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IDS gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

IDS gene

The IDS gene provides instructions for an enzyme essential for breaking down complex sugar molecules, and its deficiency leads to Hunter syndrome.

Normal Function

The IDS gene provides instructions for producing an enzyme called iduronate 2-sulfatase (I2S). This enzyme is essential for the breakdown of large sugar molecules called glycosaminoglycans (GAGs). Specifically, I2S removes a sulfate chemical group from heparan sulfate and dermatan sulfate. I2S is located in lysosomes, which are compartments within cells that digest and recycle different types of molecules.

Health Conditions Related to Genetic Changes

Mucopolysaccharidosis type II

Hundreds of variants in the IDS gene have been found to cause mucopolysaccharidosis type II (MPS II), also known as Hunter syndrome. These variants reduce or completely eliminate the function of the I2S enzyme. There are two types of MPS II:

  • Neuropathic form: More severe; often caused by variants that remove large pieces of the gene or rearrange genetic material.
  • Non-neuropathic form: Less severe.

Lack of I2S enzyme activity leads to the accumulation of heparan sulfate and dermatan sulfate within lysosomes. This buildup increases the size of the lysosomes, causing many tissues and organs to become enlarged. Researchers believe the accumulated GAGs may interfere with other protein functions, disrupt intracellular movement, and trigger the release of cytokines that stimulate inflammation, contributing to the progression of the disorder.

Frequently Asked Questions

The IDS gene is located on the X chromosome, meaning Hunter syndrome (MPS II) is an X-linked recessive condition. Males have only one X chromosome, so a single altered copy of the IDS gene causes the disease. Females have two X chromosomes; if they inherit one mutated IDS copy, the normal gene on the other X chromosome typically provides sufficient enzyme activity, making females unaffected carriers who rarely experience significant symptoms.
Early warning signs usually appear between ages 18 months and 4 years. They include recurrent upper respiratory tract infections, persistent ear infections with progressive conductive or sensorineural hearing loss, umbilical or inguinal hernias that often recur after surgical repair, progressive joint stiffness without inflammatory swelling, and a gradual coarsening of facial features.
Diagnosis typically begins with a quantitative urine test to check for elevated levels of glycosaminoglycans (GAGs), specifically heparan sulfate and dermatan sulfate. If levels are elevated, definitive confirmation requires an enzymatic assay measuring iduronate 2-sulfatase activity in white blood cells or cultured skin fibroblasts, alongside comprehensive IDS molecular genetic sequencing to detect specific pathogenic variants.
Enzyme replacement therapy (ERT) with recombinant iduronate 2-sulfatase (such as idursulfase) helps reduce liver and spleen enlargement, improves joint mobility, and enhances respiratory function. However, standard intravenous ERT cannot cross the blood-brain barrier. Consequently, it does not prevent or reverse cognitive decline and progressive neurological symptoms in individuals with the severe, neuropathic form of Hunter syndrome.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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