What is Hunter Syndrome?

Hunter syndrome, or mucopolysaccharidosis II (MPS II), is a serious genetic disorder that primarily affects males. It interferes with the body’s ability to break down and recycle specific mucopolysaccharides (mew-ko-pol-ee-sak-ah-rides), also known as glycosaminoglycans (gli-ko-sah-mee-no-gli-cans) or GAGs. Hunter syndrome is one of several related lysosomal storage diseases.

This video provides an overview of Hunter syndrome. In Hunter syndrome, GAGs build up in cells throughout the body due to the enzyme iduronate-2-sulfatase (I2S) being deficient or missing altogether.

In Hunter syndrome, GAGs build up in cells throughout the body due to a deficiency or absence of the enzyme iduronate-2-sulfatase (I2S). This buildup interferes with the way certain cells and organs in the body function and leads to a number of serious symptoms. As the buildup of GAGs continues throughout the cells of the body, signs of Hunter syndrome become more visible. Physical manifestations for some people with Hunter syndrome include distinct facial features, a large head, and an enlarged abdomen. People with Hunter syndrome may also experience hearing loss, thickening of the heart valves leading to a decline in cardiac function, obstructive airway disease, sleep apnea, and enlargement of the liver and spleen. Range of motion and mobility may also be affected. In some cases of Hunter syndrome, central nervous system involvement leads to developmental delays and nervous system problems. Not all people with Hunter syndrome are affected by the disease in exactly the same way, and the rate of symptom progression varies widely. However, Hunter syndrome is progressive and life-limiting.

Two of the most significant areas of variability concern the degree of mental impairment and expected life span. Some people who have Hunter syndrome are not mentally impaired and live into their 20s or 30s; there are occasional reports of people who have lived into their 50s or 60s, and many adults are actively employed. In contrast, others with Hunter syndrome develop severe mental impairment and have shorter life expectancies.