"Black women from East Africa had more than 3.5 times the odds of autism spectrum disorder with intellectual disability in their children than Caucasian nonimmigrant women."
So said the study results reported by Jenny Fairthorn and colleagues  (open-access available here) providing yet more evidence for the need for much greater scrutiny as to why children of immigrant parents from East Africa are seemingly at higher risk of 'more severe' autism than other groups (see here and see here).
Based on data from "Western Australian state registries" (yet again), researchers set about comparing autism prevalence with and without intellectual (learning) disability as a function of various variables: race (ethnicity), immigrant status and region of birth of mothers of children. The authors really drilled down into the details on immigrants according to their birth region in this study.
Results: from a study sample of over 130,000 mothers, some 1000 had a child diagnosed with an autism spectrum disorder (ASD) together with intellectual disability (ID) and nearly 350 with a child with autism without ID. The figures equated to something like 0.7% of the total cohort with a child with autism and ID and 0.2% of the cohort with a child diagnosed with autism but not with ID. Authors also indicated that: "mothers of children with autism spectrum disorder with intellectual disability were more likely to be 40 years or more."
Then to some important data: "After adjustment for demographic factors and compared to nonimmigrant women, immigrant women were less likely to have a child diagnosed with either autism spectrum disorder with intellectual disability or autism spectrum disorder without intellectual disability." This finding covered various geographic locations from which migrant mums came together with their race/ethnicity. That is however, aside from mothers from East Africa, and that "three-fold higher odds of having a child identified with autism spectrum disorder with intellectual disability." Authors added that "all autism spectrum disorder diagnoses in the children of Black mothers were of autism spectrum disorder with intellectual disability" and that all cases "were from mothers born in East Africa, with four born in Ethiopia and one each from Eritrea, Kenya, and Somalia."
The authors acknowledge that their categorisations based on race/ethnicity and migration status led to some quite small group numbers being analysed (including not including any participants from other parts of Africa outside of East Africa). They also drew attention to the fact that their participant group of children with autism but without ID was quite a bit smaller than would be typically expected in comparison to the group with autism and ID (see here).
But the results do paint an interesting picture and particularly with regards to those from East Africa, where they are in line with what has been previously discussed in the peer-reviewed and lay literature. The question of 'why' is probably going to be a complicated one as the authors suggested that "at least some of this difference could be the result of various factors leading to higher ascertainment of autism spectrum disorder in this group of children." They also qualify that statement by saying that they "cannot rule out the possibility of some biological risk factor, such as nutrition or stress" being involved which opens up a role for variables such as vitamin D exposure for example (see here).
Personally, I think there are a few additional research directions that might need to be considered, primary among them is to have a little more detail on what autism prevalence might specifically look like in various areas of East Africa and Africa in general. I know this is a bit of a difficult ask in places where resources are really quite scarce, cultures are different (see here) and practical efforts for population screening are hindered by politics and the like. Until however we have such data, alongside some other important social and biological information, science doesn't have any 'baseline' measures on which to compare and contrast when it comes to families emigrating from such places and the possible reasons/changes that could be involved in this process and pertinent to offspring autism risk.
 Fairthorne J. et al. Maternal Race-Ethnicity, Immigrant Status, Country of Birth, and the Odds of a Child With Autism. Child Neurol Open. 2017 Jan 12;4:2329048X16688125.
Fairthorne J, de Klerk N, Leonard HM, Schieve LA, & Yeargin-Allsopp M (2017). Maternal Race-Ethnicity, Immigrant Status, Country of Birth, and the Odds of a Child With Autism. Child neurology open, 4 PMID: 28503625