MPS VI Maroteaux Lamy

Mucopolysaccharides are long chains of sugar molecules used in the building of bones, cartilage, skin, tendons and many other tissues in the body. “Muco” refers to the thick jelly-like consistency of the sugar molecules, “poly” means many, and “saccharide” is a general term for the sugar part of the molecule. In the course of normal life there is a continuous recycling process of building new mucopolysaccharides and breaking down old ones. The breakdown and recycling process requires a series of special biochemical tools called enzymes.

People with MPS VI are missing or are low in an enzyme called N-acetylgalactosamine-4-sulfatase, which is essential in breaking down mucopolysaccharides dermatan sulphate. When dermatan sulphate is not completely broken down it remains stored in the body. The symptoms of MPS VI occur when there is a build-up of dermatan sulphate in the tissues in the body. Babies may show little sign of the disease but as more and more cells build up with partially broken down dermatan sulphate, symptoms start to appear.

MPS VI is an autosomal recessive disease this means that both parents must carry the same affected gene and each pass this same affected gene to their child.

People probably carry from 5 to 10 genes with mutations in each of their cells. Problems happen when the particular gene is dominant or when a mutation is present in both copies of a recessive gene pair. Genes are the unique set of instructions inside our bodies that make each of us an individual. They are the blueprint for our growth and development, as well as controlling how our bodies function.

Genes are carried on structures called chromosomes and it is usual to have 23 pairs. A child will inherit half of the chromosomes from the mother and the other half from the father resulting in 23 pairs. 22 of these pairs look the same in both males and females. Pair 23 are the sex chromosomes, and this is the pair that differ between females and males. The X chromosome is inherited from the mother and the Y chromosome is inherited from the father. More information about inheritance is available in our publication.

For each pregnancy the chances of a baby inheriting MPS VI are completely independent of whether a previous child was affected with MPS VI. With each pregnancy there is a 1 in 4 chance that the baby will be affected by MPS VI.

All parents of children with MPS VI can benefit from genetic counselling, the counsellor can provide advice on the risk to close relatives and to suggest whether the wider family should be informed. To find out during a pregnancy, if the baby is affected by MPS VI, screening tests can be arranged early on during a pregnancy for those families who already have a child with MPS VI. Where only one parent is a carrier, they can opt for carrier screening but it is not 100% reliable or accurate and is not possible in all cases. Amniocentesis and chorionic villus sampling are both available during the pregnancy to find out if the baby is affected by MPS VI.

It might also be possible to have Pre-implantation genetic diagnosis (PGD) screening to avoid passing MPS VI to the baby. PGD is an assisted fertility treatment that involves checking the chromosomes of embryos before they are transferred in the womb using IVF techniques.

It is estimated that nearly 6% of the UK population (around 3.5million people) will be affected by a rare disease at some point in their lives. A single rare disease may affect up to about 30,000 people however the vast majority of rare diseases affect far fewer than that.

During a 10 year period (1989 to 1999), nine babies were born with MPS VI in the UK.

People with MPS VI can experience some or many symptoms from a wide spectrum which range from severe to very mild. MPS VI can be viewed as a continuous spectrum of the disease, with the most rapidly progressing people on one end and the more slowly progressing people on the other end, and a wide range of different severities in between.

Initial diagnosis is usually made between 6 and 24 months of age, and life expectancy depends on the severity of symptoms and is around 20 to 30 years. People with MPS VI often begin to show signs and symptoms of MPS VI during early childhood, these include changes to the physical appearance as well as developing other clinical features in the cardiovascular and respiratory systems.

Unlike other types of mucopolysaccharidosis, MPS VI does not affect intelligence.

For more on the symptoms, see:

• Appearance

• Dental

• Bones and joints

• Brain

• Ears

• Eyes

• Heart

• Liver, spleen and abdomen

• Lungs

Enzyme Replacement Therapy (ERT)

For people with MPS VI ERT is a long-term therapy whereby the missing or deficient enzyme is given via an intravenous infusion. The name for the replacement enzyme in MPS VI is galsulfase and the brand name is Naglazyme®. Naglazyme® was licensed as an ERT in 2006 in the EU and approved for use in MPS VI in the UK in 2005. The treatment has led to overall less physical deterioration leading to reduced disability, improving respiratory function and reducing joint stiffness.

Naglazyme ® is a weekly infusion lasting about 4 hours that can be administered at home. More information about Naglazyme® can be found at www.naglazyme.com and an EU version of the patient information leaflet is here.

For an up-to-date list of current UK based trials taking place visit Be Part of Research (resource provided by the National Institute for Health Research). For an international search visit Clinical Trials (resource provided by the U.S. National Library of Medicine).

This resource provides information on trial status including recruiting, completed or withdrawn and worldwide trial locations. To find out more about past or current trials speak to your doctor and learn about the risks and potential benefits.

The MPS Society is the only UK charity at the forefront of supporting people and families affected by MPS and related diseases. Our extensive support services offer you a wide range of support and resources.

The team can advise and sign post you to adequate needs-led support and services in your local area as well as social care, home adaptions, education and much more.

The support team can visit you in your home and provide you with vital support.

Get involved and support us in the community, volunteer or support fundraising; we are a small charity but with your support we can continue to offer a highly valued and essential service.