I know those stats about dx with ASD in non white communities. I did an essay of ASD DX for my MA Autism on that and used them.
They were American stats and explained by a combination (IMO and certianly I passed the essay) of access to ehalthcare amongst that community (I can easily send the essay on as I did cross reference the stats on poverty etc) and different attitudes to healthcare.
Squid ds1 attends an ASD Base and they studied Einstein and his ASD yesterday; I get why, they were talking about things that make you special despite a dx, but absolutely- there was no DX! I've seen his name claimed for AS (hardly if he did not talk until 4, breaks dsm criteria), Dyslexia......
Lots of research with High Res MRI scanners suggest brain differences in children with ASD* but the cost of high res MRI prevents that being used as a wide scale diagnostic test.
I am aware of the oxytocin research but also that something having an effect on something does not claim a cause, it may well be a medication: the biggest single factor in ASD seems to be a genetic history (will outline ours in a minute), but current thinking amongst most scholars is that there is no ASD as such (this is where the * comes in), just a great many conditions sharing a core presentation and they will gradually be broken down into groups of disorders which might help understanding.
Now my research is on ASD and empathy, there is some really intriguing research (and I do NOT mean Baron-Cohen's zero empathy stuff which may well turn out fab but is being sold in media as linking ASD with evil) and I strongly beleive that variation in empathic ability (not just level, type) are related to ASD outcome. Oxytocin might well affect this I guess and my MA Diss is being done as a trial study in case I ever get PHd funding, will be something I can discuss thanks. fab idea!" 
Apols for lack of paragraphs, Mn seems to having a strange blip and I can't get any to work- and typos- SD ds4 on my lap wriggling!
Right my family; strongly matriarchal on both sides, but most esp. paternal- one of thsoe famillies where the men got pissed and the women ran everything. Still matriarchal tbh- me and my sisters- well we married some brave men!
DS1- diagnosed AS, attends ASD Base for comp
DS2- MS, school say ADHD, Dyspraxia, dyslexia- Gp says I don't do that wooly stuff so no dx's
DS3- fairly sever (verbal bbut will never be independent) autism, attends general SN Base
DS4- beinga ssessed for ASD; has dx of speech dealy but clear ability so fits HFA criteria
DH: severe dyslexia, history of depression; MIL OCD; FIL severe dyslexia; my Grandad clear autism but HFA so no dx due to age (94); Uncle high likelihood of AS, has been in Psych care on and off all his life, no dx that we know of but he won't tell anyone anything,first care episode following death of his dd; Mum no dx but says she is fully aware of having AS and certainly that fits her life so far and how it ahs panned out- eg high ability but no social skills or friends, struggled to keep jobs, depressive history. Me- kn ow i could fit AS x but won't get assessment as I know diagnostician through uni and seems woerd, hasbeen discussed informally with her though and also with my uni specialist who agrees.
*But mainly my point is that it's not going to turn out AD has a single origin- we already know that due to it's links with Downs Syndrome, some cases of retts, encephalitis,
so whilst there may be some truth in many explanations there isn't one universal truth*