Mucopolysaccharidosis Type 1 (MPS I): Causes and Symptoms

What is mucopolysaccharidosis, Type 1?

Mucopolysaccharidosis, type 1 (MPS I) is a genetic condition in which the body creates too little alpha-iduronidase enzyme (an enzyme that helps the body break down certain types of sugar). There is a spectrum of disease ranging from severe- MPS I (when symptoms start in infancy) to attenuated MPS I (when symptoms start between ages 3-10 years old).

What are the symptoms of MPS I?

Without treatment, people with MPS I may have the following symptoms:

Severe MPS i

• Facial features that are pronounced (larger or more noticeable)
• Gibbus deformity (a pronounced curve in the spine)
• Obstructive sleep apnea (a condition in which the muscles in the back of the throat relax too much and affect a person’s breathing while they sleep)
• Corneal clouding (cloudy appearance of the cornea, or the clear, protective outer layer of the eye)
• Ear infections and hearing loss
• Intellectual disability
• Short stature (short height)
• Skeletal problems (conditions that affect the bones)

Attenuated MPS i

• Cardiorespiratory disease (disease that affects the heart and lungs)
• Progressive joint problems (conditions that affect the joints and get worse over time)
• Hearing loss
• Corneal clouding

What causes MPS I?

MPS I is caused by changes in the IDUA gene. Genes are the instructions that tell our bodies how to develop and function. The job of the IDUA gene is to create the alpha iduronidase enzyme. People with certain mutations (changes or misspellings) in the IDUA gene create too little or no alpha-iduronidase enzyme.

MPS I is inherited (passed down from parent to child) in an autosomal recessive pattern (when a child inherits a mutated gene from each parent who carries the gene for the condition but does not have the condition itself). Our genes come in pairs. We get one copy from our biological mother and the other from our biological father. In MPS I, both copies of the IDUA gene have a mutation that causes it to create less or no alpha iduronidase enzyme.

Rev. 6/2022. Mass General for Children and Massachusetts General Hospital do not endorse any of the brands listed on this handout. This handout is intended to provide health information so you can be better informed. It is not a substitute for medical advice and should not be used to treat any medical conditions.