Mutations in the HGSNAT gene cause mucopolysaccharidoses III type or Sanfilippo syndrome type C due to a deficiency of acetyl-CoA a-glucosaminide N-acetyltransferase (EC 2.3.1.78) that catalyzes the degradation of heparan N-sulfatase (sulfamidase). The gene discussed is SGSH; the disease is mucopolysaccharidosis type 3C.