Mucopolysaccharidoses (MPS) are a group of genetic disorders that affect primarily the body’s connective tissue. Connective tissue provides a support structure for the tissues and organs in our body, including bone, tendons, skin, the heart, eye and in many cases, the brain. The MPS disorders are divided into categories that are based on specific clinical and biochemical features. The prevalence of all forms is estimated to be one in 25,000 births.
What Is MPS?
The MPS disorders are also described as lysosomal storage disorders. Lysosomes are specialized compartments within our cells containing enzymes that break down large molecules that are no longer needed. In people with MPS disorders, certain enzymes are absent or deficient (do not work properly). These enzymes would normally break down complex carbohydrates called glycosaminoglycans (GAGs), formerly called mucopolysaccharides. This leads to a build-up of GAGs that causes progressive damage to cells, tissues and organs throughout the body.
The tiny blue circles represent lysosomes inside a cell. They have enzymes that break down GAGs which are then taken away to be recycled or discarded as waste. This continuous process helps to keep our cells and bodies healthy.
When someone has an MPS, the lysosomes lack the enzymes needed to break down GAGs, so they build up inside cells. The large black and gray shapes represent lysosomes that are enlarged and swollen with GAGs. This damages cells and causes health problems.
What Causes MPS?
Genes carry the instructions our bodies use to make products we need to grow and stay healthy, including the enzymes responsible for breaking down GAGs. Changes in specific genes result in a deficiency or absence of these important enzymes, and this causes the MPS disorders.
What Are Signs & Symptoms of MPS Disorders?
Clinical features of these conditions vary depending on the specific MPS diagnosis. However, people with MPS disorders share some similar symptoms: multiple organs are affected, a coarsening of facial features and abnormalities of the skeleton that lead to joint problems. Other signs and symptoms may be short height, abnormalities of the heart, breathing problems, and enlargement of the liver and spleen. The severity of the different MPS disorders varies widely, even among family members with the same type of MPS disorder.
Mild forms of the MPS disorders may not draw attention until childhood or adolescence. Initial symptoms may include frequent colds and infections, a persistent runny nose, not growing at the expected rate for the child’s age and mild developmental delays.
How Are MPS Disorders Diagnosed?
In most cases a child is suspected of having an MPS disorder after developing characteristic physical findings. The physical findings vary depending on the type of MPS disorder, and the diagnosis is confirmed by laboratory testing.
In Illinois, MPS I and MPS II are on the newborn screen. All babies born in the state are tested in their first days of life for many disorders and conditions. The tests that are included on the newborn screen are for disorders that would benefit from early treatment, even before the infant showed any signs or symptoms.
How is MPS Treated?
For all types of MPS treatment addresses a patient’s specific symptoms. At Lurie Children’s, the Division of Genetics regularly works with Orthopaedics, ENT, Sleep Medicine, Cardiology, Radiology and other specialties on treatment plans for our MPS patients. Supportive staff members are available to assist patients and families with their medical, emotional and social needs.
For some patients with MPS I, II, IVA, VI and VII enzyme replacement therapy (ERT) is an available treatment. ERT involves an infusion of a commercial form of the enzyme that is absent or deficient. It is given intravenously (through the vein) on a regular basis, most often twice per month. The infused enzyme helps to breakdown the GAGs that are building up in the body’s cells. The FDA-approved ERTs currently prescribed in the US include: laronidase (Aldurazyme®) for MPS I, idursulfase (Elaprase®) for MPS II, elosufase alfa (Vimizim®) for MPS IVA, galsidase (Naglazyme®) for MPS VI, and vestronidase alfa-vjbk (MepseviiTM) for MPS VII.
In addition, at Lurie Children's patients with the severe form of MPS I (Hurler syndrome) may undergo stem cell transplantation. The stem cell transplant program is one of the largest pediatric outpatient programs in the nation. Reggie Duerst, MD, leads a stem cell unit which has performed over 700 transplants in pediatric patients. The stem cell unit continues to explore new innovations in transplantation. The state-of-the-art facility allows the stem cell unit to provide all-inclusive care.
What Are the Long-Term Effects of MPS Disorders?
In most cases, MPS disorders are chronic and progressive. Depending on the type of MPS and severity, in general, a patient’s health declines over time.
The MPS and ML Treatment Program at Lurie Children’s