Do non-identical twins have 50% each chance of getting HD?
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Q. My partner’s mother has HD as she inherited from her mother. My partner has a twin brother (dizygotic). Do they still have 50% each for inheriting HD?
Mel, Young Adult, Greece
A. Dear Mel,
Thanks for the email.
If they are clearly dizygotic, then they each have a separate 50% risk, as you said in your email (exactly the same risk as non-twin siblings).
Sometimes there is a question about whether twins are identical or not, but there are ways of finding this out without necessarily testing the HD gene.
In some cases, the siblings are so clearly non-identical that “identicalness” testing is definitely not needed (for instance, they be one male and one female).