Hunter syndrome overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:
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Overview
Hunter syndrome is a lysosomal storage disease caused by a deficient (or absent) enzyme, iduronate-2-sulfatase (I2S).
Historical Perspective
The syndrome is named after physician Charles A. Hunter (1873-1955), who first described it in 1917. Born in Scotland, Hunter emigrated to Canada and had a medical practice in Winnipeg, Manitoba.
Classification
Pathophysiology
Hunter syndrome is a serious genetic disorder that primarily affects males. It interferes with the body's ability to break down and recycle specific mucopolysaccharides, also known as glycosaminoglycans or GAG. Hunter syndrome is one of several related lysosomal storage diseases.
Causes
Differentiating Hunter syndrome from Other Diseases
Epidemiology and Demographics
There are estimated to be approximately 2,000 people afflicted with Hunter Syndrome worldwide, 500 of which live in the United States.
Risk Factors
Screening
The most commonly used laboratory screening test for an MPS disorder is a urine test for GAG. It is important to note that the urine test for GAG can occasionally be normal and yet the child still may have an MPS disorder.
Natural History, Complications and Prognosis
Not all people with Hunter syndrome are affected by the disease in exactly the same way, and the rate of symptom progression varies widely. However, Hunter syndrome is always severe, progressive, and life-limiting.
Diagnosis
History and Symptoms
The symptoms of Hunter syndrome (MPS II) are generally not apparent at birth, but usually start to become noticeable after the first year of life. Often, the first symptoms of Hunter syndrome may include inguinal hernias, ear infections, runny noses, and colds. Since these symptoms are quite common among all infants, they are not likely to lead a doctor to make a diagnosis of Hunter syndrome right away. As the buildup of GAG continues throughout the cells of the body, signs of Hunter syndrome become more visible.
Physical Examination
Physical manifestations for some people with Hunter syndrome include distinct facial features, a large head, and an enlarged abdomen. People with Hunter syndrome may also experience hearing loss, thickening of the heart valves leading to a decline in cardiac function, obstructive airway disease, sleep apnea, and enlargement of the liver and spleen. Range of motion and mobility may also be affected. In some cases of Hunter syndrome, central nervous system involvement leads to developmental delays and nervous system problems.
Laboratory Findings
A definitive diagnosis of Hunter syndrome is made by measuring I2S activity in serum, white blood cells, or fibroblasts from skin biopsy. In some people with Hunter syndrome, analysis of the I2S gene can determine clinical severity. Prenatal diagnosis is routinely available by measuring I2S enzymatic activity in amniotic fluid or in chorionic villus tissue.
Imaging Findings
Other Diagnostic Studies
Treatment
Medical Therapy
On July 24, 2006, a synthetic version of I2S, called Elaprase (Idursulfase), was approved by the United States Food and Drug Administration as an enzyme replacement treatment for Hunter syndrome. Elaprase is a purified form of the lysosomal enzyme iduronate-2-sulfatase and is produced by recombinant DNA technology in a human cell line. Elaprase may be one of the most expensive drugs ever produced, with an estimated cost of USD300,000 per patient, per year. [1]