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Hunter Syndrome

Inherited storage disease

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Updated June 13, 2014

Mucopolysaccharidosis type II (MPS II), called Hunter syndrome, is an inherited disorder in which an enzyme, iduronate-2-sulfatase (I2S), is deficient. I2S is involved in the breakdown of complex carbohydrates called mucopolysaccharides. Without enough I2S, partially broken-down mucopolysaccharides accumulate in the organs and tissues of the body and become toxic.

Hunter syndrome is an X-linked disorder, meaning that it is transmitted on the X chromosome from a mother to her children. Because of this the syndrome is most often seen in males, although rare female cases have been reported. Hunter syndrome can occur in any ethnic group; a slightly higher incidence has been noted in the Jewish population living in Israel. It occurs in 1 in 100,000 to 1 in 150,000 males.

Type A

Hunter syndrome is divided into two types. Type A is the severe form, which usually is diagnosed in children aged 18-36 months. It is considered the classic form. Children with type A may survive into the second and third decades of life. Symptoms in type A may include:
  • coarse facial features and short stature
  • enlarged liver and spleen
  • progressive and profound mental retardation
  • ivory-colored skin lesions on the upper back and sides of the upper arms and thighs
  • skeletal changes, joint stiffness, short neck, broad chest, and too-large head
  • progressive deafness
  • atypical retinitis pigmentosa and visual impairment
These symptoms are very similar to those of Hurler syndrome, but Hurler syndrome symptoms become worse much faster than Hunter syndrome type A.

Type B

Type B Hunter syndrome is much milder than type A and may not be diagnosed until adulthood. Individuals with type B may live into their 70s. Their physical features are similar to those in type A. Individuals with type B, however, usually have normal intelligence and do not have the severe skeletal problems of type A.

Diagnosis

In type A Hunter syndrome, the child's appearance combined with other symptoms such as enlarged liver and spleen and the ivory-colored skin lesions (considered a marker for the syndrome) can suggest the child has mucopolysaccharidosis. Type B Hunter syndrome is much harder to identify, and might only be recognized when looking at the maternal relatives of a child with Hunter syndrome.

In either type, the diagnosis can be confirmed by a blood test for deficiency of I2S. Also, mucopolysaccharides may be present in the urine. X-rays can reveal bone changes characteristic of Hunter syndrome.

Treatment

Medical care is directed towards relieving the symptoms of Hunter syndrome. Treatment with Elaprase (idursulfase) replaces I2S in the body and helps reduce symptoms and pain. The respiratory tract may become obstructed, so good respiratory care and monitoring is important. Physical therapy and daily exercise are important. Many specialists are involved in the care of an individual with Hunter syndrome. A genetic counselor can talk with the family and relatives about the risks of passing on the syndrome.

Source:

"MPS II (Hunter syndrome)." MPS & Related Diseases. National MPS Society. 25 Mar 2009

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