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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.

Inheritance of Fragile-X syndrome.
Inheritance of Fragile-X syndrome.

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