Understanding Hunter Syndrome (MPS II): Causes, Symptoms, and Care
Updated: 3 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026
Quick Answer: What Is Hunter Syndrome?
Hunter syndrome (MPS II) is a genetic condition in which a missing enzyme, iduronate 2-sulfatase, prevents the body from breaking down certain sugar molecules, which build up in cells and damage tissues and organs. [1] Symptoms typically appear between ages 2 and 4 and include stiff joints, thickened facial features and developmental delays. [1] It almost exclusively affects boys. [1]
What the research says
Weekly enzyme replacement improves walking and lung function. In a randomized, placebo-controlled trial of 96 patients aged 5 to 31, weekly idursulfase added 37 m on the 6-minute walk test and 160 mL of forced vital capacity compared with placebo at 53 weeks (Muenzer et al., Genet Med, 2006). [2]
Treatment lowers the sugar buildup and shrinks enlarged organs. In a 12-patient randomized trial, urinary glycosaminoglycans fell 49% after 48 weeks of treatment, and both liver and spleen volume decreased (Muenzer et al., Mol Genet Metab, 2007). [3]
Antibodies to the drug are common but the treatment is generally well tolerated. Idursulfase antibodies were detected in 46.9% of patients in the larger trial, and infusion reactions did occur (Muenzer et al., Genet Med, 2006). [2]
Key Takeaways
Feature | Details |
Medical Name | Mucopolysaccharidosis Type II (MPS II). [1] |
Primary Cause | Mutation in the IDS gene; lack of the iduronate 2-sulfatase enzyme. [1] |
Inheritance | X-linked recessive (primarily affects males). [1] |
Core Symptoms | Stiff joints, coarse facial features, enlarged liver and spleen, and hearing loss. [1] |
Diagnosis | Urine tests (high GAGs), blood tests (low enzyme activity), and genetic testing. [1] |
Treatment | Enzyme replacement therapy (idursulfase), physical therapy, and symptom management. [1] |
What is Hunter syndrome (MPS II)?
Hunter syndrome is one of several lysosomal storage disorders categorized as mucopolysaccharidoses. [1] It is rare, occurring in approximately 1 out of every 100,000 to 170,000 male births. [1] The condition is divided into two types: severe (progresses rapidly with intellectual impairment) and mild (slower progression with normal intellectual development). [1] The severe type accounts for roughly 60% of all cases. [1]
What enzyme deficiency causes Hunter syndrome?
The root of Hunter syndrome lies in a genetic mutation of the IDS gene. This gene provides instructions for producing the enzyme iduronate 2-sulfatase (I2S).
The Role of Lysosomes
Lysosomes are specialized structures within cells that act as recycling centers. They use enzymes to break down large molecules like glycosaminoglycans (GAGs). In individuals with MPS II, the lack of the I2S enzyme prevents GAGs from being broken down, causing them to accumulate and eventually disrupt the cell's function. [1]
What are the signs and symptoms of Hunter syndrome (MPS II)?
Symptoms usually become noticeable between the ages of 2 and 4. [1] Because the damage is progressive, the physical changes become more pronounced over time.
Physical Characteristics
Facial features: Thickening of the nostrils, lips, and tongue (coarse features). [1]
Bone and joint: Stiff joints, short neck, wide chest, and a larger-than-normal head. [1]
Dental: Wide spaces between teeth and delayed tooth appearance. [1]
Organ enlargement: Enlarged liver (hepatomegaly) and spleen (splenomegaly). [1]
Skin: Distinctive white growths or bumps on the skin. [1]
Sensory and Developmental Changes
What complications are associated with Hunter syndrome?
Hunter syndrome complications can affect nearly every body system as GAGs build up, including the airways, heart, brain and nerves, joints and bones. [1]
How is Hunter syndrome diagnosed and screened for?
Early diagnosis is critical for starting treatments that can slow organ damage.
How is Hunter syndrome treated and managed?
Hunter syndrome has no cure yet, so treatment focuses on managing symptoms and slowing the disease's progression. [1]
Treatment | Purpose |
Enzyme Replacement Therapy (ERT) | |
Physical Therapy | To maintain joint mobility and improve function. [1] |
Surgical Interventions | To treat hernias, carpal tunnel, or blocked airways. |
Supportive Care | Hearing aids, respiratory support, and behavioral therapy. |
Clinical trials of gene therapy (gene editing) are underway and may provide future treatment options, but results are still awaited. [1]
What is the outlook and prognosis for Hunter syndrome?
Life expectancy with Hunter syndrome depends on the severity of the type, and people with the mild type often live into adulthood with proper management. [1]
A multidisciplinary team of specialists, including geneticists, cardiologists, and neurologists, is essential for providing comprehensive care.
