Mucopolysaccharidosis type II

Alternative names

Hunter syndrome, Iduronate sulfatase deficiency

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 afffected.

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 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 mental retardation
  
• aggressive behavior
  
• hyperactive
  

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
  

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