Definition

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 I (Hurler syndrome; Hurler-Scheie syndrome; Scheie syndrome)
• MPS II (Hunter syndrome)
• MPS III (Sanfilippo syndrome)

Alternative Names

MPS IV; Morquio syndrome; Mucopolysaccharidosis type IVA; MPS IVA; Galactosamine-6-sulfatase deficiency; Mucopolysaccharidosis type IVB; MPS IVB; Beta galactosidase deficiency; Lysosomal storage disease - mucopolysaccharidosis type IV

Causes

MPS IV is an inherited disorder. This means it is typically 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.

• Type A is caused by a defect in the GALNS gene. People with type A do not have an enzyme called N-acetylgalactosamine-6-sulfatase.
• Type B is caused by a defect in the GLB1 gene. People with type B do not produce enough of an enzyme called beta-galactosidase.

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 bodily organs.

Symptoms

Symptoms usually start between ages 1 and 3 years. They include:

• Abnormal development of bones, including the spine
• Bell-shaped chest with ribs flared out at the bottom
• Cloudy cornea
• Coarse facial features
• Enlarged liver
• Heart murmur
• Hernia in the groin
• Hypermobile joints
• Knock-knees
• Large head
• Loss of nerve function below the neck
• Short stature with a particularly short trunk
• Widely spaced teeth

Exams and Tests

Your health care provider will perform a physical exam that may find:

• Abnormal curvature of the spine
• Cloudy cornea
• Heart murmur
• Hernia in the groin
• Enlarged liver
• Loss of nerve function below the neck
• Short stature (especially short trunk)

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:

• Blood enzyme levels
• Echocardiogram
• Genetic testing
• Hearing test
• Slit-lamp eye exam
• Skin fibroblast culture
• X-rays of the long bones, ribs, and spine
• MRI of the lower skull and upper neck

Treatment

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.

Support Groups

More information and support for people with MPS IV and their families can be found at:

• National MPS Society -- mpssociety.org/
• National Organization for Rare Disorders -- rarediseases.org/gard-rare-disease/mucopolysaccharidosis-type-iv/
• NIH Genetic and Rare Diseases Information Center -- rarediseases.info.nih.gov/diseases/12562/mucopolysaccharidosis-type-iv

Outlook (Prognosis)

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.

Possible Complications

These complications may occur:

• Breathing problems
• Heart failure
• Spinal cord damage and possible paralysis
• Vision problems
• Walking problems related to abnormal curvature of the spine and other bone problems

When to Contact a Medical Professional

Contact your provider if symptoms of MPS IV occur.

Prevention

Genetic counseling is recommended for couples who want to have children and who have a family history of MPS IV. Prenatal testing is available.

References

Pyeritz RE. Inherited diseases of connective tissue. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 239.

Spranger JW. Mucopolysaccharidoses. In: Kliegman RM, St. Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM, eds. Nelson Textbook of Pediatrics. 21st ed. Philadelphia, PA: Elsevier; 2020:chap 107.

Turnpenny PD, Ellard S, Cleaver R. Inborn errors of metabolism. In: Turnpenny PD, Ellard S, Cleaver R, eds. Emery's Elements of Medical Genetics and Genomics. 16th ed. Philadelphia, PA: Elsevier; 2022:chap 18.