How can there be a difference of 3 repeats in the test?

Q. Hello!

My dad has got the HD Gene. They always take two blood samples. The counts of the mutant gene were the same in both cases. But for the normal gene there was a difference of 3 repeats. How can that be? Can the count of the mutant gene also be insecure?

Thanks

Efa, 18, Germany

A. Dear Efa,

Thanks very much for the message. Differences in tests on the same person of more than 1 repeat are very rare indeed. We know this because most of the people on the big European follow-up study (called REGISTRY) have been tested twice; once at their local lab and again as part of the study. This might be one of the reasons for taking two samples (if they are very different, then they can be re-examined).

Best wishes

Hugh