Nope-- I'm sure the world is full of dark-skinned people of African descent (hereafter referred to as DSPoAD-- sorry that "dispoad" starts with "dis-" and rhymes with "toad," but "dark-skinned people of African descent" is a handful to type and, seriously, if you're going to be offended by that, you're probably going to be offended by anything. If it hurts you, feel free to massage the hurt by calling me an ignorant hick-- you won't be the first.) who have autism spectrum disorders.
The DIAGNOSIS rate is lower for several reasons:
1) The "soft bigotry of lowered expectations." A DSKoAD* who makes OK grades, fails to follow some instructions correctly, and struggles with social interaction is "doing OK" in a lot of teachers' opinions, either because they automatically expect less of DSKoADs (what you'd get in wealthy or poor predominantly white places), they're terrified of being accused of racism if they say anything negative about a DSKoAD (what else you get in wealthy or poor predominantly white places, especially in very conservative or very liberal districts), or because they just don't notice in the middle of all the bigger fish they have to fry (what you get in urban and suburban ghettos, and also in poor districts where resources are so thin that they have to be allocated for kids that are REALLY in trouble).
2) Poverty. Whether we like to admit it or not, the legacy of slavery and the cultural dissolution it brought with it, followed by the "set 'em free and then ignore 'em" policy that was Reconstruction, followed by Jim Crow and his buddies definitely didn't do DSPoAD any favors, basically anywhere in Europe or any country that started out as a European colony. What that's accomplished, sadly, is a poverty rate so high it's SICKENING.
It's hard to break, too. It's hard to value education when you're struggling to put food on the table. It's also hard to value education when, for generations, what educators have taught you is that your people are lesser. The same thing has happened to Hispanics, Native Americans, Australian Aborigines, and poor Appalachian and Ozark whites.
It's hard to break out of poverty, when breaking out of poverty means leaving your home, your family, your friends, your culture, your people, and basically everything you've ever known and loved behind. Trust me-- I was born a poor Appalachian white girl. Now I'm an upper-middle-class white woman from Appalachia who is sort of kind of politely but grudgingly welcomed when she goes home to visit-- and I don't belong in upper-middle-class white culture either. Native Americans have a term for this-- "neither wolf, nor dog."
The upshot of that ramble is that, for all kinds of very good reasons, people who start poor tend to stay poor. And it's bloody hard to get access to the kind of diagnostic tools that can find all but the most severe cases of Asperger's when you don't have the time, the energy, the education, and above all the material resources to make a pest of yourself and pursue the most cutting-edge diagnostic tools.
Hell-- it's bloody hard to get too bent out of shape to raise a stink in the first place about a kid that's doing sort-of OK and sort-of NOT OK when you're working two or three part-time minimum-wage jobs then coming home, worrying about the housework and how you're going to feed everybody, panicking over the bills you STILL can't pay, then falling into bed and trying to get a FEW hours' worth of something like sleep before you have to get up and do it all again. It's bloody hard to do it when you've been drawing unemployment/SNAP/AFDC/SSDI for so long that you've given up looking for a job, given up on yourself, given up on your life, and you're just trying to get through each day without letting the depression that's gathering up around you pull you down and drown you or starting to deal drugs and hot property just to feel like you have SOME agency in making your own way, too.
My son and I would both just be up s**t Creek if we hadn't landed 1) near Pittsburgh (which has a hospital affiliated with a major university that just happens to do cutting-edge research in neuroscience), 2) with some of the best insurance available to civilians in the US, 3) with the education to do the research and find the connections to get to the right people, 4) with an educated, self-aware Aspie in the family, and 5) with the blessing of A HELL OF A LOT OF BLIND GOOD LUCK.
We HAVE all that-- and it's STILL up in the air whether we're going to find the right diagnosis, the right help, and the right tools to pull out of ASD, PTSD, MDD, GAD, whatever alphabet-soup combo he turns out to have, and the rest of it. And we're wealthy educated white people with every advantage our social standing can possibly confer and incredibly good luck. Sunbeams are filtering down all around us and angels are singin' in the background-- we're THAT f*****g ADVANTAGED-- and we're STILL struggling.
3) Stigma. It's bad enough everywhere. It's even worse among poor rural whites, conservative Abrahamic religions (Christianity, Islam, and Judaism), and American DSPoAD communities.
4) Suspicion. NOBODY wants their kid to end up with A Diagnosis. It's even more upsetting when you're among a population (Hispanics, ethnic-minority whites, Aboriginal Peoples, DSPoAD, ethnic Jews, et al) who have a clear and present reason for believing that "They" are out to get you. You tend to avoid seeking out help, when help could just end up giving "Them" one more reason to come after you.
There's probably more reasons that I haven't worked out.
The upshot of this dissertation, dear one, is that you are DECIDEDLY NOT ALONE.
*Dark-Skinned Kid of African Descent
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"Alas, our dried voices when we whisper together are quiet and meaningless, as wind in dry grass, or rats' feet over broken glass in our dry cellar." --TS Eliot, "The Hollow Men"