WASHINGTON, D.C. — Children with a rare genetic disorder that affects the brain and body will have access to a newly approved treatment designed to slow disease progression, federal regulators announced.
What This Means for You
- Families affected by Hunter syndrome now have a treatment targeting brain-related symptoms
- The drug may slow disease progression if started early in young children
- Approval was accelerated, meaning further studies are still required
The U.S. Food and Drug Administration approved Avlayah, a weekly intravenous treatment, for certain pediatric patients with Hunter syndrome, a rare inherited condition that causes harmful sugar molecules to build up in the body and damage organs.
Hunter syndrome, also known as Mucopolysaccharidosis type II, disrupts physical and neurological development by causing the accumulation of substances that impair the skeleton, heart, lungs, and brain.
First Treatment Targeting Neurologic Symptoms
FDA officials said Avlayah is the first approved therapy specifically aimed at addressing neurological complications of the disease, which affects about 500 people in the United States, primarily males.
The treatment is intended for children weighing at least 5 kilograms and must be started before advanced neurological damage occurs to be most effective.
“Today is a milestone day for children and their families battling Hunter syndrome,” said FDA Commissioner Marty Makary.
How the Drug Works
Avlayah was approved under an accelerated pathway, which allows earlier access to promising treatments based on indicators that are reasonably likely to predict clinical benefit.
In this case, approval was based on the drug’s ability to reduce levels of heparan sulfate — a substance that accumulates in the brain and contributes to organ damage — in cerebrospinal fluid.
Regulators said reductions in this substance are linked to improved disease outcomes, though additional studies are ongoing to confirm long-term clinical benefits.
Clinical Trial Results
The approval was supported by a clinical trial involving 47 pediatric patients ranging from 3 months to 13 years old.
Among 44 patients evaluated after 24 weeks of treatment, researchers reported an average 91% reduction in heparan sulfate levels. Most patients achieved levels below the upper limit of normal.
Safety and Monitoring Requirements
The drug carries a boxed warning — the FDA’s most serious safety alert — for potential allergic reactions, including life-threatening anaphylaxis.
Patients must begin treatment in a monitored health care setting. Common side effects include infections, fever, anemia, cough, gastrointestinal symptoms, and skin reactions.
Doctors are advised to monitor blood counts and kidney function during treatment due to risks of anemia and kidney disease.
Next Steps
The drug’s manufacturer, Denali Therapeutics, is conducting a larger randomized clinical trial to confirm the treatment’s long-term benefits.
The FDA granted the drug multiple expedited designations, including breakthrough therapy and priority review, to accelerate its development and approval for this rare condition.
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