What is MPS I

MPS I is a rare inherited genetic disorder that affects many parts of the body. It is caused by the lack of an enzyme (lysosomal α-L-iduronidase) needed to break down certain complex sugars. As a result, these substances build up in the body and cause progressive damage over time.

MPS I is a progressive disease, meaning symptoms worsen as a person gets older. The condition exists on a spectrum, from very severe to milder forms. Today, doctors generally classify MPS I into two main types based on severity:

• Severe MPS I
• Attenuated (milder) MPS I

This classification helps determine the most appropriate treatment and long-term care.

Severe MPS I

Babies with severe MPS I usually appear healthy at birth. Early symptoms often begin within the first year of life and may include frequent infections or hernias. Changes in facial features typically become noticeable after the first year.

As the disease progresses, children develop:

Without treatment, severe MPS I leads to serious complications, and life expectancy is often limited to early childhood.

Attenuated (Milder) MPS I

Attenuated MPS I usually begins later, between early childhood and adolescence. Symptoms develop more slowly and vary greatly between individuals.

Common features include:

Intellectual development may be normal in early life, although learning difficulties or mental health challenges can appear later. Some people with attenuated MPS I have a shortened lifespan, while others live into adulthood but may experience significant physical limitations.