Hunter syndrome

Hunter syndrome, also known as mucopolysaccharidosis type II (MPS II), is a rare genetic condition that impacts many parts of the body. It is considered a progressively debilitating condition, though the rate and severity of progression can vary.

What causes Hunter syndrome?

The body relies on the enzyme iduronate-2-sulfatase (I2S) to help break down large sugar molecules called glycosaminoglycans, or GAGs. In people living with Hunter syndrome, a genetic mutation prevents their body from making I2S. As a result, GAGs accumulate inside the body’s cells, causing widespread symptoms that worsen over time.vi

What are the symptoms of Hunter syndrome?

Hunter syndrome affects the entire body, but its severity can range from attenuated (less severe) to neuronopathic (more severe) depending on the degree of brain involvement and cognitive impairment.vi

People with the attenuated form typically live into adulthood with minimal cognitive impairment, whereas people with the neuronopathic form experience severe neurodevelopmental decline and have a shortened life expectancy.vi

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How can symptoms of Hunter syndrome be managed?

Treatment options for Hunter syndrome aim to address the deficiency of the I2S enzyme.vii,viii In the U.S., there are two approved enzyme replacement therapies for the treatment of Hunter syndrome.
 
Our pipeline includes an investigational gene therapy designed to deliver a version of the gene responsible for I2S directly to CNS cells, potentially enabling long-term I2S production following a one-time administration.iv

Our science is impactful

We go beyond symptom management, providing patients with potentially disease-modifying
treatment options that could improve and extend quality time with loved ones.

Gene Therapy Science

Gene therapy science

Gene therapy has the potential to address critical genetic mutations, like those causing Hunter syndrome.

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treat Duchenne muscular dystrophy.

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JAK1 inhibition science

JAK1 inhibition science

JAK1 inhibition is being developed
to treat EGPA, a type of vasculitis.

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Gene Therapy Science

Gene therapy science

Gene therapy has the potential to address critical genetic mutations, like those causing Hunter syndrome.

Explore gene therapy

Exon-skipping science

Exon-skipping science

Exon-skipping has the potential to
treat Duchenne muscular dystrophy.

Explore exon-skipping

JAK1 inhibition science

JAK1 inhibition science

JAK1 inhibition is being developed
to treat EGPA, a type of vasculitis.

Explore JAK1

Sources

i MedlinePlus. Genetic Disorders. Available at:https://medlineplus.gov/geneticdisorders.html. Accessed December 2025.
ii MedlinePlus. What is Gene Therapy? https://medlineplus.gov/genetics/understanding/therapy/genetherapy/. Updated October 5, 2023. Accessed December 2025.
iiiMedlinePlus. How Does Gene Therapy Work? https://medlineplus.gov/genetics/understanding/therapy/procedures/. Updated October 5, 2025. Accessed December 2025.
iv Data on File.
v Wraith JE, Scarpa M, Beck M, et al. Mucopolysaccharidosis type II (Hunter syndrome): a clinical review and recommendations for treatment in the era of enzyme replacement therapy. Eur J Pediatr. 2008;167(3):267-277.doi:10.1007/s00431-007-0635-4.
vi MedlinePlus. Mucopolysaccharidosis type II.
https://medlineplus.gov/genetics/condition/mucopolysaccharidosis-type-ii/. Updated October 5, 2023. Accessed December 2025.
viiD’Avanzo F, Rigon L, Zanetti A, Tomanin R. Mucopolysaccharidosis Type II: One Hundred Years of Research, Diagnosis, and Treatment. Int J Mol Sci. 2020;21(4):1258. Published 2020 Feb 13. doi:10.3390/ijms21041258
viii Stapleton M, Kubaski F, Mason RW, et al. Presentation and Treatments for Mucopolysaccharidosis Type II (MPS II;Hunter Syndrome). Expert Opin Orphan Drugs. 2017;5(4):295-307. doi:10.1080/21678707.2017.1296761.
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