I read a provocative article at the BBC on a twins study that provides some evidence for something that I’ve been wondering about for some time:
Autism is caused by genetic make-up in 74-98% of cases, a Medical Research Council study of 516 twins indicates.
The King’s College London team said 181 of the teenagers had autism, but the rate was far higher in the identical twins, who share the same DNA.
The researchers told JAMA Psychiatry tens if not hundreds of genes were involved, and they do not rule out environmental factors entirely.
Both twins in each pair had been raised by their parents in the same household.
which is the role that genetics plays in autism. Over the years lots of candidates for the “cause” of autism have been put foreward. From the 1950s through the 1970s (at least) childrearing practices were blamed, the “refrigerator mother” (look it up) hypothesis. That was succeeded by the suggestion of possible environmental factors. Everything from preconception parental behaviors to vaccines have been blamed at one time or another.
In my view the cause of autism is probably multi-factorial but it’s going to become increasingly difficult to deny that genetics plays some role. The follow-up question is why has there been an up-tick in the diagnosis of autism? The article’s explanation is that’s an artifact of physicians making more diagnoses rather than more frequent occurrence but I have my doubts. I can’t help but wonder if, unwittingly, we’ve been breeding selectively for autism.
That is the way evolution works, after all. Traits that were favorable in the parents are reproduced. If those traits are amplified in the offspring, that can result in the amplified version of the traits being unfavorable in them.
I read an article a while ago that advanced an interesting hypothesis re autism: It seems that young children, very young children, have a superabundance of brain cells. This superabundance aids in the acquisition of language, socialization, and so on (acc. to the hypothesis). As children age, these superabundant brain cells die off. Except in the case of autistic children — they still have them. This leads to a hypersensitivity to stimuli that non-autistic children don’t have. Autistic behavior is a response to the resulting stimuli-storm.
Therapists who diagnose neurodevelopmental disorders are generally not adhering to rigid categorical ideals, they offer a diagnosis when it appears that it will help the client. If Ritalin eases symptoms, the child is confirmed to have ADHD.
Over the last 20 years, the benefits of early intervention for autism have been recognized. This means the therapist is seeing children under age three that parents fear might not be developing “normally.” (Parents always have these fears). That places the therapist in a fairly preposterous position that they would normally reject, but the potential risk/benefits are too important. (My wife was excited a few years ago with studies that tracked the child’s eye movements while watching a film, i.e. whether the child looked at faces or dead-center in the screen) The therapist may end up looking mostly at parental risks, i.e. age of the parent, exposure to pesticides or chemicals, obesity. Diagnosis through abundance of caution. Either the treatment worked or may never been needed in the first place (or perhaps some point in between).
Part of the selection issue is that parental age is a significant factor, which would increase mutations. Deferred parenthood corresponds with more education.