MPS II is a genetic disorder. This means it can be passed down through families. The affected gene is on the X chromosome. Boys are most often affected because they inherit the X chromosome from their mothers. Their mothers do not have symptoms of the disease, but they carry a nonworking copy of the gene.

MPS II is caused by a lack of the enzyme iduronate sulfatase. Without this enzyme, chains of sugar molecules build up in various body tissues, causing damage.

The early-onset, severe form of the disease begins shortly after age 2. A late-onset, mild form causes less severe symptoms to appear later in life.

In the early-onset, severe form, symptoms include:

• Aggressive behavior
• Hyperactivity
• Mental function gets worse over time
• Severe intellectual disability
• Jerky body movements

In the late (mild) form, there can be mild to no mental deficiency.

In both forms, symptoms include:

• Carpal tunnel syndrome
• Coarse features of the face
• Deafness (gets worse over time)
• Increased hair growth
• Joint stiffness
• Large head

A physical exam and tests may show:

• Abnormal retina (back of the eye)
• Decreased iduronate sulfatase enzyme in blood serum or cells
• Heart murmur and leaky heart valves
• Enlarged liver
• Enlarged spleen
• Hernia in the groin
• Joint contractures (from joint stiffness)

Tests may include:

• Enzyme study
• Genetic testing for a change in the iduronate sulfatase gene
• Urine test for heparan sulfate and dermatan sulfate

The medicine called idursulfase (Elaprase), which replaces the enzyme iduronate sulfatase may be recommended. It is given through a vein (IV, intravenously). Talk to your health care provider for more information.

Bone marrow transplant has been tried for the early-onset form, but the results can vary.

Each health problem caused by this disease should be treated separately.

More information and support for people with MPS II and their families can be found at:

• National MPS Society -- mpssociety.org/
• National Organization for Rare Disorders -- rarediseases.org/rare-diseases/mucopolysaccharidosis-type-ii-2/
• NIH Genetic and Rare Diseases Information Center -- rarediseases.info.nih.gov/diseases/6675/mucopolysaccharidosis-type-ii

People with the early-onset (severe) form usually live for 10 to 20 years. People with the late-onset (mild) form usually live 20 to 60 years.

These complications may occur:

• Airway obstruction
• Carpal tunnel syndrome
• Hearing loss that gets worse over time
• Loss of ability to complete daily living activities
• Joint stiffness that leads to contractures
• Mental function that gets worse over time

Contact your provider if:

• You or your child has a group of these symptoms
• You know you are a genetic carrier and are considering having children

Genetic counseling is recommended for couples who want to have children and who have a family history of MPS II. Prenatal testing is available. Carrier testing for female relatives of affected males is also available.

MPS II; Hunter syndrome; Lysosomal storage disease - mucopolysaccharidosis type II; Iduronate 2-sulfatase deficiency; I2S deficiency

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Spranger JW. Mucopolysaccharidoses. In: Kliegman RM, St. Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM, eds. Nelson Textbook of Pediatrics. 21st ed. Philadelphia, PA: Elsevier; 2020:chap 107.

Turnpenny PD, Ellard S, Cleaver R. Inborn errors of metabolism. In: Turnpenny PD, Ellard S, Cleaver R, eds. Emery's Elements of Medical Genetics and Genomics.16th ed. Philadelphia, PA: Elsevier; 2022:chap 18.

Updated by: Anna C. Edens Hurst, MD, MS, Associate Professor in Medical Genetics, The University of Alabama at Birmingham, Birmingham, AL. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.