Mucopolysaccharidosis (Type I)

What is Mucopolysaccharidosis, Type I?
Mucopolysaccharidosis Type I (MPS I) is a rare genetic disorder caused by the absence of, or reduced activity of, an enzyme called alpha-L-iduronidase. This causes the buildup of large sugar molecules called glycosaminoglycans (GAGs) within the body's cells; this accumulation leads to enlarged organs and tissues. This disorder was once separated into three syndromes, Hurler (MPS I-H), Hurler-Scheie (MPS I-H/S), and Scheie syndrome (MPS I-S), but due to significant overlap of signs and symptoms the   classification changed to either severe or attenuated types.

What are the symptoms of Mucopolysaccharidosis?
The severe form of MPS I is a progressive disorder with multiple organ and tissue involvement that usually start within the first year of life. Symptoms may include nonspecific symptoms at birth such as hernia, leading to progressive mental retardation and developmental delays, skeletal deformities including short stature and stiff joints, speech and hearing impairment, corneal clouding, enlarged liver and spleen, coarse facial features, pain and a shortened life span due to heart and lung disease.

The attenuated form of MPS I is a milder, more variable form that can begin anywhere between ages three and 10 years. The rate of disease progression can range from normal life span complicated with significant disability from progressive physical manifestations to more life-threatening complications which can lead to death in the second to third decades due to heart and lung disease. Learning disabilities can be present in some and normal in others.

Is there treatment for Mucopolysaccharidosis?
Yes. There is FDA-approved treatment for confirmed MPS I to treat the non-neurological manifestations of the disease. Treatment involves a weekly intravenous (IV) infusion of alpha-L-iduronidase (Aldurazyme®) for life. Enzyme replacement therapy has shown to help reduce non-neurological symptoms and pain.

Bone marrow or hematopoietic stem cell transplantation replaces cells that produce the missing enzyme through either bone marrow or umbilical cord blood.  This high-risk treatment may be an option for more severe patients, however the risks and benefits should be discussed with the patients’ physician.

What is the prognosis?
There is no cure for MPS I, but the symptoms can be managed effectively if identified early. Due to the nature of this disease, the severity will vary across patients. Those diagnosed with the more severe MPS I often die by age 10 from respiratory and heart complications. While those diagnosed with the attenuated form can live into adulthood.

How is it inherited?
It is an autosomal recessive disease. This means that the mother and father must both pass one abnormal copy of the gene to the child in order for the child to develop the disease.

Source: Genetics Home Reference; GeneReviews; MedlinePlus; NINDS

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