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In the United States, an orphan or rare disease occurs in less than 200,000 individuals. Also, there are some diseases that only affect that many individuals in the entire world. Than there are those diseases that are widespread in certain parts of the world but are rare in others. And there are some diseases that are truly one-of-a kind, usually due to a genetic defect. The United States Office of Rare Diseases (USORD) list over 6,000 diseases considered rare in the United States; Hunter Syndrome is one of those diseases.

Historical Background: The National Mucopolysaccharide Society (MPS) described Hunter Syndrome as a mucopolysaccharide (muco-poly-saccharide) storage disorder that is also called Mucopolysaccharidosis II (MPS II).

Hunter Syndrome is named after Charles Hunter, a professor of medicine of Manitoba, Canada, who first described two brothers with the disorder in 1917. Two types of Hunter Syndrome have been identified, mild and severe. However, there are individuals with intermediate severity who do not fit neatly in either the severe or the mild forms of the disease. Studies have clearly shown that current understanding of the enzyme and its gene demonstrated that MPS II comprises a broad spectrum of severity that individuals may be diagnosed from severe to mild Hunter with many individuals falling somewhere in between.

Researchers concluded that all individuals with Hunter Syndrome have a deficiency of the enzyme iduronate sulfatase, which results in the build up of mucopolysaccharides, more recently called glycos-amino-glycans (GAG). The accumulation of GAG is responsible for the many problems that affect individuals with MPS II.

So far, there is no cure for individuals affected with these disorders. However, there are means to manage the challenges that the individuals will experience, and assist them to live a productive life. Several treatments had been tried with limited success. Such as bone marrow transplantation with poor results. Currently, enzyme replacement therapy is being studied, which may help some individuals affected with MPS II. Researchers continue to look for more effective method to treat these disorders, and hopefully those affected will have more and better options available in the near future.

Even with stem cell transplant or enzyme replacement therapy, individuals with MPS II continue to have significant muscular and skeletal disabilities, more commonly involving the spine, hips, knees, and hands. These are rarely life-threatening, but frequently limit the individual function, activity, and quality of life issues. Surgical intervention is often required to optimize long-term function. The timing and type of surgical intervention may vary among individuals and surgeons. Still, early evaluation is important in determining proper treatment, and to optimize quality of life for those affected with MPS II.

How Hunter Syndrome is Inherited: Hunter Syndrome has a different form of inheritance from all other MPS disorders. Hunter Syndrome is a sex-linked disorder, meaning that it is transmitted on the female X-chromosome from mother to her children. In which case, the syndrome is most often seen in males. However, rare female cases have been reported. Hunter Syndrome can occur in any ethnic group; but a higher incidence has been reported in the Jewish population living in Israel. Hunter Syndrome may occur as frequently as one individual per 65, 000 births to as rarely as one individual in 132, 000 births.

As stated above, girls may be the carriers of the disease but except in the rare case, only boys will be affected. For example, if a woman is the carrier for MPS II disorder, there is a 50% risk that any male child born to her will be a carrier for the disease. It is very important to remember that not all women with only one MPS II child will be carriers of the abnormal gene. For instance, if only one individual in a family has MPS II, the carrier status of the birth mother cannot be definitavely determined. However, if additional affected individuals are known, than the mother of an MPS II child is assumed to be a carrier.

The sisters and maternal aunts of a person with Hunter Syndrome may also be carrier of the disorder and would have a 50% chance of passing the abnormal gene to a son. It is strongly suggested that all families of individuals with Hunter Syndrome should seek consultation from their medical genetic doctor or a genetic counselor before planning to have additional children. It should be noted that analysis of enzyme level, in itself, is not a reliable method to determine MPS II carrier status for many individuals.

What Causes MPS Disorders? Mucopolysaccharides are a long chains of sugar molecules used in the construction of bones, cartilage, skin, tendons, and many other tissues in the body. They form part of the structure of the body and also give the body many of the special features that make it work. For example, the slippery joint fluid that lubricates your joints contains mucopolysaccharides. The rubbery resilient cartilage in your joints is another good example. All bodily tissues have some of the substance as a normal part of their structure.

