Mucopolysaccharidosis type IIIA (MPS-IIIA, Sanfilippo A) is one of the most severe lysosomal storage disorder (LSD) caused by the inherited deficiency of sulfamidase, a lysosomal sulfatase enzyme involved in the stepwise degradation of heparan sulfates (HS). The gene discussed is SGSH; the disease is lysosomal storage disease.