Sanfilippo A syndrome (MPS IIIA) is an autosomal recessive rare disease, caused by mutations in the N-sulfoglucosamine sulfohydrolase (SGSH) gene that lead to a deficiency of the heparan-N-sulphatase (sulphamidase) enzyme and subsequent accumulation of heparan sulphate (HS) and partially degraded products in the lysosomes of different organs. The gene discussed is SGSH; the disease is mucopolysaccharidosis type 3A.