What Is Sanfilippo Syndrome?

Medically Reviewed by Dany Paul Baby, MD on April 20, 2022
5 min read

Sanfilippo syndrome — also known as mucopolysaccharidosis type III — is a rare life-threatening disorder that interferes with metabolism. While it doesn’t have a cure, some symptoms can be treated to alleviate this condition. Here’s everything you need to know.

Sanfilippo syndrome is a genetic disorder that affects your child’s metabolism. A person with this condition lacks a key enzyme that breaks down a type of waste produced by the body.

Enzymes are proteins that help you break down — or metabolize — various substances including food materials like sugar. Within your cells, they are located in sacs called lysosomes. These lysosomes are affected in Sanfilippo syndrome — that's why this disorder is regarded as a lysosomal storage disease.

Specifically, Sanfilippo makes the body unable to metabolize a molecule called heparan sulfate — a natural cellular waste, which is usually disposed of and recycled through enzyme action. As a result, heparan sulfate starts to build up in the cells and stops them from functioning correctly. This eventually leads to organ damage, mental and growth disorders, and behavioral problems.

Sanfilippo syndrome is seen in 1 in 70,000 births in the U.S., and children with it have a life expectancy of 10 to 20 years. While it’s considered a rare disease, having a family history of it increases the risk for your child.

Normally, four enzymes are responsible for the breakdown of heparan sulfate — so Sanfilippo syndrome also has four types classified on the basis of the missing enzyme type. While some types are less aggressive than others, the life expectancy will vary only slightly.

Sanfilippo syndrome Type A. This type is the most common and also the most severe. Children with this type will usually lose their motor skills early, and they'll display other advanced Sanfilippo syndrome symptoms at a premature age.

Sanfilippo syndrome Type B. This type is less common and usually progresses more slowly than type A.

Sanfilippo syndrome Types C and D. These are two of the least common kinds of Sanfilippo syndrome — with Type D being the rarest of all four types. Though their progression rates can vary, they’re generally slower to progress than Types A and B. 

Sanfilippo syndrome often goes unnoticed during the first months — or even years — of a child's life. Even though there may be some signs at an early age, doctors usually confuse them for other conditions.

Most of the Sanfilippo syndrome symptoms start at the age between 1 and 6 years — they include developmental delay, trouble sleeping, and frequent infections.

Common symptoms seen at the first Sanfilippo syndrome stage include:

  • Behavioral issues
  • Speech and development delays
  • Persistent diarrhea
  • Frequent infections, especially in the ear and throat
  • Trouble sleeping

As the disorder progresses, a child with Sanfilippo syndrome will start displaying even more severe symptoms. Often, kids at this stage need to use a feeding tube because they lose their motor skills by then. During this stage, sleep and behavioral issues become more pronounced.

The second stage of Sanfilippo syndrome is marked by these symptoms:

  • Extreme restlessness
  • Gradual loss of language
  • Hyperactivity
  • Hearing loss
  • Seizures
  • Progressive intellectual disability

In the final stage, an affected child will lose their motor skills, which will slow them down considerably. Movement disorders and loss of walking ability are common, and at this stage, most children aren’t able to speak or eat anything. Children at this stage will usually show:

  • Movement disorders
  • Contractures of hands and fingers
  • Frequent falling
  • Arthritis
  • Visual impairment

Because it’s a rare disease, most doctors won’t be able to usually diagnose Sanfilippo syndrome during its early stages. Instead, they might consider other conditions like autism and ADHD because their symptoms also include developmental issues and hyperactivity.

Generally, Sanfilippo syndrome is easier to diagnose in the second stage when the affected child may be 1 to 6 years old. To confirm the diagnosis, the doctor will order a urine test. The result of this will tell the doctor if the child’s urine heptane sulfate levels are too high. If yes, they might order a blood test to check if the related enzyme is missing too. If the enzyme is missing, they might ask for genetic testing to further verify their diagnosis.

There's no cure for Sanfilippo syndrome. But several symptom-specific treatments can be prescribed to elevate the affected child’s quality of life. 

There are a few possible therapeutic avenues under research that may help treat Sanfilippo syndrome in the future. One such avenue is enzyme-replacement therapy, where the child is injected with an infusion of the enzyme they can’t produce — which allows them to metabolize heparan sulfate until the next injection.

Another possible treatment is gene therapy, which provides the child with a working gene to replace the previous one. After that, their body has the ability to metabolize heptane sulfate on its own.

These procedures are still under investigation so they may not be available in the near future. In the meantime, check with a specialist if you suspect that your child has Sanfilippo syndrome symptoms.

Sanfilippo syndrome can’t be prevented, but you can try to minimize risks by checking your family history. Your child is at risk of getting Sanfilippo syndrome if both you and your partner carry the affected gene. Another good way of minimizing Sanfilippo syndrome risk as much as possible is to check if your newborn screening has a relevant test for it. While most don’t, there are a few private ones you can order online that include it.

If your child is diagnosed as having Sanfilippo syndrome, get in contact with a specialist as soon as you can. Specific symptoms of this disease can be treated to improve your child’s quality of life.

Yet, because it’s such a rare condition, you might find it difficult to find experts on this topic. In that case, specialized organizations like Cure Sanfilippo Foundation and Team Sanfilippo may be of great help.