What is Mucopolysaccharidosis Type II?
Mucopolysaccharidosis type II (MPS II), also known as Hunter syndrome, is an inherited lysosomal storage disorder. MPS II is caused by harmful changes (mutations) in the IDS gene. The symptoms associated with MPS II are caused by a buildup of harmful substances in different organs and tissues of the body. MPS II is inherited in an X-linked manner, which means that the IDS gene is located on the X chromosome. Males have one copy of the X-chromosome and the IDS gene, while females have two copies. Because of this, MPS II primarily affects males. It is rare for females to have symptoms of MPS II, and their symptoms are typically much more mild.
For males with MPS II, the onset of symptoms and disease severity can be variable. Characteristic features include coarse facial features (broad noses, large tongues, and thick lips); enlarged heads; recurrent ear infections; enlarged livers and spleens; hernias; thickened, pebbled skin; and short stature. Generally, individuals with a severe form of the condition present with symptoms between 18 months and four years of age. Approximately two-thirds of affected males will have central nervous system (CNS) involvement, leading to severe neurological decline and intellectual disability. Other major features include skeletal abnormalities (short stature, joint deformities, and limited joint mobility); hearing loss; heart abnormalities; and airway obstruction, which leads to pauses in breathing and progressive respiratory disease.
For individuals with a milder form of MPS II, the onset of non-CNS-related symptoms can occur in infancy or early childhood, although onset can also occur later than in those with a severe form of MPS II. The severity of the disease and its progression can vary significantly, but heart disease and hearing loss are still common. Individuals with a milder form of MPS II often have normal neurologic and motor development.
How common is Mucopolysaccharidosis Type II?
The frequency of MPS II in the general population varies by region but is approximately 1 in 100,000 to 1 in 170,000 males. Incidence may be higher in individuals of eastern Asian descent.
How is Mucopolysaccharidosis Type II treated?
There is no cure for MPS II. Treatment focuses on management of symptoms, for example, physical and occupational therapy for developmental delays or surgical valve replacement for heart abnormalities. Enzyme-replacement therapy (using idursulfase) is also available for treatment of non-CNS-related complications, though the success of treatment depends on the severity of disease. Treatment via bone-marrow transplant and stem-cell transplant have been attempted, though more data is needed to determine their long-term effectiveness.
What is the prognosis for an individual with Mucopolysaccharidosis Type II?
For those with severe disease, death typically occurs in the first or second decade of life. Individuals with a milder form of MPS II can have complications that lead to death in their twenties or thirties, though survival into the fifties and sixties has been reported.