What is Hunter Syndrome?
Hunter syndrome is a type of mucopolysaccharidosis.
Hunter syndrome is also called mucopolysaccharidosis II (MPS II). It is a lysosomal storage disease caused by a deficient (or absent) enzyme, iduronate-2-sulfatase. This deficiency results in accumulation of heparan sulfate and dermatan sulfate.
It is a sex linked condition, therefore the male inherits the disease from his mother, either through a mutation in her X-chromosome or through an abnormal X-chromosome inherited by her from an earlier generation.
Lack of enzyme iduronate 2 sulphatase interferes with the body’s ability to break down and recycle glycosaminoglycans or GAG mainly heparan sulphate and dermatan sulphate, which gets accumulated in the body as a result.
Interferes with normal working of cells and cause symptoms which differ from person to person.
Clinical Features of Hunter Syndrome
Symptoms noticeable usually after the first year of life.
- abdominal hernias, ear infections, runny noses, and colds.
- Physical Features
- prominent forehead, a nose with a flattened bridge, and an enlarged tongue.
- Large head
- Enlarged abdomen.
- Obstructive lung disease
- Limited lung capacity
- Enlargement of liver and spleen
- Joint stiffness
- If carpal tunnel syndrome
- short stature
- Ivory-colored skin lesions
- Delayed development with subsequent mental retardation and progressive loss of function. The rate and degree of progression may be different for each person with Hunter syndrome.
Comparison with Hurler Syndrome
The skeletal features of dwarfism and joint deformities are similar to those of mucopolysaccharidosis I-H or Hurler’s Syndrome but less marked. Spine deformity is less marked and acute kyphosis does not usually develop.
Hepatosplenomegaly is present but corneal clouding and opacities do not develop and mental retardation is minimal and occurs late.
Heparan sulphate is the main glycosaminoglycan excreted in the urine, with lesser amounts of dermatan sulphate. The casual enzymatic defect is a sulpho-iduronate sulphatase.
Radiological Appearance of Hunter Syndrome
The radiological appearances, though mild, are typical of a mucopolysaccharidosis. The ribs are short, wide and paddle-shaped and the vertebral bodies show anterior prominence, particularly at the lower border. The pelvis shows a slight hour-glass appearance but the hips are normal.
The hands show the most clear changes, with thickened metacarpals with square bases, and small, mildly deformed phalanges which are cone-shaped.
The bony changes are generally like those in Hurler’s syndrome but usually less severe. Many patients do not have a kyphos, or a beaked, notch or hooked vertebra and the pelvic changes are less marked, but there is a spectrum of abnormality that may approach the degree of bony change in Hurler’s syndrome. In older patients, irregularity of the bones of the hip predisposes to early osteoarthritis.
- Measuring iduronate 2 sulphatase activity
- white blood cells
- fibroblasts from skin biopsy.
- Analysis of the iduronate 2 sulphatase gene can determine clinical severity.
- Prenatal diagnosis is available by measuring iduronate 2 sulphatase enzymatic activity in amniotic fluid or in chorionic villus tissue.
Idursulfase is a purified form of the lysosomal enzyme iduronate-2-sulfatase produced by recombinant DNA technology in a human cell line. This provides the replacement of enzyme. But the cost is a major deterrent.
Corrective and Palliative Surgeries
In severe cases with extensive visceral manifestations, surgery has little to offer but in patients with the probability of survival into adolescence, deformities that interfere with daily management may deserve correction..
A mild, and probably distinct form of Hunter’s syndrome has been recognized in which there are much less severe bone and joint deformities, no significant mental retardation and longevity compatible with life up to 50 years.
Genu valgum may require correction by epiphysial stapling or supracondylar osteotomy. If an equinus deformity is present elongation of tendocalcaneus helps.
Limitation of movements in the joints of the upper limb is not usually sufficiently disabling to need treatment.