MPS IVA and MPS IVB – Morquio disease
For more information please download our Guide to MPS IV.
What is MPS IV?
Morquio Disease is a Mucopolysaccharide storage disorder also known as MPS IV. The disease takes its name from Dr Morquio, a paediatrician in Uruguay, who described a family of four children affected by the condition in 1929.
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
In the course of normal life there is a continuous recycling process of building new Mucopolysaccharides and breaking down old ones. This process requires a series of biochemical tools called enzymes. Children and adults with Morquio Disease are missing an enzyme which is essential in the breaking down of Keratan Sulphate.
Incompletely broken down Keratan Sulphate remains stored inside parts of cells called lysosomes. The lysosomes become swollen and disrupt cell function causing progressive damage.
Babies may show little sign of the disease but symptoms start to appear as more and more cells become damaged by the accumulation of Mucopolysaccharides.
Does Morquio affect individuals differently?
There are two types of Morquio Disease which are referred to as MPS IVA and MPS IVB. The subtypes of this disease are as a result of the type of enzyme that is missing or malfunctioning within the cells of the body: A missing or malfunctioning enzyme known as ‘N-acetylgalactosamine 6-sulfatase’ results in MPS IVA. In MPS IVB the missing or malfunctioning enzyme is known as ‘beta-galactosidase’.
Morquio Disease comprises a wide spectrum of severity and clinical involvement. Some individuals may not achieve a height of one metre by adulthood, whilst others grow significantly taller and have fewer problems related to severely restricted growth.
How common are these diseases?
The MPS Society, which co-ordinates the Registry for Mucopolysaccharide and Related Diseases, has shown that Morquio Disease is a rare condition, for example: between 1989 and 1999, 26 babies were born with Morquio Disease in the UK.
How is the disease inherited?
Morquio Disease is an autosomal recessive disease whereby both parents must carry the same defective gene and each pass this same defective gene to their child. Where both parents are carriers of the MPS IV gene there is a 25% (1:4) chance of having an affected child in each pregnancy. There is a 50% (1:2) chance of a child receiving only one copy of the defective gene and therefore being a carrier. A carrier will not be affected but can pass the defective gene to his or her offspring. The remaining 25% (1:4) will be neither affected nor a carrier. Using information from an affected individual’s DNA it may be possible to determine whether brothers and sisters are carriers of, or are affected.
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.