What causes Fragile-X syndrome?

Fragile-X syndrome affects the developing brain, while the baby is still a fetus. In 1991, researchers found that people with Fragile-X have an altered version of a gene that makes a brain protein. This DNA variant causes the gene to be switched off, so it no longer makes any protein. Scientists don't yet know how this protein usually functions in the developing brain.

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Chromosomes from a boy with Fragile-X syndrome, showing the 'fragile' point of the X-chromosome (arrowed).

How is Fragile-X syndrome inherited?

An altered gene on the X-chromosome causes Fragile-X syndrome. A girl will normally have a working gene on her other X-chromosome, which partially makes up for the altered gene, so girls are usually less severely affected than boys. The genetic change in Fragile-X is very unusual; it tends to change between parent and child, so predicting the exact risk of having an affected child is complicated.

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Inheritance of Fragile-X syndrome.


Principal Funder:

Wellcome trust

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