Genes are useful because they are far more fixed and they are far easier to measure than many other things that could be measured.
>"I think they’re trying to say “it’s not the mother’s fault the kid just has bad genes.”
They're saying non genetically inherited material, such as mRNA or proteins, from the mother was shown to have little impact in their study.
> In the real world there are non-genetic causes behind almost all of the symptomatic presentations of children medically-cursed with the diagnosis of “Autistic”.
The causal nature of any complex biological state such as ASD is almost always varied and emergent from many sources and attempting to understand them is useful. It is especially useful to look at genetics because it is (relatively) cheap to get a person's genetics and painless - whereas studying the microbiome is much more difficult and expensive. even the review paper you link to - which has precious little actual research on autism and the microbiome stating
>And in autism spectrum disorders (ASD), there are hints that the gut microbiome may play a role. Studies of fecal DNA extracts have found Clostridium or Desulfovibrio clusters over-represented in children with gastrointestinal complaints and ASD as compared to children with similar GI complaints but typical neuro-behavioral development32–34. Furthermore, clinical improvement has been reported anecdotally in children with ASD who develop fever35, receive oral antibiotics36, or ingest probiotics37, all of which are likely to alter the gut microflora. While these initial studies are promising, they suffer from small sample sizes, in part due to the laborious, conventional, culture-dependent techniques used to identify bacterial species