Mucopolysaccharidosis type IIIA (MPS IIIA) - Ultragenyx Patient Advocacy

Also known as Sanfilippo syndrome type A, MPS IIIA

What is it?

Mucopolysaccharidosis type IIIA (MPS IIIA), also called Sanfilippo syndrome type A, is a severe, progressive disorder that primarily affects the brain and spinal cord (central nervous system). Other body systems can also be involved, although the physical features are usually mild in the early stages. In people with MPS IIIA, the body cannot break down a large sugar molecule called heparan sulfate (HS).

What Causes It?

Mucopolysaccharidoses are a group of lysosomal storage diseases caused by the absence or malfunctioning of certain enzymes the body needs to break down molecules called glycosaminoglycans. Glycosaminoglycans are chains of sugar molecules (carbohydrates) in each of our cells. MPS IIIA is caused by gene alterations to the SGSH impacting the enzyme called N-sulfoglucosamine sulfohydrolase which is responsible for breaking down the GAG heparan sulfate. In MPS IIIA, heparan sulfate accumulates and causes cell death and progressive damage.

Are There Different Types of MPS III?

There are four distinct types of MPS III, each caused by alteration of a different enzyme needed to completely break down the heparan sulfate sugar chain.

MPS IIIA is caused by the missing or altered enzyme heparan N-sulfatase
MPS IIIB is caused by the missing or deficient enzyme alpha-N-acetylglucosamine
MPS IIIC results from the missing or altered enzyme acetyl-CoA: alpha-glucosaminide
MPS IIID is caused by the missing or deficient enzyme N-acetylglucosamine-6-sulfate

While each subtype of MPS III is associated with different enzyme deficiency, all MPS III patients lack the ability to break down the GAG heparan sulfate (HS).

What Are Some Common Symptoms?

Signs of MPS IIIA can be present in the newborn period of a child’s life, but often go unnoticed. Most 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. The physical features of MPS IIIA are less pronounced than those of other types of mucopolysaccharidosis. Individuals with MPS IIIA typically have mildly “coarse” facial features, a large head (macrocephaly), a slightly enlarged liver (mild hepatomegaly), and a soft out-pouching around the belly-button (umbilical hernia) or lower abdomen (inguinal hernia). Some may have short stature, joint stiffness, or mild dysostosis multiplex, which refers to multiple skeletal abnormalities seen on x-ray. Affected individuals often experience chronic diarrhea and recurrent upper respiratory and ear infections.

How Many People Have MPS III?

It is estimated that fewer than 1 in 70,0000 newborns are born with MPS III.

MPS IIIA: with an estimated frequency of 1 in 60,000 newborns
MPS IIIB: with an estimated frequency of 1 in 95,000 newborns
MPS IIIC: with an estimated frequency of 1 in 230,000 newborns
MPS IIID: with an estimated frequency of 1 in 1,000,000 newborns

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MPS III Patient Advocacy Groups*

US Organizations

*These organizations are an incomplete listing of rare disease advocacy groups and are not controlled by, endorsed by, or affiliated with Ultragenyx Pharmaceutical Inc. The list is meant for informational purposes only and is not intended to replace your healthcare professional’s medical advice. Ask your doctor or nurse any questions you may have about your disease or treatment plan. If you would like to have your group added to the list, please contact [email protected].

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