MPS II; Hunter syndrome; Lysosomal storage disease - mucopolysaccharidosis type II; Iduronate 2-sulfatase deficiency; I2S deficiency
Mucopolysaccharidosis type II (MPS II) is a rare disease in which the body is missing or does not have enough of an enzyme needed to break down long chains of sugar molecules. These chains of molecules are called glycosaminoglycans (formerly called mucopolysaccharides). As a result, the molecules build up in different parts of the body and cause various health problems.
The condition belongs to a group of diseases called mucopolysaccharidoses (MPSs). MPS II is also known as Hunter syndrome.
There are several other types of MPSs, including:
MPS II is an inherited disorder. This means it is 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
- 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:
Exams and Tests
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 --
- National Organization for Rare Disorders --
- NIH Genetic and Rare Diseases Information Center --
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
When to Contact a Medical Professional
Call 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.
Pyeritz RE. Inherited diseases of connective tissue. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 244.
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.
Last reviewed on: 5/2/2021
Reviewed 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 Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.