This gets brought up often and while true isn't very useful. We know jumping out of plane is dangerous because we have a good understanding of the physics and we have many many comparable examples (jumping out of buildings etc). We understand the mechanism of action of parachutes, so we also know for example a tiny little parachute made of paper towel won't work, and we don't need to test it to know that.
Do we understand the cause of autism or how this supposed cure works?
The key is effect size. We didn't know the exact method of action when we started injecting comatose diabetic children with insulin, but when the coma patient sits up and starts chatting with you, you can establish that a drug is effective with very small sample sizes.
Sure, but even there you need some reasonable sample size. i.e. a sample of 1 won't be sufficient and more importantly it needs to be reproducible. Inject 1 patient and they wake up, but if you inject 10 others and nothing happens and it may not be effective (not that it's definitely not effective). This would require a then a larger sample size.
Autism isn't as cut and dry as this. Falling out of planes and diabetic comas are truly black-and-white outcomes, but ASD assessment involves behavioral testing of social and verbal ability, which has high variability between and within individuals. The linked studies about folinic acid are not finding a binary conversion of of ASD kids from non-verbal to verbal, rather they are detecting X% increase in Y behavioral test, which is subtle and something that is found with behavioral treatment. I would love to live in a world where we discover a treatment for ASD that is as clearly successful as insulin for diabetes, but we're not there yet.
Do we understand the cause of autism or how this supposed cure works?