Allele in Hardy-Weinberg deviation

[nta74]

Hi,
I am not an expert in the field of population genetics and I have a question about some recent data we have.

We see one allele variant in HW-deviation in 2 unrelated populations (chi sq. 12 and 9, respectively), but only in disease cases (we're studying ALS, we tested 200 controls and 200 disease cases for each population).

What could be in your opinion the possible interpretation of this observation? Is the allele under selection in the disease, or maybe a bottleneck effect due to small sample size?

Thank you in advance.

[LeBrok]

I'm not population geneticist either, but I would guess that our genetic knowledge is still too limited to give definitive answer to your question. Especially when control sample is so small and we don't have a clue how it evolved through past generations.
Neutral or mildly deleterious alleles could linger through millennia in populations, till replaced with a very fit one, or by other neutral due to population bottlenecking.
Sometimes genes have double functions. In this case it might have a second function which is very beneficial. Sometimes alleles are very beneficial only in connections with other genes' alleles, but alone are neutral.

All I got. ;)

[nta74]

Thank you for your kind explanation, I understand and agree!