The modern word for mucopolysaccharides is glycos-amino-glycans or (GAG), which stands for sugar-amino-sugar polymer or long repeating sugar chains found in these materials. These sugar chains are submicroscopic and cannot be seen with the naked eyes, but can be studied using special scientific instruments and analytical methods.

To understand how GAG accumulate and cause MPS II, it is important to know that in the course of normal life, there is continuous process of constructing new mucopolysaccharides and breaking down old ones; a recycling process. Interesting enough, this ongoing process is necessary to keep your body healthy. This process of break down and recycling requires a series of special biochemical tools called enzyme. In order to successful break down GAG, a series of enzymes or tools work in sequence one after another to split the GAG into pieces. Each enzyme in the process has its special purpose in the body and does just one special function; like a screwdriver works on screws and a hammer works on nails.

According to several studies individuals with MPS II are missing one specific enzyme called iduronate sulfatase, which is essential in the process to break down certain GAG called dermatan sulfate and heparin sulfate. The incompletely broken down dermatan sulfate and heparin sulfate remain stored inside cells in the body and begin to build up, causing progressive damage. GAG itself is not toxic but the amount of it and the effect of storing it in the body leads to multiple physical problems. Babies may show little sign of the disorder, but as more and more GAG accumulates symptoms begin to appear. Sugar or other foods normally eaten will not affect weather there is more or less build up of GAG.

Individuals diagnosed with Hunter Syndrome almost always have neurocognitive degeneration with progressive and profound mental retardation. When the diagnosis is made in children younger than three years old a progressively severe decline in intellectual functions occurs. Children with MPS II typically have the skeletal changes referred to as dysostosis multiplex. These individuals also exhibits progressive coarsening of facial features, short stature, joint stiffness, hepatosplenomegaly, and hernias as common presenting signs and symptoms. info@mpssociety.org

Individuals inflicted with MPS II may have popular skin lesions that are ivory in color and located on the upper back and the lateral upper arms and thighs. Other skin lesions are hypertrichosis and thickened skin. And extensive Mongolian spots associated with Hunter Syndrome have also been reported. These individuals tend to have severe mental retardation and deafness. Other symptoms include cerebral ventricular dilation. The facial features of Hunter Syndrome are coarse, but the children still have faces that resemble other family members.

Mildly affected children may behave in a normal manner and they can be quite affectionate with a sunny nature. On the other hand, they can become short-tempered when frustration sets-in due to physical limitations which often make life very difficult. Children who are mildly affected with MPS II should be encouraged to be as independent as they can; since many adults with Hunter Syndrome lead a relatively normal and enjoyable life.

According to one study done by the National MPS Society, many mildly affected Hunter adults have found productive employment as a teacher of the deaf, a marine architect, and another a sergeant in the army. info@mpssociety.org As for education, it is suggested, that some MPS II children could benifit from having a mainstreamed education enjoying the social interaction with peers. However, it is very important that parents and caretakers work closely with professional educators in the school system and develop the best Individualized Education Program (IEP) for children with Hunter Syndrome and other rare diseases.

Finally, I believe that families, caregivers, and educators should go the extra mile to educate themselves about Hunter Syndrome and other rare debilitating diseases that inflict children at such an early age. However, too often, any developed thirst for knowledge in this area may be left unsatisfied due to the lack of information about these diseases available to the public. Nevertheless, this barrier can be overcome with the advancement in technology and more people are introduced to the Internet.

Dr William Smith is a psychologist and consultant with many years experience working with individuals and groups. Dr Smith specializes in working with Adult Children of Alcoholics, and Survivors of Sexual Trauma such as Rape and Incest. For further information visit my website at: http://insightconsultant.com
For additional information on Hunter Syndrome go to info@mpssociety.org