A hereditary disease in which the degradation of a mucopolysaccharide (a chemical that is widely distributed in the body outside of cells) is defective. Inability to break down this mucopolysaccharide leads to its accumulation and storage in body tissues. This storage is associated with 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. Females with one normal X and one defective X chromosome are disease free. Males with a defective X chromosome develop Hunter syndrome. 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 2 years that causes a large skull, coarse facial features, profound mental retardation , spasticity , aggressive behavior, joint stiffness and death before 20 years of age. A late-onset type (mild form) causes later and less severe symptoms with sparing of intelligence.
Signs and tests
hepatomegaly (enlargement of liver) splenomegaly (enlargement of spleen) inguinal herniaspasticity heart murmur and leaky heart valves 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, WBCs, fibroblasts)
Treatment
There is no specific treatment for Hunter syndrome. Individual problems should be addressed separately. Bone marrow transplant has been attempted for the early-onset form with variable results. In the future, enzyme replacement therapy will likely be the treatment of choice.
Expectations (prognosis)
Life expectancy for the early-onset form (severe form) is 10-20 years. Life expectancy for the late-onset form (mild form) is 20-60 years.
Calling your health care provider
Call your health care provider if you or your child manifest a group of these symptoms, or if you know you are a genetic carrier and are considering having children.
Prevention
Genetic counseling is recommended for prospective parents with a family history of Hunter syndrome. Prenatal testing is available. Carrier testing for female relatives of affected males is available at a few specialized centers.