Cardiovascular System

Clinical complications related to heart disease occur in all individuals with MPS I, particularly during the later stages of MPS I disease.[2] Evidence of cardiovascular involvement by echocardiography can be demonstrated much earlier than that derived from clinical observations.

Mildly affected people with the attenuated form of MPS I may develop problems with the aortic or mitral valves. Storage of GAGs within and around the valve leaflets results in their thickening and stiffening which can lead to progressive mitral and aortic regurgitation (Image 1).[1] In patients with severe MPS I, the valvular disease does not usually lead to hemodynamic effects until the later stages of disease. People with attenuated disease who have moderate to severe symptoms (Hurler-Scheie syndrome) can also develop valve disease and may need mitral or aortic valve replacement as early as their teens and twenties.[2]

Image 1 - Pathological specimen showing thickened and deformed valvular leaves
Courtesy of J.E. Wraith, MD

In severe patients, as GAG storage continues in the heart, cardiomyopathy may trigger sudden death related to arrhythmia, coronary artery disease and cardiovascular collapse. A small subset of severe MPS I patients exhibit early onset of fatal endocardiofibroelastosis, presenting in the first year of life. Mitral regurgitation is the more common valvular disease in severe MPS I.[1]

Valve replacement surgery may be considered early in association with a general assessment of a patient's clinical condition. Cardiac evaluation through serial monitoring of ventricular size, wall thickness and function at regular intervals at least every 2 years (according to Muenzer 2009) with echocardiography is useful in the treatment of patients. Bacterial endocarditis prophylaxis may be advised for MPS I patients with cardiac abnormalities.[2]

Next: Ocular System

Did You Know?

Genetic counselors are health professionals who are trained to help families understand genetic disorders such as MPS I disease. A genetic counselor can help you determine if you are a carrier of a gene defect that causes MPS I and can provide valuable information and support for family planning. To learn more, click here.


  1. Wippermann CF, Beck M, Schranz D, Huth R, Michel-Behnke I, Jungst BK. Mitral and aortic regurgitation in 84 patients with mucopolysaccharidoses. Eur J Pediatr 1995;154(2):98-101.
  2. Neufeld EF, Muenzer J. The Mucopolysaccharidoses. In: Valle D, Beaudet AL, Vogelstein B, Kinzler KW, Antonarakis SE, Ballabio A, Gibson K, Mitchell G. eds. The Online Metabolic and Molecular Bases of Inherited Disease New York, NY: McGraw-Hill; 2014. Accessed February 2019.