January 23, 2012
Low Birth Weight Triples Autism Risk
Why not a higher autism correlation between twins? birth weight is a key factor in determining autism risk.
EVANSTON --- Although the genetic basis of autism is now well established, a growing body of research also suggests that environmental factors may play a role in this serious developmental disorder affecting nearly one in 100 children. Using a unique study design, a new study suggests that low birth weight is an important environmental factor contributing to the risk of autism spectrum disorder (ASD).
“Our study of discordant twins -- twin pairs in which only one twin was affected by ASD -- found birth weight to be a very strong predictor of autism spectrum disorder,” said Northwestern University researcher Molly Losh. Losh, who teaches and conducts research in Northwestern’s School of Communication, is lead author of the study that will be published in the journal “Psychological Medicine” and is now available online.
But let me quibble about terminology: For millions of people on the autistic spectrum their autistic minds are not a disorder. Many are quite high functioning and happy to be on the autistic spectrum with the intellectual advantages they gain from their modes of thought. I think the problem is that too much cognitive variation has gotten subsumed under the autism label.
Still, this finding on birth weight is important.
The researchers found that lower birth weight more than tripled the risk for autism spectrum disorder in identical twin pairs in which one twin had ASD and the other did not.
My guess (and I expect this to become crystal clear in under 10 years due to cheap DNA sequencing technology) is that many genes that cause some aspects of autism were selected for. There was an adaptive advantage to a sort of specialization of cognitive labor. Genetic influences on a phenomenon that occurs a fairly high rate of incidence usually point to something that was selected for rather than developmental error or relatively rarer purely harmful genetic mutations. Highly maladaptive traits rarely get selected for.
There's some overlap between autism as a result of genes selected due to their reproductive advantages versus events that go wrong in brain development. That overlap has made clear thinking about autism harder to do. Given that clear thinking about the mind is hard to do in general that's not too surprising. But on the bright side, advances in psychometrics, neuroscience, and genetics are going to usher in a new age of understanding of the human mind and along with it will come a much more nuanced view of autism.
By "low birth weight" do they mean premature or underweight at full term (or both)?
After recently reading Jon Ronson's "Psychopath Test" I've been thinking ideas similar to your comment on the range of cognitive variation.
Of course, at our best a diagnosis is based on our honest attempts to help someone who is suffering. Sometimes, however, variation is labeled with an diagnosis for reasons unrelated to brain structure, psychology, or genetics. Thinking about young children, some reasons may be that the diagnosis can mobilize additional resources from a child's school, drug companies can sell more product if a diagnosis is covered by insurance, students may be given more time to take tests, and other perverse incentives. By making a diagnosis a threshold for certain social benefits which clearly some students need, but others who need them less may want, there will be pressure to move the threshold for all sorts of diagnoses closer and closer to neurotypical. I think mass-customization in education may play a roll in addressing these issues in the future.
Wouldn't medical treatment also be a factor? Low birth-weight babies are generally in the ICU initially, where they don't have the touch & bonding that full-term/size babies have. It would make sense that they would have a harder time with physical touch when they're older then, no? Not all autistic kids are smarter, but most of the ones with above average intelligence have above normal activity in the memory centers of the brain. So maybe the lack of physical intimacy contributes to more growth of the memory-related areas of the brain during early development.
This kind of discordant twin finding doesn't do much to support your genetic hypothesis, though. Looks a lot more like developmental pathology.
There's already plenty of evidence supporting the genetic base of ASDs, bbartlog. That has been coming in since at least 1943, for those who would listen. It was not politically acceptable in the US to acknowledge it till about 1990. The key here is that Autism is still a basket diagnosis, and genetic combinations that might not produce recognizable symptoms, by perhaps a single SNP, could be pushed into it by something like low birth weight that also affects brain development.
Indeed, I find that when I get a low blood sugar from diabetes, the accommodations to neurotypical behaviors that I developed over the years slip away, and my Asperger Syndrome become far more evident to neurotypical friends.
I think autism, as a category, as it currently stands (although it did not historically), includes both
- people who have lost or impaired of certain forms of brain function, not with any gain of function elsewhere, simply for the same kinds of reasons people have low g
- people who have lost or impaired of certain forms of brain function, as part of a tradeoff for other forms of function
and co-existing with this, some of these people
- may have high general intelligence and brain function, to the point where even the bits where they have "impaired" brain function aren't really impaired compared to the average (see the so called high functioning autistic)
- while others may have very low general intelligence and brain finction
Now this means there is a difference between
- the people the high functioning autism activists (often with identity politics, a disagreeable personality and a grievance against the world at large) want everyone to focus on, who are the people who both have high g and who have autistic traits as a tradeoffs,
- and who the parents of severely disabled autistics want everyone to focus on, the people with low g and autistic traits without any pluses (their children), who were the original group the autism definition was constructed for.