Overview
Hunter Syndrome
Learn about the disease that drives our cause and affects the lives of our community.
THE BIG PICTURE
What is Hunter Syndrome?
Think of it this way: when your garbage can gets full, you take out the trash. But what if you can’t? What if bag after bag fills up, taking over your kitchen? Soon, it would be hard to walk around, cook, or clean. As the trash builds even higher, your kitchen becomes unusable. Similarly, children with Mucopolysaccharidosis Type II (MPS II), also known as Hunter syndrome, are unable to make the enzyme that takes care of our cellular garbage; their bodies becoming like the kitchen in this example.
Hunter syndrome is a rare genetic disease that is progressively debilitating, life-limiting and without a cure. It occurs almost exclusively in males and currently affects approximately 500 boys in the U.S. and less than 2,000 worldwide. Individuals with Hunter syndrome have a defect in the gene that normally causes the body to make the enzyme iduronate-2-sulfatase (I2S) – the “garbage man” – which is responsible for the breakdown of cellular waste called glycosaminoglycans or GAGs – the cell’s “garbage.” Without that necessary enzyme, the accumulation of these GAGs leads to progressive damage throughout the entire body.
Currently Approved Treatments
ELAPRASE (idursulfase)
Elaprase is an FDA-approved enzyme replacement therapy (ERT) that replaces the missing iduronate-2-sultatase enzyme, and is given rough weekly through intravenous infusions and can help reduce many of the somatic (body-related) symptoms of Hunter syndrome. However, it does not cross the blood-brain barrier and does not treat cognitive symptoms.
This treatment involves transplanting healthy donor stem cells into a child with Hunter syndrome. It may slow disease progression in some individuals, particularly when performed early. However, HSCT carries significant risks and is not widely used for Hunter syndrome. It is typically considered only in select cases and should be discussed thoroughly with a qualified medical team.
To learn more, speak to your provider.
AVLAYAH is a FDA-approved enzyme replacement therapy (ERT) that crosses the blood-brain barrier to reach the brain in addition to the body. AVLAYAH is approved for the treatment of neurologic symptoms in pediatric patients weighing at least 5 kg with Hunter syndrome prior to advanced neurologic disease. This approval is based on a reduction of heparan sulfate (HS) in the cerebrospinal fluid (CSF) surrounding the brain and spinal cord. Studies are ongoing to confirm how well it works in improving clinical symptoms. AVLAYAH is not recommended for use in combination with other enzyme replacement therapies for the treatment of Hunter syndrome.
Emerging Therapies in Development
RGX-121
A gene therapy designed to deliver the I2S gene directly to the central nervous system using a one-time infusion.
JR-141
A fusion protein that combines the I2S ezyme with an antibody to cross the blood-brain barrier. It is a weekly infusion.
Autologous Gene-Edited Hematopoietic Stem Cell Transplant
A stem cell-based gene therapy approach using a patient’s own modified cells.
Prenatal Enzyme Replacement Therapy
A groundbreaking investigational approach where enzyme replacement is delivered before birth to potentially prevent early damage.
Common Terminology in Hunter Syndrome
WHAT TO LOOK FOR
Signs and Symptoms
Learn about how Hunter syndrome presents itself and the signs and symptoms that are commonly seen through those affected.
November 14, 2026
Cure Within Reach Gala
Join us for an unforgettable evening at the Cure Within Reach Gala, a premier event dedicated to bringing hope to the Hunter syndrome community. Hosted at the beautiful Georgia Aquarium in Atlanta, GA.