I can't source the study, as it was referred to rather darkly as one that had attracted heat, but with the promise that more is coming over the next few years, but I will explain it because it says something about the changes in my assumptions over the years.
The study was in cognitive genomics, so you might already guess where the controversies might arise. In the last two decades there has been enormous work done discovering Mendelian Disorders, single-gene mutations that have deleterious effects. A researcher looking at larger genomic data noticed something odd. There were occasional people with a Mendelian disorder related to IQ who nonetheless had average IQ scores. Pulling them out for further studies, along with their parents and siblings, he found that they had two parents of 130+ IQ, with siblings clustering around that higher range rather than the national average. The children had IQs two standard deviation below their parents, which in ordinary circumstances would result in children with deficits, requiring special attention at school. But with these parents...
My assumption 35+ years ago would have been that it was the good educational environment of those parents - reading to the child, proper nutrition and attention, better schools. That would still be the assumption of many people, and news stories about such research would leap to that conclusion as well. In fact, you can get into some trouble if you reach any other conclusion. Ask Charles Murray about that.
But among those who are studying this more closely, the idea of mutational load , more commonly associated with studies of immune diseases, is quietly coming into favor. The researcher anticipated that and dug deeper. The assumption that those IQ 130+ parents consistently provided good, nurturing environments was not entirely solid. As soon as we say that out load we all recognise that of course that was a terrible assumption. We have a prejudice in that direction, but once held up to the light we all think of specific examples of contentious divorces, alcohol or drug abuse, entire irresponsibility of high-IQ* individuals, or terrible circumstances involving accidents or tragedies that send a child to another place to be brought up.
The researcher thought this was powerful evidence that the lack of negative mutational load was somewhat protective, even against serious cognitive deficits. Apparently he has gotten some pushback at his own university from "other departments" - hmm, I have a short list what those might be - about the implications of this, so he is waiting until he has more results before inviting that amount of misery on himself.
My assumption has reversed. I am in no way a researcher or an expert in anything near this field, though I know well more than average. When I heard about the Mendelian Disorders related to IQ still resulting in average intelligence, I now think "What else is happening genetically?"
*See, this is why "smart" means something else, that has some overlap with IQ but is not synonymous.