Last week, the journal Nature published a paper titled "Risk of de novo mutations and the importance of the father's age to disease risk." As Paul Raeburn noted here at the Tracker, the resulting coverage focused almost entirely on whether aging fathers could be suddenly seen as a significant contribution to autism cases.
Perhaps that emphasis isn't surprising given the fact that autism is a high-profile condition and given that earlier stories had put more emphasis on the age of the mother. But, as science writer Seth Mnookin points out in a Monday post at New Yorker.com, the autism emphasis may have missed the real point of the study. Or to quote him on that point, "What was surprising was how that news, which one of the study’s lead authors described as “sort of a little bit of our side story,” obscured the implications of the paper’s main findings—namely, that the genetic health of the species is now facing a serious threat."
The key point, according to study authors, is that de novo (novel) mutations occur at a far greater rate in sperm than in eggs. Basically, this is because eggs turn out to be a fairly stable product in the human reproductive system while sperm cells are constantly dividing. So that as culture and medicine allows for older and older fathers, that result also allows for a greater mutation rate in aging sperm. A Nature commentary on the article, in fact, raised the possibility of a coming "decline in the mean fitness" of the human population.
Mnookin provides some evidence that such a decline may already be underway. And he raises the question of whether this should eventually become part of science policy discussions. It's a fascinating and important follow up to the original coverage and a reminder that when we, as science journalists, become too focused on the buzz-topic issues we run the occasional risk of missing the real story.
UPDATE - A couple days after I posted this, Seth put a Storify up at his blog at PLoS, detailing the response from genetics to his story via Twitter. It's called Twitter Awesomeness: I Get Schooled in Genetic Sequencing and you'll find it here.
---- Deborah Blum
Comments
Mnookin's Storify post has disappeared from his blog. Which is not only a bit of a mystery, it's frustrating. I wanted to see what geneticists said.
The point in Seth's piece comes from these words om your last sentence, that "more often than not mutations are deleterious." He quotes at least once geneticist who calls it scary to see the mutation rate ramped up in aging sperm. You're right, of course, about driving evolution but I think the fundamental question here is - driving where? (Note the Storify update I added though as geneticists also reponded to the piece).
Genetic decline? By increasing the number of mutations in the population, I thought one of the interesting possibilities of the work was that variation was increasing. Variation's not pretty, and more often than not mutations are deleterious or neutral, but in the end, it's one of the key drivers of evolution.