Mucopolysaccharidosis type IV (MPS IV) is a rare disease in which the body is missing or does not have enough of an enzyme needed to break down long chains of sugar molecules. These chains of molecules are called glycosaminoglycans (formerly called mucopolysaccharides). As a result, the molecules build up in different parts of the body and cause various health problems.
The condition belongs to a group of diseases called mucopolysaccharidoses (MPSs). MPS IV is also known as Morquio syndrome.
There are several other types of MPSs, including:
MPS IV is an inherited disorder. This means it is passed down through families. If both parents carry a nonworking copy of a gene related to this condition, each of their children has a 25% (1 in 4) chance of developing the disease. This is called an autosomal recessive trait.
There are two forms of MPS IV: type A and type B.
The body needs these enzymes to break down long strands of sugar molecules called keratan sulfate. In both types, abnormally large amounts of glycosaminoglycans build up in the body. This can damage organs.
Symptoms usually start between ages 1 and 3. They include:
The health care provider will perform a physical examination to check for symptoms that include:
Urine tests are usually done first. These tests may show extra mucopolysaccharides, but they can't determine the specific form of MPS.
Other tests may include:
For type A, the medicine called elosulfase alfa (Vimizim), which replaces the missing enzyme, may be tried. It is given through a vein (IV, intravenously). Talk to your provider for more information.
Enzyme replacement therapy is not available for type B.
For both types, symptoms are treated as they occur. A spinal fusion may prevent permanent spinal cord injury in people whose neck bones are underdeveloped.
These resources can provide more information about MPS IV:
Cognitive function (ability to think clearly) is usually normal in people with MPS IV.
Bone problems can lead to major health problems. For example, the small bones at the top of the neck may slip and damage the spinal cord, causing paralysis. Surgery to correct such problems should be done if possible.
Heart problems may lead to death.
These complications may occur:
Call your provider if symptoms of MPS IV occur.
Genetic counseling is recommended for couples who want to have children and who have a family history of MPS IV. Prenatal testing is available.
Reviewed By: Anna C. Edens Hurst, MD, MS, FACMG, Assistant Professor in Medical Genetics, The University of Alabama at Birmingham, Birmingham, AL. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.