[cSoze]

The antagonistic pleiotropy theory actually advocates exactly that inverse correlation, more investment into young years for increased reproductive fitness at the expense of worse later years.

Further, I suspect that number of kids or even just a binary having kids or not would have a direct effect on BMI in old age. More kids > less time to excercise > compounded over many years. There's also a known correlation between educational attainment and number of children in the literature which is generally hypothesized to be causal.

I have concerns about the validity exactly because of the expected tiny effects. Polygenic traits with extremely high heritability (height being the prime example) top out at 10% of variance explained even when considering all alleles. That just highlights the need for better phenotypes and multi generational typing. I think it's Botstein who I've heard advocates for more time points over more replication when given the choice.

[aab0]

> The antagonistic pleiotropy theory actually advocates exactly that inverse correlation, more investment into young years for increased reproductive fitness at the expense of worse later years.

Which would be great if you had any evidence that BMI is largely influenced by such antagonistic pleiotropy. But since BMI is not a disease like Alzheimer's, it doesn't even have prima facie plausibility. This shouldn't be hard: does low BMI in youth predict high BMI at middle or old age? I've never seen any result ever hinting at this, and no one believes that.

> I have concerns about the validity exactly because of the expected tiny effects.

Yes, it does make it harder, but fortunately, that's what we have polygenic scores for. Do you have any power analysis suggesting that the sample size here is inadequate?

> Polygenic traits with extremely high heritability (height being the prime example) top out at 10% of variance explained even when considering all alleles.

Totally wrong, where did you get this idea? The height polygenic score is at >>10% of variance (see Wood or http://ije.oxfordjournals.org/content/45/2/417.full ) and BMI polygenic scores are already at 10% and will go up since all the twin and GCTA estimates indicate larger heritability than that.