This is an old theory now that has not been validated to my knowledge.
I agree – I am diagnosed with high-functioning autism, but it's a complex condition that's unlikely to be explained by a theory like this.
I didn't take any additional B vitamins until I developed cobalamin malabsorption in my 50s, caused by long-standing gastritis. The B12 injections, and the high-dose methyl folate that I took to help it work, did address the deficiency very successfully. There was no change in my autism symptoms before I developed B12 deficiency, during the period when it was at its worst (and highly symptomatic), or once I'd got it under control with these additional supplements.
I'm not sensitive to methyl folate, but as I don't like taking unnaturally large doses of anything, I reduced it to a small dose just once a week as soon as my B12 level had normalised. Neither the large nor the small dose seemed to makes any difference to ME or autism – at least, not one that I could detect.
It might be helpful to be assessed for autism,
@SmokinJoeFraz93, so that at least you know what you're dealing with. Like many high-functioning women, I wasn't diagnosed until I was an adult – hundreds of thousands of us in the UK alone were missed, simply because no-one had defined how it presents in girls. Because of this, assessment services for adults are becoming more available, and of course they're not limited to women.
I decided to ask my GP how best to proceed with getting an assessment. She suggested I write a one-page potted history of the difficulties I experienced as a child and an adult; she passed that the our local autism service, who then invited me for an appointment. I hope you're able to get some answers.