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Do identical twins have the same HD status?

February 2, 2015

Huntington's Disease Youth Organization

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Do identical twins have the same HD status?

Q. If the genetic testing for Huntington’s Disease of an identical sibling is positive does it mean that the other has it as well automatically because they have the same genes? Or does the other also have a 50:50 chance?

Susanne, Young Adult, Germany

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A. Dear Susanne,

Thank you for this question.

If the sibling is truly an identical twin, then if one has a positive HD genetic test, then the other will also be positive. So the chance would be 100:0 not 50:50. This is because both siblings have the same genes and HD is a genetic condition.

In this case, there would also need to be verification that the twins were truly identical. Sometimes, it is not automatically obvious whether twins are identical or not.

This means that, if one identical twin is considering taking the test, the position of other twin needs to be considered.

Best wishes

Hugh