Role of the IDS enzyme
This genetic error leads to a defect in an enzyme called iduronate-2-sulfatase, abbreviated as IDS. This enzyme also plays an important role in the cell’s waste disposal and recycling system. Under normal circumstances, the IDS enzyme is involved in breaking down mucopolysaccharides (large sugar molecules) into smaller sugars, which are then returned to the cell. When this enzyme is missing or does not function properly, carbohydrates accumulate. This is why Hunter syndrome is classified as a “storage disorder.” The buildup of carbohydrates affects all cells and tissues in the body.
Who can be affected?
Boys and men can develop Hunter syndrome because the IDS gene is located on the X chromosome. Girls and women can be carriers, meaning they have one copy of the altered gene, but they are usually not affected themselves and typically do not show symptoms.
Types of Hunter syndrome
There are two forms of Hunter syndrome: a severe form and a milder form.
Severe form
In the severe form, symptoms begin when the patient is still an infant or toddler, often before the age of two. About 60% of patients with Hunter syndrome develop this severe form. Symptoms are more pronounced and the disease progresses more rapidly. In children with the severe form, the brain is affected. They may lose skills they had previously acquired, such as walking or speaking. Problems with thinking, behavior, and sleep are also common.
These children often have distinctive facial features, including a broad nose, thick lips, and a large tongue. Other symptoms include breathing and heart problems, hearing loss, and an enlarged liver. With current treatment (enzyme replacement therapy), children with the severe form typically live to be 10 to 20 years old.
Milder form
In the milder form, children initially develop normally, with the first symptoms appearing only after the age of four. In this form, the brain is not affected. Symptoms progress more slowly and are generally less severe, depending on the patient and the specific symptom.
Limitations of current treatment
Because current treatment with enzyme replacement therapy does not reach the brain, childhood dementia can occur. This condition is progressive and worsens as the child gets older.
New possibilities: gene therapy
Early research results from the gene therapy being developed by LentiCure suggest that this approach may reach the brain. Further research is needed to confirm these findings.
More information
For more information about the disease and the enzyme replacement therapy currently available, see:
