The MPS Diseases

The Mucopolysaccharidoses (MPSs) are rare genetic disorders in children and adults. They involve an abnormal storage of mucopolysaccharides, caused by the absence of a specific enzyme. Without the enzyme, the breakdown process of mucopolysaccharides is incomplete. Partially broken down mucopolysaccharides accumulate in the body’s cells causing progressive damage. The storage process can affect appearance, development and the function of various organs of the body.  Each MPS disease is caused by the deficiency of a specific enzyme.

Lysosomal Storage Disorders

The MPS diseases are part of a larger group of disorders known as Lysosomal Storage Disorders (LSDs).  The combined incidence of LSDs in the population is 1 in 5,000 live births.  Each of the more than 40 individual LSDs result in a deficiency in the activity of a specific protein (enzyme) which is normally present in each of the billions of cells that make up our bodies.

The role of lysosomes is to degrade waste material made by these cells into simpler products for re-use.  This process of waste removal requires the sequential action of a number of enzymes. If one of these enzymes is present in insufficient amounts, the recycling process cannot proceed and the undegraded material remains stored within the lysosome and, therefore, the cell. As the amount of stored material increases over time, normal cellular functioning becomes increasingly impaired, leading to the emergence of clinical symptoms.

Other diseases similar to MPS include the Mucolipidoses, Oligosaccharidoses and Glycosphingolipidoses. The Australian MPS Society includes these and other disorders as part of its "related diseases" and aims to extend its support and assistance to families affected by these disorders.

Babies may show little sign of the disorder, but as more and more cells become damaged, symptoms start to appear. Although there are similarities between all the MPS Diseases, each of the individual diseases will result in different effects on the body.

Inheritance

inheritance recWe all have genes inherited from our parents which control whether we are tall, short, fair, etc. Some genes we inherit are "recessive", that is to say we carry the gene but it does not have any effect on our development. 

Apart from MPS II or Hunter Syndrome, the MPS diseases are caused by a recessive gene. In most cases, if an adult carrying the abnormal gene marries another carrier there will be a one in four chance with every pregnancy that the child will inherit the defective gene from each parent and will be affected with the disorder. There is a two in three chance that unaffected brothers and sisters of MPS children will be carriers. They can be reassured however that, as the disorder is so rare, the chance of marrying another carrier is very slight provided they do not marry a cousin or other close family member. 

Hunter syndrome has a different form of inheritance from the other MPS diseases as it is "sex-linked" like haemophilia. Girls may be carriers of the disease but, except in very rare cases, only males will be sufferers. Hunter adults have been known to marry. Their children are unaffected. However, daughters of a Hunter father will be carriers of the disorder.

Prenatal Diagnosis

If you already have a child with an MPS disorder it is possible to have tests during a subsequent pregnancy to find out whether the baby you are carrying is affected. Prenatal diagnosis is possible through amniocentesis and chorionic villus samples. If you are planning a further pregnancy it is important to consult your doctor or genetic counsellor so that tests can be performed and preparations made for diagnosis early in the pregnancy.

Once the gene has been identified in a family other family members may feel it advisable to consult a genetic counsellor before having children.

Australian research estimates that 1 in 22,465 births will result in some form of MPS.