase or sulfamidase (SGSH, mutated in Sanfilippo syndrome type A), acetyl-CoA α-glucosaminide N-acetyltransferase (HGSNAT, mutated in Sanfilippo syndrome type C), α-N-acetylglucosaminidase (NAGLU, mutated in Sanfilippo syndrome type B), glucuronate 2-sulfatase (GDS), β-glucuronidase (GUSB), and N-acetylglucosamine 6-sulfatase (GNS, mutated in Sanfilippo syndrome type D) [26]. The gene discussed is GNS; the disease is mucopolysaccharidosis type 3B.