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My mother did not have the gene, can I?

December 31, 2015

Huntington's Disease Youth Organization

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My mother did not have the gene, can I?

Q. My grandmother died of H.D my mother was tested and did not have the gene. Can I or my daughter still have the defective gene?

Alison, Young Adult, UK

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A. Dear Alison,

Many thanks for your question. If your mother has had genetic testing that shows she does not have the genetic change that causes HD, you (and your daughter) will also not be at any increased risk of HD.

This is because HD follows what is called ‘autosomal dominant’ inheritance. As you may know, everyone (whether at risk of HD or not) has two copies of the HD gene, and we inherit one copy from each parent. Huntington’s disease is caused when an individual has a specific change (an expansion in the ‘CAG repeats’) in one copy of the HD gene.

If your mother has had a genetic test for HD that shows she does not have it, this means that both copies of her HD gene must have ‘CAG’ repeat sizes within the normal range. Therefore, regardless of which copy of the gene you inherited from her, it would not cause you to have HD. In turn, if you do not carry a CAG expansion, your daughter cannot inherit one from you.

I hope this helps answer your question, but please get back to us if you have any further queries.

Best wishes

Bill