I got a bit frustrated when following the articles on the Unz Review, you know these alt-right guys, lots of fun to read even if does not agree with them. Anyway, there are several writers who come up with the heterozygote advantage as an explanation for Ashkenazi intelligence. Surely you remember the claim in the paper by Cochran, Hardy and Harpending from 2006 that nobody has been able to demonstrate. I have one time done some similar calculations from recursion equations and this idea of a heterozygote advantage simply does not work mathematically. You need a different pump to get lethal gene alleles stay in a population. It is not only this Ashkenazi thing, it seems that medical or genetic researchers propose heterozygote advantage too easily without checking the mathematics, if there is a steady state for their values.
So, I wrote a paper on this in a purely mathematical way. It is easy math. Everybody loves recursion equations. I show that recessive lethal alleles do not remain in a population because of heterozygote advantage. They could, there is a steady state, but the ratio between the carrier frequency and the disease prevalence show that it is not that mechanism.
I also discard the idea of a founder effect and genetic drift. It just cannot explain why Cystic Fibrosis has stayed for 52,000 years, as Wikipedia claims. And they are always right, or almost, depends on the topic. Very often they are.
Then I propose a pump mechanism which seems to work. It is just a simple mechanism: some families tend to have many children from generation to generation. It does boost recessive lethal alleles. The recursion purges lethal alleles out in some 1450 years, but the pump puts them back in.
So here is the paper.