MPS III (Sanfilippo Syndrome)
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Overview
MPS III is a mucopolysaccharide disease also known as Sanfilippo Syndrome. It takes its name from Dr. Sylvester Sanfilippo, one of the U.S. doctors who described the condition in 1963.
There is no cure for MPS III and no current approved treatment. Enzyme replacement therapy (ERT) has not been shown to be effective in MPS III. Bone marrow transplants have been tried on individuals with MPS III, but with disappointing results. Gene therapy, chaperone therapy and intrathecal enzyme therapy are a few of the treatments for MPS III where research is ongoing.
Approximately 1 in 70,000 newborns are born with MPS III. MPS III A and MPS III B are more common than MPS III C and MPS III D.
Understanding the Cause of MPS and ML
Mucopolysaccharides are chains of sugar molecules used to build connective tissues in the body.
“muco” refers to the thick jelly-like consistency of the molecules
“poly” means many
“saccharide” is a general term for a sugar molecule
The body constantly replaces used materials and breaks them down for disposal. MPS III patients are missing an enzyme essential to breaking down the mucopolysaccharide heparan sulphate. These materials remain stored in the body’s cells, causing progressive damage. Babies may show little sign of the disease, but as cells sustain damage, symptoms start to appear.
Understanding the Inheritance of the Disease
MPS III is caused by a recessive gene. There is a one in four chance with every pregnancy that the child will inherit the variant gene from each carrier parent and will be affected with the disease. There is a two in three chance that unaffected brothers and sisters of MPS III patients will be carriers.
Common Questions
What are the differences in each subtype of MPS III?
MPS III, or Sanfilippo syndrome, includes four subtypes (A, B, C, and D), each caused by a deficiency in a different enzyme needed to break down certain sugars in the body. While all subtypes lead to similar symptoms—primarily progressive neurological decline including developmental delay, behavioral challenges, and loss of skills—the severity and progression can vary slightly depending on the subtype.
- Types A and B are the most common and tend to progress faster and more severely.
- Types C and D are rarer and may have a somewhat slower progression, but still lead to significant neurological challenges.
All subtypes mainly affect the brain and nervous system, and currently, there are no approved treatment options. Care focuses on individualized support and improving quality of life.
Are there attenuated forms of Sanfilippo syndrome?
While Sanfilippo syndrome is typically a progressive condition that primarily affects the brain and nervous system, some individuals experience a milder, slower-progressing form—often called an attenuated form. In these cases, symptoms may develop later and progress more slowly, allowing for a longer period of better functioning.
Because MPS III can vary widely from person to person, it’s important for families to work closely with their healthcare team to understand their loved one’s unique journey and needs.
How do the different clinical trial processes work, and where do we go to learn more?
Clinical trials are research studies that test new treatments to see if they are safe and effective for people with MPS III. These studies often happen in phases—starting small to evaluate safety, then expanding to understand how well a treatment works, and finally comparing it to current care standards.
Because MPS III affects the brain and nervous system, many trials focus on treatments that can reach the brain and slow or stop disease progression. Participation is voluntary and carefully monitored by medical experts.
To learn more about current and upcoming clinical trials, families can visit trusted sources like:
- ClinicalTrials.gov — a comprehensive database of clinical studies worldwide.
- The National MPS Society website and support team, who can provide guidance, answer questions, and connect you with trial information.
- Your child’s medical team, who may know about local or specialized trial opportunities.
Clinical Trials
Clinical trials are research studies that determine whether treatments or devices are safe for humans. These studies also look for effective medical approaches for specific conditions and help provide reliable data for patients, researchers and doctors.
Clinical trials are conducted on small groups to determine whether a drug or procedure causes negative reactions or unsatisfactory side effects.
Treatments
There are currently no approved treatments for MPS III. Enzyme replacement therapy (ERT) has not been shown to be effective in MPS III. Bone marrow transplants have been tried on individuals with MPS III but results were not positive. Current MPS III research is focusing on gene therapy, chaperone therapy and intrathecal enzyme therapy.
Emerging Treatments
There are a number of emerging treatments and therapies currently in development at the following companies:
Palliative Care
Palliative care is any form of medical care or treatment that concentrates on reducing the severity of disease symptoms. The goal is to prevent and relieve suffering and to improve quality of life for people facing serious, complex illness. This includes respite care, symptom management and bereavement support and may extend over a period of time. Many hospitals have palliative care centers.
Need Support? We’re Here for You
Living with an MPS diagnosis can feel overwhelming, but you’re not alone. Our Family Support Programs offer guidance, resources, and a caring community to help you every step of the way.
