MPS IV – Morquio Disease

Elena McGauran

Morquio disease is one of the mucopolysaccharide diseases also known as MPS lV. It takes its name from Dr. Morquio, a paediatrician in Montevideo, Uruguay, who in 1929 described a family of four children affected by the condition.

What causes this disease?

There is a continuous process in the body of replacing used materials and breaking them down for disposal. Children with Morquio disease are missing an enzyme which is essential in cutting up the mucopolysaccharide called keratan sulphate. The incompletely broken down mucopolysaccharides cannot be used in the proper development of bones and cartilage and 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.

The usual form of Morquio disease is known as MPS lVA to distinguish it from the much rarer B form which is caused by the lack of a different enzyme. Sufferers from the B form have similar problems, but tend to be less severely affected.

How is the disease inherited ?

We 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. Morquio disease is caused by a recessive gene. 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 suffer the disease.

There is a two in three chance that unaffected brothers and sisters of Morquio sufferers will be carriers. They can be reassured however that, as the disease is so rare, the chance of having a partner who is another carrier is very slight provided their partner is not a cousin or other close family member.