Thursday, September 27th, 2012
The scientific paper describing the increases in DNA mutations that correspond to increases in paternal age – published last month (click here to see my discussion of the scientific aspects of the study) – has generated lots of discussion about the need for reconsidering how age may affect paternity and fathering. See, for example, Lisa Belkin’s thoughtful discussion about the utility of men hearing the ticking of a biological clock.
It can be argued that the biological role of fathers, with respect to age, has not received as much attention because we think of the biological clock as primarily representing the probability of being able to reproduce – with those effects being, of course, most pronounced for females. What is now emerging into the public awareness (based on a number of studies conducted over a number of years) is that paternal age – like maternal age – may be associated with an increased risk for passing on certain genetic risk factors that may confer risk for disorders.
We may get to a point where there are risk charts that quantify the increasing probability of paternal mutations that correspond to age and associations with risk for various disorders in offspring (much of the interest right now comes from the potential links between paternal age and autism). Consider, for example, this chart showing the increasing probability of having a child with Down syndrome as predicted by maternal age.
The complexity here is that prospective parents have to consider, in most cases, probabilities rather than certainties (unless there is a screening for a known genetic disorder that runs in a family). Is a 1% chance, versus a .5% or a .01% chance, enough to change someone’s family planning? This is tough to answer. For some people, it may be highly influential. For others, social and personal factors may override such probabilities. What is clear is that genomic research will continue to deliver more and more probabilities in the future (near and far) – and the information that is generated will pertain to both prospective moms and prospective dads. And that prospective parents will have to make more and more complicated choices that are partially (but not fully) informed by genomics.
Statistics and probability via Shutterstock.com
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Friday, August 31st, 2012
You may have read recently about a study that links the age of a father with the risk for autism. While there is some real science here to report, there is also the possibility of making too much of all this. So let’s break it down.
Prior studies have suggested a link between the age of a dad and the risk for autism – as a dad’s age increases, so does the risk. The new study (published in the journal Nature) reports on a possible mechanism for this: it involves the number of genetic mutations that are passed on to a child. Click here to read a summary in the journal.
There are a few underlying ideas that are important. This line of research is showing that genetic mutations are much more frequent in a father’s sperm than in a mother’s egg. This makes sense, in that the sperm are produced throughout the lifespan in men, but women are born with their lifelong supply of egg cells. The authors of the Nature paper suggest that there is a steady increase across decades in a man’s life – so that when you are 40 you will produce more mutations than when you are 30 (and so on).
What’s the connection with autism? Well, right now it is a very indirect association. There is lots of interest in the idea that spontaneous mutations play a role in causing autism. Lots of papers have been published on this over the last few years. So the thinking here is something like connecting the dots – if spontaneous mutations are involved in the etiology of autism, and a dad’s age is a primary source of such mutations, then perhaps there is a link.
All that said, keep in mind the following:
1) The new study published in Nature did not provide any direct association between the mutations and autism
2) The assumption is that many of the mutations are harmless (and in fact somewhat normative)
3) There is, at this point, no clinical screening process to determine or suggest that a father passed on a mutation to a child
4) There are, at this point, no genetic counseling implications
Perhaps most importantly, there are lots of factors that contribute to the etiology of autism. There are certainly heritable factors that go beyond spontaneous mutations. And there are undoubtedly non-genetic factors as well.
So where are we at? At this point, spontaneous mutations are just more potential pieces of the puzzle with respect to the etiology of autism. They will continue to be researched and, hopefully, may in the future reveal more about the underlying biology of the disorder. But it’s way too early to begin to transfer the basic science into diagnostics and prevention – and too early to know what role spontaneous mutations will be shown to play in the broader context of multifactorial influences on autism.
DNA image via Shutterstock.com
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