Fig. 1: Phenotypic and dysmorphic features of patient 1 (A and B),...
Hunter Syndrome (MPS II)
Hunter syndrome, also called mucopolysaccharidosis II or MPS II, is a rare disease that's passed on in families. It mainly affects boys. Their bodies can't break down a kind of sugar that builds bones, skin, tendons, and other tissue. Those sugars build up in their cells and damage many parts of the body, including the brain. Exactly what happens is different for every person.
When your son has Hunter syndrome, there are things you can do to help them play, have friends, and do some of the things that other kids do, even though they may look different from their pals.
Although there is no cure for Hunter syndrome, there are ways to help manage it and live with the symptoms.
Boys with the disease can't make a certain protein because there's a problem with a small piece of their DNA, called a gene, that comes from their mother.
A dad with Hunter syndrome will pass the problem gene to their daughter, but the daughter won't get the disease unless they get the gene from their mom, too.
It's possible -- but very, very unlikely -- that someone could develop Hunter syndrome even though no one in their family going back has had it.
When Hunter syndrome affects the brain, which is about 75% of the time, symptoms usually show up between 18 months and 4 years of age. They start about 2 years later when the disease is milder.
Hunter syndrome usually affects how the boy looks:
They'll probably have these symptoms:
When a boy's brain is affected, it's likely they'll have:
Kids who have Hunter syndrome are usually cheerful and affectionate, despite the problems it can cause.
Doctors often have to rule out other medical conditions first. Your doctor may ask:
If the doctors can't find another explanation for your son's symptoms, they'll test for Hunter syndrome by checking for:
After doctors are sure it's Hunter syndrome, it's a good idea to let extended family members know about the gene problem, too.
If you're a pregnant woman and you know you carry the gene or you already have a child with Hunter syndrome, you can find out whether the baby you're carrying is affected. Talk to your doctor about testing early in your pregnancy.
Early treatment may prevent some long-term damage.
Enzyme replacement therapy (ERT) can help slow the disease for boys with milder Hunter syndrome. It replaces the protein their body doesn't make. ERT can help improve:
ERT is the first treatment for kids whose brains aren't affected. It doesn't slow the disease in the brain.
Bone marrow and umbilical cord blood transplants. These transplants bring cells into your child's body that can hopefully make the protein they're missing. The new cells come from either a bone marrow donor whose cells match your child's or the stem cells of umbilical cord blood from newborn babies.
Both of these treatments are high-risk. They're usually used only if other treatments aren't possible. They also haven't been shown to help when the brain is affected.
Research is under way to find effective treatments for boys with severe Hunter syndrome.
Treating the symptoms. Because so many different parts of your child's body can be affected, you'll probably need to see several doctors to help you manage the condition, including:
Medication or surgery can ease some of the complications. Physical therapy can help with joint and movement issues. And occupational therapy can help you make changes at home and school to make it easier to get around and do things. Medications like melatonin may help with sleep.
Focus on keeping your son healthy and giving them the chance to live a meaningful, rewarding life. Include them in family activities whenever it's safe.
Set the tone for others. Be positive. Keep an open mind about other people; they may not know what to say so they don't pry or offend or embarrass you. When someone asks about them, be matter-of-fact about their condition. Talk about them as a person -- their interests, their curiosity, and their sunny personality, too. Let them know what their needs as well as their abilities are, and how they can help, if that's appropriate.
Activity. Start stretching and range-of-motion exercises early to keep their joints flexible. Ask your physical therapist about ways to make exercises part of play. Choose large toys that are easy to grab and hold on to, that won't be damaged by chewing.
Encourage friendships. Talk to other kids (or their parents) about how to interact with your son. Walk up to them from the front, with hands out. Give them about an arm's length of space. It's OK to remind them to touch nice and not hit. But kids will be kids, so prepare them for stares and teasing with role-play and humor.
Extra help for learning. Help them learn as much as they can while their brain is working well. If they go to school, work with the staff to come up with an individualized education program (IEP) for them. They may be eligible for one-on-one attention in the classroom or help for other issues, like hearing problems.
Take care of yourself, too. You'll do a better job caring for your child when you have people you can turn to to help out with caregiving tasks. Step back, and take a break to rest and recharge. Spend time nurturing your relationship with yourself and others you love. Remember, the whole family is affected by this disease. A counselor can help sort out feelings.
Some boys with less severe Hunter syndrome grow up and live long lives. They'll go through puberty like other teens and can have children. But heart disease and trouble breathing can still cause problems for them.
Kids with severe Hunter syndrome are less likely to reach adulthood. Their brains will slowly stop working, and eventually they'll need special care to make them comfortable.
Parents of other Hunter syndrome boys are a great resource for understanding what's going on, sharing your feelings, and getting ideas for how to live with the condition. You can find ways to enjoy the time that you have with your child.
The National MPS Society has more information about this disease. They can also help you connect with other families who are facing the same challenges.
If you are interested in more advanced reading on this topic, we've made content from our health professional site, Medscape, available to you on WebMD.
