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Understanding Hunter Syndrome (MPS II): Causes, Symptoms, Diagnosis, and Treatment

Jerome Albert Ecker | MD

Medically reviewed by Jerome Albert Ecker | MD, Assistant Professor of Medicine, Duke University - Durham, NC on July 24th, 2023.

Key Takeaways

  • Deficiency of iduronate-2-sulfatase enzyme causes mucopolysaccharides to accumulate in lysosomes, progressively damaging heart, liver, spleen, and airways over time.

  • Two distinct forms exist: severe type with neurological involvement appearing by age 2-4, and mild type with normal intelligence but joint and organ problems developing in childhood.

  • Characteristic coarse facial features develop gradually—enlarged skull, thick lips, broad nose, and protruding tongue—often becoming more pronounced with age.

  • Enzyme replacement therapy (idursulfase) given intravenously every week can reduce liver/spleen size and improve walking capacity, but cannot cross the blood-brain barrier to treat cognitive symptoms.

  • Urine glycosaminoglycan levels and enzyme activity testing in blood or skin cells provide definitive diagnosis, with genetic testing recommended for family planning.

Hunter syndrome, also known as mucopolysaccharidosis II or MPS II, is a rare genetic disorder that primarily affects boys. It occurs when the body cannot break down certain sugars that build bones, skin, tendons, and other tissues. As a result, these sugars accumulate in the cells, causing damage to various parts of the body, including the brain.

Causes of Hunter Syndrome

Hunter syndrome is caused by a problem with a specific gene that boys inherit from their mothers. This gene is responsible for producing an enzyme that breaks down the sugars. When the gene is defective, the enzyme is not produced, leading to the accumulation of sugars in the body.

Symptoms of Hunter Syndrome

The symptoms of Hunter syndrome can vary from person to person, but some common signs include:

  • Distinctive facial features (large, round cheeks, broad nose, thick lips, and a large tongue)

  • Joint problems and stiffness

  • Frequent respiratory infections

  • Hearing loss and ear infections

  • Difficulty walking and muscle weakness

  • Enlarged liver and spleen

  • Heart valve problems

  • Developmental delays and learning difficulties (in severe cases)

Understanding Hunter Syndrome (MPS II): Causes, Symptoms, Diagnosis, and Treatment

Diagnosing Hunter Syndrome

Diagnosing Hunter syndrome involves ruling out other medical conditions and conducting specific tests, such as:

  • Urine tests to check for high levels of certain sugars

  • Blood or skin cell tests to measure the activity of the missing enzyme

  • Genetic testing to identify the abnormal gene

If you have a family history of Hunter syndrome or another genetic disorder, it's essential to inform your doctor. Pregnant women who carry the gene or have a child with Hunter syndrome can undergo prenatal testing to determine if their unborn child is affected.

Treatment Options for Hunter Syndrome

While there is no cure for Hunter syndrome, early treatment can help slow the progression of the disease and manage symptoms. Some treatment options include:

Enzyme Replacement Therapy (ERT)

ERT involves replacing the missing enzyme through regular infusions. This treatment can help improve walking, joint movement, breathing, and growth in boys with milder forms of Hunter syndrome. However, it does not effectively treat brain-related symptoms.

Bone Marrow and Umbilical Cord Blood Transplants

These transplants introduce cells that can produce the missing enzyme into the body. However, they are high-risk procedures and are not commonly used due to limited effectiveness in treating brain-related symptoms.

Symptom Management

Various specialists, such as cardiologists, ENTs, eye doctors, and neurologists, can help manage the specific symptoms of Hunter syndrome. Physical and occupational therapy can improve joint mobility and daily functioning, while medications may help with sleep issues.

Living with Hunter Syndrome

Caring for a child with Hunter syndrome requires a supportive and proactive approach. Encourage your child to participate in family activities, maintain friendships, and learn as much as possible while their brain function allows. Work with schools to develop an individualized education program (IEP) and seek support from organizations like the National MPS Society to connect with other families facing similar challenges.

Remember, every child with Hunter syndrome is unique, and their experiences may differ. By staying informed, working with healthcare professionals, and providing a loving and supportive environment, you can help your child live a meaningful and fulfilling life.

Additional Resources

The Bottom Line

Early enzyme replacement therapy starting before age 6 offers the best outcomes for preserving mobility and organ function in this progressive X-linked disorder. Families benefit from genetic counseling since carrier mothers have a 50% chance of passing the defective gene to each child. If you're concerned about developmental delays or distinctive facial features in a young boy, Doctronic can help connect you with appropriate genetic testing and specialist care.

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