Dr. Blakelys lab has produced knock-in mice with the rare SERT variants described, and they have exhibited the behavioral and biochemical markers of ASD. It's actually a very remarkable finding. They also saw a reduction in ASD symptoms by pharmaceutically blocking the offending inflammatory pathways.
So I think at-least for the tiny fraction of ASD patients with these rare SERT variants there's actually a chance that they are a major driver of the disorder. Regardless it provides a tantalizing look at some of the upstream pathways that could be involved more generally.
I think we're going to find the disorder is very heterogenous and there will be many different subtypes and pathways involved.