Hunter syndrome

Hunter's syndrome is a mucopolysaccharide disease caused by an enzyme deficiency of iduronate-2-sulfatase (I2S). This is also called as mucopolysaccharoidosis Type II. It was first described by Scottish physician Charles A. Hunter (1873-1955) in 1917. more...

Definition

Hunter syndrome is a hereditary disease in which the breakdown of a mucopolysaccharide (a chemical that is widely distributed in the body outside of cells) is defective. This chemical builds up and causes a characteristic facial appearance, abnormal function of multiple organs, and in severe cases, early death.

Causes, incidence, and risk factors

Hunter syndrome is inherited as an X-linked recessive disease. This means that women carry the disease and can pass it on to their sons, but are not themselves affected.

Because girls have two X chromosomes, their normal X can provide a functioning gene even if their other X is defective. But because boys have an X and a Y, there is no normal X gene to fix the problem if the X is defective.

The metabolic abnormality that causes Hunter syndrome is a lack of the enzyme iduronate-2-sulfatase. In its absence, mucopolysaccharides collect in various body tissues, causing damage.

Affected children may develop an early-onset type (severe form) shortly after age 2 that causes a large skull, coarse facial features, profound mental retardation, spasticity, aggressive behavior, joint stiffness and death before age 20. A late-onset type (mild form) causes later and less severe symptoms.

Symptoms

Juvenile form (early-onset, severe form):

• mental deterioration
• severe to profound mental retardation
• aggressive behavior
• hyperactivity
• short stature

Late (mild form):

• mild to no mental retardation

Both forms:

• coarse facial features
• large head (macrocephaly)
• stiffening of joints
• increased hair (hypertrichosis)
• deafness (progressive)
• enlargement of internal organs such as liver and spleen
• cardiovascular problems, especially valvular dysfunction
• abnormal retina (back of the eye)
• carpal tunnel syndrome

Signs and tests

Signs of the disorder that the doctor might look for include:

• hepatomegaly (enlargement of liver)
• splenomegaly (enlargement of spleen)
• inguinal hernia
• spasticity
• heart murmur and heart valve dysfunction
• joint contractures
• excretion of heparan sulfate and dermatan sulfate in urine
• decreased iduronate sulfatase enzyme activity in serum or cells

Tests that may indicate this disorder is present include:

• urine for heparan sulfate and dermatan sulfate
• enzyme study, decreased iduronosulfate sulfatase (may be studied in serum, white blood cells and fibroblasts)
• genetic testing may show mutation in the iduronate sulfatase gene

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