GNS and mucopolysaccharidosis type 3: Mutations in four different genes can lead to Sanfilippo syndrome (A: SGSH encodes heparan-N-sulfatase (EC 3.10.1.1), B: NAGLU encodes α-N-acetylglucosaminidase (EC 3.2.1.50), C: HGSNAT encodes acetyl-CoA:α-glucosaminide N-acetyltransferase (EC 2.3.1.78), and D: GNS encodes N-acetylglucosamine-6-sulfatase (EC 3.1.6.1)).