MPS II – Hunter
For more information please download our Guide to MPS II.
What is MPS II?
Hunter Disease is a Mucopolysaccharide storage disorder also known as Mucopolysaccharidosis Type II (MPS II). Hunter Disease takes its name from Charles Hunter, a Professor of Medicine in Manitoba, Canada, who first described two brothers with the disorder in 1917.
In the past, just two types of Hunter Disease have been described, mild and severe. It is now clear, however, based on current understanding of the enzyme and its gene, that Hunter Disease comprises a wide spectrum of severity.
All individuals with MPS II have a deficiency of the enzyme ‘iduronate sulphatase’ which results in the accumulation of Mucopolysaccharides. The accumulation of Mucopolysaccharides is responsible for many problems that affect individuals with MPS II.
Although there is no cure for MPS diseases, there are ways of managing and treating the problems they cause.
What causes this disease?
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
Individuals with MPS II are missing, or are deficient in, an enzyme called ‘iduronate sulphatase’ which is essential in the breaking down of the Mucopolysaccharides called ‘dermatan’ and ‘heparan sulphate’.
The incompletely 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.
Does MPS II affect individuals differently?
Until recently MPS II had been described as either mild or severe. However, based on current understanding of the enzyme and its gene, MPS II comprises a wide spectrum of severity. Some individuals will have progressive developmental delay and severe progressive physical problems. Others will have normal intelligence and progressive physical problems, some being more severely affected than others.
It is important to remember that MPS II is extremely varied in its effects.
How common is MPS II?
Except in very rare cases, only males will be affected by MPS II. The MPS Society, which co-ordinates the European Registry for Mucopolysaccharide and related diseases, has shown that this is a rare condition affecting 1 in 100,000 male births. Over a 10 year period, between 1992 and 2002, 52 babies with MPS II were born in the UK.
How is the disease inherited?
MPS II has a different form of inheritance from all other MPS Diseases as it is an X-linked recessive disease (also called sex-linked) like haemophilia.
Females may be carriers, but except in very rare cases only males will be affected. If a woman is a carrier for MPS II there is a 50% (1:2) risk that any male born to her will have the disorder. Furthermore, there is a 50% (1:2) risk that any female born to her will be a carrier for the disorder. This means that there is a 25% (1:4) chance of having an affected child with each pregnancy.
The sisters and maternal aunts of an individual with MPS II may be carriers of the disorder and would also have a 50% risk of passing the abnormal gene to any male born to them. In many families it is possible to detect female carriers by direct analysis of genetic material. The doctor may wish to take a sample of blood from your affected child so that the exact genetic abnormality can be detected. In most families it is possible to identify the exact genetic fault on the X-chromosome responsible for MPS II (mutation analysis).
This can help with pre-natal diagnosis and carrier testing. However, the mother is not always found to be a carrier for MPS II in all cases. In this situation the disorder may have occurred in the male for the first time, a new mutation.
There is a more detailed explanation of this complex subject in the booklet on inheritance available from the MPS Society.
For available treatment options and the latest news and information on research, therapies and clinical trials please visit our treatment section.