Learn More
Gene Therapy For Hunter Syndrome Under FDA Review
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GC Biopharma's Phase 3 Clinical Trial Results For Hunterase Published In SCIE-Indexed Journal
YONGIN, South Korea, May 30, 2025 /PRNewswire/ -- GC Biopharma, a South Korean pharmaceutical company, announced that the Phase 3 clinical trial results for Hunterase (idursulfase beta), its investigational drug for Hunter Syndrome (MPS II), have been published in Genetics in Medicine, an SCIE-indexed journal. Conducted at Samsung Medical Center, the Phase 3 clinical trial enrolled 24 newly diagnosed Hunter Syndrome patients with no prior treatment. It evaluated the efficacy and safety of Hunterase over a one-year treatment period.Hunter Syndrome is a rare genetic disorder caused by a deficiency of iduronate-2-sulfatase (IDS), an enzyme critical for glycosaminoglycan (GAG) catabolism. This deficiency leads to the progressive accumulation of GAGs in various organs and tissues, resulting in multisystemic dysfunction, including joint stiffness and hepatosplenomegaly.
The clinical trial results demonstrated that Hunterase significantly enhanced functional mobility, reduced urinary GAG concentrations, and markedly alleviated hepatosplenomegaly.
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By signing up with an email address, I acknowledge that I have read and agree to the Terms of Service and Privacy Policy.In the 6-Minute Walk Test (6-MWT), the primary endpoint of the study, patients treated with Hunterase walked an average of 62.2 meters more after treatment. This improvement was more than eight times greater compared to the placebo group, which saw an average increase of just 7.3 meters.
The 6-MWT measures the distance a patient can walk on a flat surface within 6 minutes. It is a widely used clinical measure for evaluating functional mobility, cardiopulmonary function, muscle strength, and overall physical health. In the context of Hunter syndrome, it serves as a standardized and meaningful indicator of disease progression and quality of life.
In addition to the primary endpoint, the study also achieved positive outcomes in secondary endpoints, including changes in urinary total glycosaminoglycan (GAG) levels, as well as heparan sulfate (HS) and dermatan sulfate (DS) levels. The GAG levels decreased by 71%, while HS and DS levels decreased by 89% and 88%, respectively. Moreover, liver and spleen volumes were reduced by 27% and 26%, respectively, demonstrating the drug's effectiveness in addressing organ enlargement commonly associated with the disease.
Hunterase also demonstrated a favorable safety profile. Most adverse events were mild or moderate, and no patients discontinued treatment due to side effects. Notably, only 19% of the patients had neutralizing antibodies detected three or more consecutive times, which is significantly lower than the 62.5% observed with the existing treatments. This suggests that Hunterase may offer a more sustained therapeutic effect compared to other currently available therapy.
"This clinical trial is especially meaningful as it represents the first Phase 3 study in Asian patients to validate the clinical efficacy of Hunterase", said Professor Young Bae Sohn of Ajou University School of Medicine and Ajou University Hospital, the journal's first author. "The results showed significant clinical improvement not only in metabolic markers but also in organ size normalization and restoration of physical mobility."
"We are thrilled to publish our encouraging phase 3 clinical trial results", stated Jae Uk Jeong, Head of R&D at GC Biopharma. "Hunterase, developed in Korea using our proprietary technology, has the potential to significantly improve the lives of patients with Hunter syndrome."
Hunter Syndrome is an X-linked lysosomal storage disorder, affecting approximately 1 in 100,000 male births. In severe cases, the patients experience early death before they reach adulthood, highlighting the need for early diagnosis and treatment. Currently, two treatments are widely available worldwide for Hunter Syndrome: GC Biopharma's Hunterase and Takeda's Elaprase.
About GC Biopharma
GC Biopharma (formerly known as Green Cross Corporation) is a biopharmaceutical company headquartered in Yong-in, South Korea. The company has over half a century of experience in the development and manufacturing of plasma derivatives and vaccines, and is expanding its global presence with successful US market entry of Alyglo™(intravenous immunoglobulin G) in 2024. In line with its mission to meet the demands of future healthcare, GC Biopharma continues to drive innovation by leveraging its core R&D capabilities in engineering of proteins, mRNAs, and lipid nanoparticle (LNP) drug delivery platform to develop therapeutics for the field of rare disease as well as I&I (Immunology & Inflammation). To learn more about the company, visit https://www.Gcbiopharma.Com/eng/
This press release may contain biopharmaceuticals in forward-looking statements, which express the current beliefs and expectations of GC Biopharma's management. Such statements do not represent any guarantee by GC Biopharma or its management of future performance and involve known and unknown risks, uncertainties, and other factors. GC Biopharma undertakes no obligation to update or revise any forward-looking statement contained in this press release or any other forward-looking statements it may make, except as required by law or stock exchange rule.
GC Biopharma Contacts (Media)
Sohee Kim
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Yelin Jun
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Yoonjae Na
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