Hunter Syndrome (MPS II) Clinical Trials and Treatments

Hunter syndrome (mucopolysaccharidosis type II) is an X-linked lysosomal storage disorder caused by deficiency of iduronate-2-sulfatase, an enzyme essential for degrading heparan sulfate and dermatan sulfate glycosaminoglycans. Without adequate enzyme activity, these substrates accumulate within lysosomes in cells throughout the body. The severe form typically manifests between ages 2-4 years with developmental delay, coarse facial features, hepatosplenomegaly, joint stiffness, and progressive neurological decline including intellectual disability and behavioral problems.

The most common symptoms of Hunter Syndrome include Developmental delay and behavioral problems, Coarse facial features and thickened skin, Growth retardation and short stature, Hearing loss, often conductive and sensorineural, Joint stiffness and reduced mobility, among others. Hunter Syndrome affects approximately 1 in 100,000 to 150,000 males; females with disease are rare. Symptoms can range from mild to severe and may vary between individuals.

Trial Friend lists all active clinical trials for Hunter Syndrome from ClinicalTrials.gov, with eligibility criteria translated into plain English. Patients can filter by trial phase and recruitment status, search by location, and use the Match Me tool to score trials against their profile. Hunter syndrome treatment has evolved with enzyme replacement, and research continues advancing therapeutic approaches. On March 24, 2026 the FDA granted accelerated approval to tividenofusp alfa (Avlayah), a weekly IV enzyme therapy built to cross the blood-brain barrier, to treat the brain-related (neurologic) effects of Hunter syndrome in children who weigh at least 5kg and do not yet have advanced neurologic impairment.

Yes. As of October 21, 2026, 2 FDA-approved medicines have a current label that names Hunter Syndrome: Avlayah (tividenofusp alfa), first approved in 2026; and Elaprase (idursulfase), first approved in 2006. Corticosteroids and immune globulins count once each.

Hunter Syndrome is caused by variants in the IDS gene. Almost exclusively affects males; female carriers are rarely symptomatic.

It is X-linked, so it mainly affects boys, and a mother who carries the variant has a 1 in 2 chance of passing it to each son. The condition affects approximately 1 in 100,000 to 150,000 males; females with disease are rare. Genetic testing confirms the diagnosis.

Yes. Genetic testing for Hunter Syndrome looks at the IDS gene. Almost exclusively affects males; female carriers are rarely symptomatic.

It is X-linked, so it mainly affects boys, and a mother who carries the variant has a 1 in 2 chance of passing it to each son.

A confirmed variant establishes the diagnosis and is often required to enroll in gene-specific trials. The labs currently offering the test are listed in the Genetic Testing section of this page, pulled live from the NIH Genetic Testing Registry. A genetic counselor can help interpret the result and decide which relatives should be tested.

Eligibility for Hunter Syndrome clinical trials depends on factors like age, diagnosis, treatment history, and overall health. Each trial sets its own inclusion and exclusion criteria. Trial Friend translates these requirements from medical language into plain English so patients can review them more easily. The Match Me tool can score your profile against active trials to help identify studies that may be a fit.

Participating in a Hunter Syndrome clinical trial typically involves scheduled visits, medical tests, and close monitoring by a research team. Depending on the study phase, you may receive an investigational treatment, a placebo, or the current standard of care. Trials may last from a few weeks to several years. Study participation is voluntary, and you can withdraw at any time.