What is MPS II?
What Is MPS II (Hunter Syndrome)?
According to National MPS Society, Hunter Syndrome, also referred to as Mucopolysaccharidosis type II or MPS II, is a progressively degenerative genetic disease that almost exclusively affects males. Boys with MPS II are deficient in the enzyme iduronate-2-sulfatase that helps breakdown glycosaminoglycans (GAG). The net result is that GAG builds up in cells and organs throughout the body. Because this chemical decomposition is unable to happen, these cells continuously accumulate to toxic levels and build up can lead to a fairly uniform plethora of symptoms and can begin around 2-5 years of age. These symptoms include stunted growth, coarse facial features, stiff joints, intellectual disability, serious physical deformities, significant damage to the brain & organ function and eventually leads to premature death. The severe form often includes progressive cognitive impairment and a life span of approximately 12-15 years old. Currently, there is no cure for individuals affected by this disease, which is why funding to bring the research by geneticists to the first phase of human clinical trials is so crucial. Today, the only treatment available for MPS II is enzyme replacement therapy (ERT). ERT for MPS II was approved by the FDA in 2006 and is known as Elaprase®. Elaprase® is a manufactured version of the body’s natural iduronate sulfatase enzyme. It does not cross the blood-brain barrier at normal doses and thus is not anticipated to have an impact on any neurocognitive decline occurring in individuals with MPS II. Treatments of Elaprase® are given weekly through intravenous infusions. Scientists and geneticists who study MPS II continue to look for better and more effective ways to treat this disease and ultimately hope for a cure.
What Causes MPS II (Hunter Syndrome)?
Mucopolysaccharides are long chains of sugar molecule used in the building of connective tissues in the body.
- “saccharide” is a general term for a sugar molecule (think of saccharin)
- “poly” means many
- “muco” refers to the thick jelly-like consistency of the molecules
There is a continuous process in the body of replacing used materials and breaking them down for disposal. Children with MPS II are missing an enzyme called iduronate sulfatase, which is essential in cutting up the mucopolysaccharides called dermatan and heparan sulphate. The incomplete broken down mucopolysaccharides remain stored in cells in the body causing progressive damage. Babies may show little sign of the disease, but as more and more cells become damaged, symptoms start to appear.
How common is MPS II (Hunter Syndrome)?
This is a rare condition affecting 1 in 100,000 to 1 in 150,000 males. There is an estimate in the United States that 1 in 25,000 births will result in some form of MPS.
How is the disease inherited?
MPS II occurs in boys, and girls may be carriers of the gene for MPS II. Although rare, MPS II has been diagnosed in girls. All families of children with MPS II should seek further information from their doctor or genetic counselor before planning to have more children. If the mother is a carrier, there is a 50% risk that any boy born will have the disease. The sisters and maternal aunts of a person with MPS II may be carriers of the disease and would also have a 50% chance of passing the syndrome to a son. There are tests available for carriers, so it is important for all female relatives on the mother’s side to seek advice from their doctor.
What are the Signs and Symptoms of Hunter Syndrome?
Symptoms usually develop at 2 to 5 years of age and can include the following:
- Stunted growth
- A bloated or inflated abdomen
- Coarse facial features (large forehead, thick neck, tongue & lips, bushy eyebrows, flattened nose, chubby rosy cheeks)
- Intelligence impaired in more severe forms
- Cognitive delays such as late walking talking and recognition
- Hearing loss
- Joint stiffness
- Carpal tunnel syndrome
- Sleep apnea
- Poor peripheral vision
- Thickening of the heart valves
- Obstructive airway disease
- Frequent coughs, colds and infections
- Enlarged liver and spleen
- Missing an essential enzyme necessary for breaking down sugars in the body
Early diagnosis of MPS II is crucial for a child’s life. The earlier MPS II is diagnosed, the sooner potential treatment options can be explored and supportive care may be started to potentially prevent some of the permanent damage that may be caused by the disease. To diagnose MPS II, the doctor will typically first do a urine test to look for levels of GAG that are higher than normal. The results are compared to levels of GAG that are known to be normal for various ages. Most, but not all, individuals with MPS have GAG levels in their urine that are higher than those of individuals without MPS. A urine test is only one of the first steps in diagnosing MPS II; a clear diagnosis requires a test to measure levels of enzyme activity in the blood or skin cells. In healthy individuals, the tests show white blood cells, serum and skin cells that contain normal levels of enzyme activity. In individuals with MPS II, the enzyme activity levels are much lower or absent.
Is There A Cure For Hunter Syndrome?
Currently there is no definitive cure for Hunter Syndrome. Geneticists have completed critical research that leads them to believe they may possibly be close to a cure for MPS II. However, funding is ultimately the only barrier holding geneticists back from moving to the first phase of human clinical trials. Therefore, the only thing currently available to children suffering from MPS II is the first FDA approved enzyme replacement therapy (ERT) known as Elaprase® (idursulfase). This is the only treatment currently approved for Hunter syndrome in the United States. It replaces the protein their body doesn’t make. Elaprase® is administered into the body through an IV. This is a long, painful, weekly process that carries with it significant risks of adverse reactions, including anaphylactic shock. Elaprase® does not cross the blood brain barrier so it cannot help any damage Hunter Syndrome does to the brain. There are currently no treatment options that help improve brain and mental health. For more information on the treatment, visit http://www.elaprase.com/
U.S. National Library of Medicine. Genetics Home Reference
National Organization for Rare Disorders