Conclusion
Hunter syndrome is a complex and challenging condition that requires lifelong medical management. While the diagnosis is life-altering, advancements in enzyme replacement therapy have significantly improved the outlook and quality of life for many children. Early intervention and a strong support network are the foundations of effective care.
Frequently Asked Questions
Why does Hunter syndrome primarily affect boys?
Hunter syndrome is an X-linked recessive disorder. Since boys have only one X chromosome, a single faulty gene causes the disease. [1] Girls have two X chromosomes, so a healthy gene on the second chromosome usually protects them. [1]
Can girls ever get Hunter syndrome?
Hunter syndrome in girls is extremely rare, but possible if a girl inherits two faulty X chromosomes or has specific chromosomal issues. Typically, girls are "carriers" who can pass the gene to their children. [1]
What is the difference between Hunter and Hurler syndrome?
Hunter syndrome (MPS II) is caused by a lack of iduronate 2-sulfatase. Hurler syndrome (MPS I) is caused by a lack of alpha-L-iduronidase and is generally more severe.
How common is Hunter syndrome?
Hunter syndrome is very rare, affecting about 1 in 100,000 to 170,000 male births. [1]
What are glycosaminoglycans (GAGs)?
Glycosaminoglycans (GAGs) are complex sugar molecules that help build connective tissue, bone, and skin. In Hunter syndrome, they build up to toxic levels because they cannot be broken down. [1]
What was Hunter syndrome formerly called?
Hunter syndrome was previously known as gargoylism because of the coarse facial features, though this term is now considered outdated and insensitive.
Does enzyme replacement therapy (ERT) cure the disease?
No. ERT replaces the missing enzyme to help break down GAGs, which slows the damage, but it does not fix the underlying genetic mutation. [1]
Can ERT treat the brain symptoms?
Standard ERT does not easily cross the blood-brain barrier, so it is less effective at treating the cognitive decline seen in severe cases.
What are the first signs parents usually notice?
Frequent ear infections, hernias, and a change in facial appearance are often the earliest signs.
Is there a prenatal test for Hunter syndrome?
Yes. If the family history is known, genetic testing can be performed during pregnancy (amniocentesis or CVS).
Can Hunter syndrome cause seizures?
Yes. In severe cases, the buildup of sugars in the brain can lead to seizures. [1]
Why do children with Hunter syndrome have a large head?
The buildup of GAGs in the skull and brain tissues causes the head to grow larger than average (macrocephaly).
What is a "lysosomal storage disorder"?
A lysosomal storage disorder is a group of more than 50 rare inherited diseases where the cell's lysosomes fail to break down waste products, leading to cellular damage.
Does Hunter syndrome affect the heart?
Yes. GAGs often build up in heart valves, causing them to thicken and leak.
Can children with Hunter syndrome go to school?
Yes. Many children attend school with individualized education plans (IEPs) to accommodate physical or cognitive needs.
What is Elaprase?
Elaprase (idursulfase) is the brand name for the human-made enzyme used in replacement therapy.
How often is ERT administered?
Does Hunter syndrome cause pain?
Joint stiffness and carpal tunnel syndrome can cause significant discomfort, which is managed with therapy and medication.
Can Hunter syndrome cause hearing loss?
Yes. Progressive hearing loss is common in children with Hunter syndrome because of fluid buildup and nerve damage.
What is a genetic counselor?
A specialist who helps families understand the risks, inheritance patterns, and testing options for genetic disorders.
Are there support groups for Hunter syndrome?
Yes. Organizations like the National MPS Society provide resources and community for affected families.
Can Hunter syndrome cause behavioral problems?
In severe cases, children may exhibit hyperactivity, aggression, or a lack of danger awareness as brain function declines.
What is the "severe" vs. "mild" type?
The severe type involves cognitive decline and a shorter life expectancy; the mild type does not significantly affect intelligence. [1]
Does Hunter syndrome cause a short neck?
Yes. Skeletal abnormalities caused by GAG buildup often result in a shortened neck and wide chest. [1]
Can Hunter syndrome cause vision problems?
While less common than in other MPS types, some children may develop glaucoma or retinal degeneration.
What is hepatosplenomegaly?
Hepatosplenomegaly is the medical term for the enlargement of both the liver and the spleen, a common feature of Hunter syndrome. [1]
Can gene therapy fix Hunter syndrome?
Clinical trials are exploring ways to "edit" the DNA to produce the enzyme naturally, but this is not yet a standard treatment.
Does Hunter syndrome affect the lungs?
