Who gets it?
Hunter syndrome is an X-linked disorder, meaning that it is transmitted on the female X chromosome from a mother to her children. Therefore, the syndrome is most often seen in males, although rare female cases have been reported. Hunter syndrome can occur in any ethnic group; a slightly higher incidence has been noted in the Jewish population living in Israel. It may occur as frequently as 1 individual per 65,000 births to as rarely as 1 individual in 132,000 births.
Type A
Hunter syndrome is divided into two types. Type A is the severe form, which usually is diagnosed in children aged 18-36 months. It is considered the classic form. Children with type A may survive into the second and third decades of life. Symptoms in type A may include:
- coarse facial features and short stature
- enlarge liver and spleen
- progressive and profound mental retardation
- ivory-colored skin lesions on the upper back and sides of the upper arms and thighs
- skeletal changes, joint stiffness, short neck, broad chest, and too-large head
- progressive deafness
- atypical retinitis pigmentosa and visual impairment
Type B
Type B Hunter syndrome is much milder than type A and may not be diagnosed until adulthood. Individuals with type B may live into their 70s. Their physical features are similar to those in type A. Individuals with type B, however, usually have normal intelligence and do not have the severe skeletal problems of type A.
Diagnosis
In type A Hunter syndrome, the child's appearance combined with other symptoms such as enlarged liver and spleen and the ivory-colored skin lesions (considered a marker for the syndrome) can suggest the child has mucopolysaccharidosis. Type B Hunter syndrome is much harder to identify, and might only be recognized when looking at the maternal relatives of a child with Hunter syndrome.
In either type, the diagnosis can be confirmed by a blood test for deficiency of I2S. Also, mucopolysaccharides may be present in the urine. X-rays can reveal bone changes characteristic of Hunter syndrome.
Treatment
No cure yet exists for Hunter syndrome, so medical care is directed towards relieving its symptoms. The respiratory tract may become obstructed from cell damage, so good respiratory care and monitoring is important. Many specialists are involved in the care of an individual with Hunter syndrome, including a geneticist to counsel the family and relatives about transmission of the syndrome.
Enzyme replacement
Researchers have been testing to see whether a synthetic form of I2S can stop Hunter syndrome from getting worse. Shire plc (which purchased Transkaryotic Therapies) has conducted clinical trials on its version, called Elaprase, studying its effects in 96 individuals with Hunter syndrome over 52 weeks. Shire has applied to both the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMEA) for marketing approval of Elaprase.
Last updated 12/21/05
Information for this article was taken from:
- Fenton, C. I. (2002). Mucopolysaccharidosis Type II. eMedicine, accessed at http://www.emedicine.com/ped/topic1029.htm.
- ClinicalTrials.gov. Iduronate-2-sulfatase Enzyme Replacement Therapy in Mucopolysaccharidosis II (MPS II). Accessed at http://www.clinicaltrials.gov.
