My son is the third or fourth generation to be likely-diagnosable, for example.
Currently-middle-aged parents without intellectual disability had almost zero chance of being diagnosed as children, because when we were kids autism was defined such that you usually had to be nonverbal or intellectually disabled to qualify.
A very commonly-reported experience is for parents to be diagnosed after their children are diagnosed.
There are some evidence that hints to genetic factors. For example, we know that boys are at much higher risk than girls, but we don't know why. Similarly, we know that older parents are more likely to have autistic children—but again, we don't know why.
Also the boy/girl factor could be explained by different behaviors, so different exposures.
Not saying I know anything about this, or that this is the case, just that the increased family risk and boy/girl risk doesn't mean it is genetics.
That's correct, but looking at concordance rates between monozygotic (identical) and dizygotic (fraternal) twins demonstrates that there is at least a partial genetic connection.
Identical twins share the diagnosis in 77% of cases, while fraternal twins only share the diagnosis in 31% of cases.[1] Given that identical twins share more genetic material, the conclusion is that autism has a genetic component to its incidence.
That said, most research on the subject, including the paper I'm citing, establishes that there is most likely a dual nature-nurture component. In particular, this study was conducted on twins within the same household, so the genetic component would have been augmented by shared environmental factors.
The implication seems to be that the parents also exhibit traits of the autism spectrum, so it's hardly surprising that their kids would do the same.
Despite the quantity of autism research, most of it is quite bad and not that helpful on questions like this.
"Environmental" can include "parenting", but in this case the distinction is between "got it somehow from autistic-leaning parents" vs got from something else.
Also, the claim that autism might be somehow learned from parents is extraordinary and not widely claimed or supported by existing evidence. It was a discredited theory of the past though, that "cold" parenting created austism.