Yes. Thickened tissue in the throat and stiffening of the rib cage can make breathing difficult, especially during sleep (sleep apnea).
Can Hunter syndrome cause hernias?
Yes. Umbilical and inguinal hernias are very common in children with Hunter syndrome.
What is iduronate 2-sulfatase?
Iduronate 2-sulfatase is the specific enzyme that is missing or non-functional in people with Hunter syndrome. [1]
Is Hunter syndrome contagious?
No. It is a genetic condition inherited from parents; it cannot be caught like a cold or virus.
Can Hunter syndrome be detected at birth?
Some regions are beginning to include MPS II in newborn screening programs, allowing for very early detection.
Does Hunter syndrome cause skin changes?
Yes. Some children develop "pebbly" white skin growths, usually on the back, arms, or thighs.
Can Hunter syndrome affect the hands?
Yes. It often causes "claw hand" deformity and carpal tunnel syndrome.
What is the IDS gene?
The IDS gene is the gene located on the X chromosome that contains the instructions for making the I2S enzyme. [1]
Can carrier mothers have symptoms?
Most carrier females have no symptoms, though some may show very mild signs due to "X-inactivation."
Does Hunter syndrome affect height?
Yes. Growth usually slows significantly after age 5, leading to short stature in adulthood.
Can Hunter syndrome cause diarrhea?
Chronic diarrhea or loose stools are common in many children with MPS II.
What is a "storage" disease?
The term storage disease refers to the fact that the body "stores" waste products (GAGs) instead of getting rid of them.
How is the urine test performed?
A simple urine sample is analyzed for the presence and concentration of glycosaminoglycans.
Can Hunter syndrome cause sleep apnea?
Yes, due to narrowed airways and enlarged tonsils and adenoids.
What is the role of a cardiologist in Hunter syndrome?
To monitor heart valve function and heart muscle health through regular echocardiograms.
Can Hunter syndrome cause hydrocephalus?
In some cases, the buildup of GAGs can interfere with spinal fluid drainage, leading to "water on the brain."
Is the mild type really "mild"?
"Mild" is a relative term; individuals still face significant physical challenges, but their cognitive abilities remain intact.
Can ERT be done at home?
After the first few infusions in a clinic, some patients are eligible for home infusions administered by a nurse.
What is the life expectancy for the mild type?
Many individuals with the mild type live into adulthood, and some live into their 50s, 60s, or longer with modern care.
Can Hunter syndrome affect the spine?
Yes. It can cause spinal stenosis (narrowing of the spinal canal), which may require surgery to prevent nerve damage.
Does Hunter syndrome affect the teeth?
Yes. Wide spacing and late eruption are common [1], and specialized dental care is often needed.
What is the most important part of Hunter syndrome care?
Early diagnosis and a coordinated team of specialists to address the multi-system nature of the disease.
Where can I find clinical trials for Hunter syndrome?
Websites like ClinicalTrials.gov list ongoing research studies for new Hunter syndrome treatments.
Medical disclaimer: The information provided in this article is for educational purposes only and should not be considered medical advice. Always consult with a qualified healthcare professional for diagnosis and treatment of any health condition.
Source date: July 27, 2023. This article is current based on the most recent available data from the primary source.
Related Reading
Understanding Hurler Syndrome (MPS I): Symptoms, Causes, and Care explains MPS I, a closely related enzyme storage disorder.
Morquio Syndrome: Symptoms, Causes, and Management of MPS IV explains MPS IV, a related condition that mainly affects the skeleton.
Lysosomal Storage Diseases: Symptoms, Types, Causes, Diagnosis, and Treatment explains the larger group of inherited disorders that includes Hunter syndrome.
Carpal Tunnel Syndrome: Symptoms, Causes, Diagnosis and Treatment explains wrist nerve compression, a common problem in Hunter syndrome.
References
Cleveland Clinic. Hunter Syndrome (MPS II): Symptoms & Causes. Cleveland Clinic. Last updated July 27, 2023. https://my.clevelandclinic.org/health/diseases/17932-hunter-syndrome
Muenzer J, Wraith JE, Beck M, et al. A phase II/III clinical study of enzyme replacement therapy with idursulfase in mucopolysaccharidosis II (Hunter syndrome). Genet Med. 2006;8(8):465-73. PMID 16912578. https://doi.org/10.1097/01.gim.0000232477.37660.fb
Muenzer J, Gucsavas-Calikoglu M, McCandless SE, et al. A phase I/II clinical trial of enzyme replacement therapy in mucopolysaccharidosis II (Hunter syndrome). Mol Genet Metab. 2007;90(3):329-37. PMID 17185020. https://doi.org/10.1016/j.ymgme.2006.09.001
Comments