Breast cancer gene found in French- Canadian, Polish 'founder' populations: study

I guess my question is why? Is this the result of a small population that had been "poisoned" (if you will) by a few people with this mutation? Or is it because the gene was prevalent in the general French and Polish populations from which the "founder" groups were pulled? I suspect the former, but I do not *know* that. If the latter, has the prevalence of the gene been "watered down" in the general populations through immigration?

The study published Monday in the journal Nature Genetics involved more than 25,000 women with and without breast cancer within the French-Canadian and Polish “founder” populations, which have similar genetic profiles.

”This study showed that studying specific founder populations like Polish and French-Canadian women is an excellent approach for identifying disease-associated genes,” said Dr. Steven Narod, director of familial breast cancer research at the Women’s College Research Institute.

You see, this is why I love science. I know it was said in a different context, but as Mark Twain said: "There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact."