Hunter syndrome Health Article

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.

Alternative Names

Mucopolysaccharidosis type II, Iduronate sulfatase deficiency

Causes, incidence, and risk factors

Hunter syndrome is inherited as an X-linked recessive disease. This means that boys will be the ones most often affected, because the defective gene is on the X chromosome. Boys have only 1 copy of the X chromosome. Girls have 2 copies.

Because girls have two X chromosomes, their normal copy on one X can provide a functioning gene, even if their other X has the abnormal gene. Women can carry the defective gene and pass it on, without being affected themselves, unless both their copies are abnormal. 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 sulfatase. Without this enzyme, 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 mental retardation
• Aggressive behavior
• Hyperactivity

Late (mild) form:

• Mild to no mental deficiency

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
• Abnormal retina (back of the eye)
• Carpal tunnel syndrome