Wednesday, September 06, 2006

Older Fathers and Autistic Kids
I'm sure many people heard about this yesterday, as I did when I woke up, but both the BBC (read) and NPR (listen) were reporting on the study that came out in this months Archives of General Psychiatry* showing a possible link between paternal age and the likelihood of having a child born with an autism spectrum disorder (ASD). It was, of course, all the buzz at the office, so I used my handy academic connections to get my hands on a copy of the actual article.

Though fairly short, it is fascinating. The first thing I noticed was that Isreal has pretty much the ideal set-up for a population study of this sort, because everyone, and I mean everyone (except orthodox Jewish women,) is evaluated and documented by the draft board, with official and consistent diagnosis codes noted in the file, as of age 17, which makes for robust diagnoses, and these records are in turn linked to those of the parents. In addition, everyone in Isreal who receives services for an ASD is registered with one central non-profit agency. A researcher's dream, clearly.

Anyway, the point is, the research team ended up with an enviably large cohort of children with ASD born in 6 consecutive years during the 1980s. They analyzed the data with just paternal age as the predictor, and then again with adjustments for year of birth, socioeconomic status, and maternal age. In both cases, paternal age showed as an increasing risk factor. Perhaps the most intriguing finding, though was this:
The association between paternal age and ASD risk is evident in male and female offspring... However, the male-female sex ratio in the offspring with ASD of fathers younger than 40 years (5.6:1.0) was noticably higher than the sex ratio in the offspring with ASD of fathers 40 years or older (2.3:1.0).
Though the researchers note that there was not a large enough sample size for really robust analysis, "[t]hese numbers... are intriguing nevertheless as they suggest the possibility of a distinct etiology for ASD that is more prominent among offspring of older fathers and that pertains equally to both sexes."

In the comments, they go on to suggest some possible genetic reasons behind this, specifically de novo spontaneous mutations and paternally expressed imprinted genes, which I don't understand enough of the background for to provide a nicely synthesized explanation. However, the earlier note about a possible distinct etiology for ASD found in offspring of older fathers jives with a lot of the thoughts I've had, and that I've heard others more professionally related to the field express, that there is probably no one cause for autism to be found, but many. There may, in fact, be numerous kinds of autism, but we don't know enough about the underlying causes of any of them to be able to tell them apart. This could also explain why some children with autism seem to go through a regression phase in early childhood, while others never do; why some seem to respond to special diets, while others don't; etc., etc. It's a fascinating possibility to consider. It'll be interesting to see what researchers continue to find out in the future.

*Reichenberg, A. et al. Advancing Paternal Age and Autism, Arch Gen Psychiatry. 2006;63:1026-1032

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