Hunter Syndrome Symptoms and Treatment

Mucopolysaccharidosis type II (MPS II), also known as Hunter syndrome, is an inherited disorder which causes a deficiency of the enzyme iduronate-2-sulfatase (I2S). 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 how Hunter syndrome is inherited, the condition is more common in men—although women, in rare cases, can inherit the condition too. Hunter syndrome can occur in any ethnic group. A slightly higher incidence has been noted among Jewish people living in Israel. The condition occurs in 1 in 100,000 to 1 in 150,000 males.

There are two types of Hunter syndrome—early-onset and late.

Early-Onset MPS II

The severe form of Hunter syndrome, early-onset, is usually diagnosed in children aged 18 to 36 months. Life expectancy for this form can vary, with some children living until their second and third decades of life. Symptoms of the early-onset disease 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 similar to those of Hurler syndrome. However, Hurler syndrome symptoms develop faster and are worse than those of early-onset Hunter syndrome.

Late MPS II

This type of Hunter syndrome is much milder than early-onset and may not be diagnosed until adulthood. Individuals with the late form of the disease have a much longer life expectancy and may live into their 70s. Their physical features are similar to those with severe MPS II; however, people with the late version of MPS II usually have normal intelligence and are lacking the severe skeletal problems of the more severe type.

Diagnosis

For severe 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. Mild 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. An enzyme study or genetic test for changes in the iduronate sulfatase gene can also diagnose the condition. Mucopolysaccharides may also be present in the urine. X-rays can reveal bone changes characteristic of Hunter syndrome.

Treating MPS II

Currently, there is no cure for Hunter syndrome. Medical care is directed towards relieving the symptoms of MPS II. 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 are 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 advise family and relatives about the risks of passing on the syndrome.