Sanfilippo syndrome, or Mucopolysaccharidosis III (MPS-III) is a rare and progressive autosomal recessive lysosomal storage disease. It is caused by a deficiency in one of the enzymes needed to break down the glycosaminoglycan heparan sulfate (which is found in the extra-cellular matrix and on cell surface glycoproteins). In people with this disorder, the body cannot break down a large sugar molecule called heparin sulfate. Signs and symptoms usually begin in early childhood and include severe neurological symptoms such as progressive dementia, aggressive behavior, hyperactivity, seizures, deafness, loss of vision, and an inability to sleep for more than a few hours at a time. MPS IIIA is caused by mutations in the SGSH gene and is inherited in an autosomal recessive manner. There is currently no specific treatment for MPS IIIA; affected individuals usually do not survive past the second decade of life.
Although a diagnosis of Sanfilippo syndrome is typically confirmed by a biochemical genetic test called an enzyme assay, carrier testing with an enzyme assay is generally unreliable due to a wide variation in enzyme concentrations. If molecular genetic testing (which looks at the DNA) has been done on the affected family member and the mutation(s) have been identified, molecular genetic testing can then also be used to identify carriers among siblings or other relatives.