Page reviewed by:
Dr. Cara O’Neill, FAAP

Page last updated:
June 15, 2023

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What Is Sanfilippo Syndrome?

Imagine Alzheimer’s and dementia, but in children.

In a nutshell, that’s what every family of children with Sanfilippo Syndrome faces.

Sanfilippo Syndrome — also known as Mucopolysaccharidosis type III or MPS III — is a terminal, neurodegenerative rare disease. It causes children to lose all the skills they’ve gained, suffer seizures and movement disorders, experience pain and suffering, and then die, often before the second decade of life.

Because of its neurodegenerative nature and multi-system impact, Sanfilippo Syndrome is often called “childhood Alzheimer’s” or “childhood dementia.”

Currently there is no FDA-approved treatment or cure. But there is research happening and there is hope.

There are subtypes of Sanfilippo Syndrome

Four subtypes of Sanfilippo, or Mucopolysaccharidosis type III, have been identified – Types A, B, C, and D. The subtypes can also be referred to as MPS IIIA, MPS IIIB, MPS IIIC, and MPS IIID or Sanfilippo A, Sanfilippo B, Sanfilippo C, and Sanfilippo D.

Each subtype corresponds to a particular enzyme that is missing or not working properly in the body’s process of breaking down heparan sulfate.

In most of the world, Type A is the most common subtype, making up more than half of the cases. Types B and C are less common, and Type D is the rarest.

Type A is typically considered the most-severe subtype of Sanfilippo. This means that most people with Type A have a rapidly-progressing form with earlier loss of abilities, such as talking and walking, and an earlier age of death. Type B may progress somewhat less rapidly, on average. Types C and D have more variable progression rates, but most persons tend to retain skills longer than in A and B.

Learn more about the symptoms, how to get diagnosed, prognosis, current research, and more below.

Figure depicting progressive disability of Sanfilippo Syndrome in child compared to a neurotypical child

One family’s story

This video is the story of Eliza O’Neill and her family. It’s a story similiar to the one every Sanfilippo family experiences. Please take a moment to watch.

How Common Is Sanfilippo Syndrome?

It is estimated that Sanfilippo Syndrome affects 1 in every 70,000 births. However, the prevalence could be higher. The true number will only be known when Sanfilippo is included in newborn screening.

Sanfilippo is classified as a rare disease because it affects fewer than 200,000 in the U.S., a definition that was established in the Orphan Drug Act of 1983.

Sanfilippo is one of more than 50 lysosomal storage disorders, which is a category of metabolic diseases.

Sanfilippo is named for Dr. Sylvester Sanfilippo, the Minnesota pediatrician and researcher who first described the enzyme defect that causes the disorder. He first presented his findings in 1963 at the annual meeting of the American Pediatrics Society.

What Causes Sanfilippo Syndrome?

Children with Sanfilippo Syndrome are born with a single genetic defect, a single change in their DNA, that causes their bodies to lack a necessary enzyme.

Because of the lack of enzyme, their bodies are unable to breakdown heparan sulfate, a natural cellular waste. Instead, their bodies and particularly brains become clogged with toxic levels, which causes a cascade of detrimental effects and ultimately death.

What Are the Symptoms and Prognosis?

Signs of Sanfilippo can be present in the newborn period of a child’s life, but often go unnoticed without newborn screening. Most symptoms typically begin to be recognized between 1 and 6 years of age when the child begins showing signs of developmental delay.

Relentless and devastating, Sanfilippo has a 100% mortality rate, with children typically passing away in their early teens.

How Is Sanfilippo Syndrome Diagnosed?

It often takes years to receive a correct diagnosis of Sanfilippo Syndrome. Due to its rarity and lack of physician awareness, a child’s symptoms are often classified as developmental delay and/or Autism until a thorough medical workup is done to identify the underlying cause.

Learn about the options for getting your child screened for Sanfilippo.

Where Does Research For a Cure Stand?

Today, there is no FDA-approved treatment or cure for Sanfilippo Syndrome.

Clinical trials for treatments, such as enzyme replacement therapy and gene therapy, are happening and other treatment strategies are in pre-clinical research and require funding.

Has Your Child Been Diagnosed with Sanfilippo?

If your child has been diagnosed with Sanfilippo or is currently awaiting testing, we are here for you.

Download our guide for newly-diagnosed families that walks you through the initial questions most families have about Sanfilippo, including what to do next. Plus, you will find additional information about Sanfilippo, how to contact us to discuss your family’s unique situation, and an exploration of current research and clinical trials.

Help Simon - Simon's parents looking at him