Understanding Your Child's MPS I Diagnosis

Receiving a diagnosis of Mucopolysaccharidosis type 1 (MPS I) is a life-altering moment that often brings a mix of shock and confusion. It is important to remember that while this condition is rare and complex, there is a dedicated community of specialists and families—such as the National MPS Society—ready to help you navigate the road ahead.

What is MPS I?

MPS I is a rare genetic disorder occurring in approximately 1 out of every 100,000 to 150,000 live births ^[1][2][3]. It is a lysosomal storage disorder, which means it affects the “recycling centers” (lysosomes) of the body’s cells ^[4].

In a healthy body, an enzyme called alpha-L-iduronidase (IDUA) breaks down complex sugar molecules known as glycosaminoglycans (GAGs) ^[4][5]. In children with MPS I, this enzyme is either missing or not functioning correctly ^[4]. As a result, GAGs—specifically dermatan sulfate and heparan sulfate—build up in tissues throughout the body ^[5]. This accumulation acts like a “clog” in the cells, eventually leading to progressive damage in the heart, bones, joints, and sometimes the brain ^[6][5].

Learn more about the underlying genetics and how this condition is diagnosed in The Biology of MPS I and Understanding Your Diagnosis.

The MPS I Spectrum

MPS I is a spectrum disorder, meaning it affects every person differently ^[7]. Doctors generally group it into two main categories based on the severity of symptoms ^[6][4].

Severe MPS I (Hurler Syndrome)

The severe form, traditionally known as Hurler syndrome, usually appears in infancy, with symptoms often starting within the first 6 months of life ^[6][8].

• Early Signs: Early indicators can include frequent ear infections, respiratory issues, and umbilical or inguinal hernias ^[8][9].
• Physical Features: As the condition progresses, children may develop kyphosis (a curved lower spine), corneal clouding (hazy vision), and an enlarged liver or spleen (hepatosplenomegaly) ^[8][9][5].
• Neurological Impact: This form involves the central nervous system, leading to a rapid decline in cognitive development ^[6][10].

Attenuated MPS I (Hurler-Scheie and Scheie Syndromes)

The attenuated forms (meaning milder or slower-progressing), which include Hurler-Scheie and Scheie syndromes, progress more slowly and may not be diagnosed until late childhood or even adulthood ^[10][11].

• Somatic Issues: While these children usually do not experience the rapid brain decline seen in the severe form, they face significant physical or “somatic” challenges ^[10][12].
• Hallmark Symptoms: Common issues include severe joint stiffness, carpal tunnel syndrome, and heart valve disease (such as aortic or mitral stenosis) ^[12][11][7]. Individuals with the mildest form (Scheie) often have a normal life expectancy and normal intelligence but may live with significant physical disabilities ^[9][11].

Read more about the differences in presentation in Symptoms, Warning Signs, and Avoiding Misdiagnosis.

Next Steps and Treatment

Your care team will use genetic testing and enzyme assays to determine where your child falls on the spectrum ^[5]. This classification is the most important step in choosing a treatment path—whether that is a stem cell transplant for severe cases or enzyme replacement therapy for attenuated forms ^[6][13]. Early intervention is the most effective way to slow or prevent the most serious complications of the disease ^[6][10].

Explore the different treatment pathways in Standard of Care Treatment Options: HSCT vs ERT and how to manage the condition over time in Building Your Care Team and Managing Long-Term Health.