Children's Hospital of Orange County

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Mucopolysaccharidosis (MPS)

What is mucopolysaccharidosis (MPS)?

The mucopolysaccharidoses (MPSs) are a group of related lysosomal storage diseases. Lysosomes are compartments in cells that break down molecules and remove waste products from cells. Normally, different enzymes in the lysosomes break down complex sugars called glycosaminoglycans, also known as mucopolysaccharides. In MPS, glycosaminoglycans are not broken down because of a deficiency in one of those lysosomal enzymes. As a result, the glycosaminoglycans accumulate in the cells and cause tissue damage.

Different types of MPS are classified by the enzymes that are absent or deficient. To date, seven types of MPS have been reported: MPS I, II, III, IV, VI, VII and IX.

All types of MPS are inherited and share very similar physical symptoms. The physical symptoms may include thickening of lips and skin, enlarged liver and spleen, hernias, recurrent ear infections requiring ear tube placement, joint pain and stiffness, and short stature. Neurological symptoms are present in some types of MPS and may vary in severity.

It is estimated that in the United States, one in 25,000 births are affected by some form of MPS. MPS III, also called Sanfilippo syndrome, is one of the more common types, while MPS VII is very rare. Lifespan of a patient with MPS varies depending on the severity and type of disease but it is possible for a person with a mild form of MPS to live into adulthood.

There is currently no known cure for MPS. Therapies that aim to replace the deficient enzymes may help improve upper airway problems, reduce liver and spleen enlargement and improve overall well-being. Other aspects of treatment aim to relieve and manage symptoms in order to improve and prolong life. Sometimes, physical therapy or orthopaedic surgery is required for correcting skeletal abnormalities.

What are the signs and symptoms of MPS?

Each type of MPS has different symptoms and has varying degrees of severity. All types have a period of normal growth that is followed by a decline in physical and mental functioning.

Common physical symptoms include:

  • Thickened lips and skin
  • An enlarged tongue
  • Enlarged organs, specifically the liver and spleen
  • Recurrent ear or sinus infections
  • Inguinal and/or umbilical hernias
  • Abnormal bone size and shape
  • Joint pain and stiffness
  • Corneal clouding
  • Short stature.

Neurological symptoms may occur in some types of MPS. They may include:

  • Decreased intellectual capacity
  • Hyperactivity
  • Insomnia
  • Delirium
  • Aggressive behavior
  • Loss of previously acquired developmental milestones.

Effects on breathing function may include:

  • Sleep apnea
  • Obstructive airway disease
  • Chronic respiratory infections
  • Enlarged tonsils and adenoids
  • Noisy and difficult breathing.

Heart abnormalities may be more common in some types of MPS than others. These abnormalities may include:

  • Valve defects
  • Thickening and stiffening of the heart wall
  • Narrowing of blood vessels.

At our MPS Multidisciplinary Center, we have a team of pediatric specialists from multiple fields to treat any of the symptoms that may occur because of MPS.

How is MPS diagnosed?

MPS may be suspected after a thorough physical examination if your physician notices the different symptoms and findings that are characteristic of MPS. An elevated level of glycosaminoglycans may also be detected in the urine, suggesting the possibility of mucopolysaccharidosis.

If MPS is suspected, measurement of lysosomal enzymes and DNA testing are then performed to identify the specific type of MPS.

What are the complications of MPS?

Patients should be continually followed by their physician to be assessed for declining physical and mental functioning. Depending on the type of mucopolysaccharidosis (MPS), patients may need to be evaluated more often than others due to differences in disease progression and severity.

Neurologic: Certain types of MPS result in cognitive disabilities. Narrowing or compression of spinal nerves may result in weakness and changes in sensation of the arms and legs.

Cardiovascular: Common heart abnormalities may include valve defects, thickening and stiffening of the heart wall, and narrowing of blood vessels. Complications of heart abnormalities are cardiovascular collapse and death if not corrected. Surgery and prescription medications may be useful in preventing complications.

Respiratory: Effects on breathing function include sleep apnea, obstructive airway disease, chronic respiratory infection, enlarged tonsils and adenoids, and noisy and difficult breathing. Chronic respiratory infections can lead to pneumonia, which can be life-threatening if untreated. Enlarged adenoids and tonsils may contribute to difficulty breathing and sleep apnea.

Skeletal: Abnormal bone and cartilage formation result in joint pain, stiffness, and decreased mobility and quality of life. Bone abnormalities may compress nerves, leading to inhibition of normal neurological function.

Endocrinology: Short stature, growth hormone and other hormonal deficiencies, and reduced bone mineral density are very common in patients with MPS.

At our MPS Multidisciplinary Center, we have a team of pediatric specialists from multiple fields to treat any of the symptoms that may occur because of MPS.

How is MPS treated?

Currently, there is no known cure for any form of mucopolysaccharidosis (MPS), but there are treatments available to manage symptoms, prevent complications and improve quality of life. Physical therapy may be helpful in the prevention and treatment of joint pain and stiffness that is common in all types of MPS.

Hematopoietic cell transplantation: The use of hematopoietic cell transplantation may be beneficial when performed at an early age in MPS I, providing cells that produce the missing enzymes. The use of early hematopoietic cell transplantation may help to prevent neurodegeneration and improve other symptoms, but does not reverse damage that has already happened. At CHOC, we offer the only pediatric blood and marrow transplant program in Orange County with experience in hematopoietic cell transplantation for MPS I. Learn more about the Blood and Marrow Transplantation (BMT) Program.

Enzyme replacement: Recombinant enzyme products are available for the treatment of specific types of MPS. Depending on the enzyme that is deficient or missing, the appropriate enzyme replacement may help in reducing some of the symptoms associated with whatever disease is being treated. Research has shown that liver and spleen enlargement, as well as exercise endurance, may improve with enzyme replacement therapy. CHOC Children’s can provide provide treatment for all forms of MPS for which enzyme replacement is approved by the U.S. Food and Drug Administration.

Surgery: Various types of surgery have been performed depending on the symptom being treated. For patients with sleep apnea and obstructive airway disease, the removal of tonsils and adenoids may be beneficial in improving breathing. Surgery has also been used to relieve compression on nerves and the spinal cord, repair hernias, fix heart abnormalities, and to place shunts to allow for drainage of cerebrospinal fluid. Our MPS Multidisciplinary Center offers pediatric surgeons in all areas to address any of these needs. Learn more about having surgery at CHOC.

Genetic testing and counseling: Individuals with a family history of MPS or who have MPS may meet with genetic counselors to discuss the risks of having additional affected children, and counseling for reproductive options.