Little clinical difference exists between these four types but symptoms appear most severe and seem to progress more quickly in children with type A. The average duration of Sanfilippo syndrome is 8 to 10 years following onset of symptoms. Most persons with MPS III live into their teenage years, and some live longer. Sanfilippo A is the most severe of the MPS III disorders and is caused by the missing or altered enzyme heparan N-sulfatase. Children with Sanfilippo A have the shortest survival rate among those with the MPS III disorders. Sanfilippo B is caused by the missing or deficient enzyme alpha-N-acetylglucosaminidase. Sanfilippo C results from the missing or altered enzyme acetyl-CoAlpha-glucosaminide acetyltransferase. Sanfilippo D is caused by the missing or deficient enzyme N-acetylglucosamine 6-sulfatase.The incidence of Sanfilippo syndrome (for all four types combined) is about one in 70,000 births. MPS IV
MPS IV, Morquio syndrome, is estimated to occur in 1 in 700,000 births. Its two subtypes result from the missing or deficient enzymes N-acetylgalactosamine-6-sulfatase (GALNS) (Type A) or beta-galactosidase (Type B) needed to break down the keratan sulfate sugar chain. Clinical features are similar in both types but appear milder in Morquio Type B. Onset is between ages 1 and 3. Neurological complications include spinal nerve and nerve root compression resulting from extreme, progressive skeletal changes, particularly in the ribs and chest; conductive and/or neurosensitive loss of hearing and clouded corneas. Intelligence is normal unless hydrocephalus develops and is not treated.
The incidence of Hunter syndrome is estimated to be 1 in 100,000 to 150,000 male births. MPS III
MPS III, Sanfilippo syndrome, is marked by severe neurological symptoms. These include progressive dementia, aggressive behavior, hyperactivity, seizures, some deafness and loss of vision, and an inability to sleep for more than a few hours at a time. This disorder tends to have three main stages. During the first stage, early mental and motor skill development may be somewhat delayed. Affected children show a marked decline in learning between ages 2 and 6, followed by eventual loss of language skills and loss of some or all hearing. Some children may never learn to speak. In the syndromes second stage, aggressive behavior, hyperactivity, profound dementia, and irregular sleep may make children difficult to manage, particularly those who retain normal physical strength. In the syndromes last stage, children become increasingly unsteady on their feet and most are unable to walk by age 10. Thickened skin and mild changes in facial features, bone, and skeletal structures become noticeable with age. Growth in height usually stops by age 10. Other problems may include narrowing of the airway passage in the throat and enlargement of the tonsils and adenoids, making it difficult to eat or swallow. Recurring respiratory infections are common. There are four distinct types of Sanfilippo syndrome, each caused by alteration of a different enzyme needed to completely break down the heparan sulfate sugar chain.