>Low iron intake significantly interacted with advanced maternal age and metabolic conditions; combined exposures were associated with a 5-fold increased ASD risk.
Maternal age and iron intake aren't genes. Neither is folate:
Their final analysis had N=209; is that a large enough sample considering the prevelance of ASD? Or does their use of the SRS scores (as opposed to a boolean "on the spectrum") get around that?
My completely unscientific opinion is that human genetics in general hasn't changed much in recent years, compared to the changes in our lifestyles. If you had to pick one as the cause of an increase in autism diagnoses, the change in lifestyle seems more obvious.
This opinion isn't based on any concrete facts, so feel free to change it.
As a disorder, it's quite new, so it's quite natural that the increase of diagnoses increased in the past few decades.
Also, if I'm not mistaken, the research behind genetics of brain issues is quite straightforward. It's thanks to twins - we analyse occurrence in monozygotic and dizygotic twins. If there is far higher correlation of the disease in monozygotic compared to dizygotic, we know it's genetic.
"Concordance in ASD diagnosis ... is observed in monozygotic (MZ) twin pairs at rates of 60-90%, whereas rates among dizygotic (DZ) twins are estimated at 3-31%."
I think it's more likely that we are just getting better at diagnosing it, and the autism spectrum has not only existed throughout human history, but a large minority of our most celebrated artists, scientists and mathematicians were likely on the spectrum to a degree or another.
Except that is not true.
We know from texts that if anything old "geniuses" were not autistic, but they were on the bipolar spectrum, or more generally on the affect spectrum ( mood disturbance ). Winston Churchill for example is famously bipolar. Many texts refer to feeling an overbearing sudden sadness, as in bipolar depression spectrum.
Autism and schizophrenia are so horrible because they are not on the affect spectrum. So in a historic view autism is indeed a new and a modern madness.
I would recommend the book "The Master and His Emissary" by Iain McGilchrist.
I can't find similar data for age of the father at birth (or rather conception), but the human clinical geneticist I know always emphasizes that age of the father is just as important.
Your intuition is assuming that rates would increase because mutations enter the general population and then spread through that population at some possibly small rate.
However, the prevailing genetic explanation for increases in autism prevalence rate is that mutations appear de novo (out of the blue) in a parent, and then are passed down to the proband with the disease. The de novo mutations in each case are different, more or less.
The reason that prevalence is increasing under this model is because there is is something that is increasing the rate with which the de novo mutations are passed onto offspring.
This reason is age: de novo mutations occur increasingly with age in germ cells, and if germ cells become offspring at later ages, you will see an increase in prevalence.
Studies suggest that spontaneous mutations in sperm become more common as fathers age, because of age-related issues, and these sperm with mutations are more likely to lead to autism. Because fathers are having offspring at later ages, autism is increasing in prevalence.
Maternal age is less strongly related because egg cells are formed earlier in development.
FWIW, I agree there's probably lots of environmental influences, but I don't think that's the only thing.
Some experts in the field think that we've improved our ability to diagnose autism and diagnose it early (as this article also mentions). That's been one explanation for the increase in autism diagnoses. I agree that genetics probably haven't changed enough to account for the entire increase in diagnoses, so there's a counter-explanation.
You have to keep in mind that just because diagnoses of autism have increased doesn't mean that rates of autism have increased. I've noticed diagnostic substitution in my own family.
