MPS III has four different subtypes designed as MPS III type A (MPS IIIA), MPS III type B (MPS IIIB), MPS III type C (MPS IIIC), and MPS III type D (MPS IIID), caused by the deficiency of one of the four lysosomal specific enzymes, heparan N-sulfatase (sulfamidase) (SGSH), alpha-N-acetylglucosaminidase (NAGLU), acetyl CoA-alpha-glucosaminidase N-acetyltransferase (HGSNAT) and N-acetylglucosamine-6-sulfatase (GNS), respectively. The gene discussed is GNS; the disease is mucopolysaccharidosis type 3B.