Socioeconomic gradients in autism cases may not be self-selected

Throughout my life, I've often been told (usually by way of consolation) that autistic children are born to intelligent families. One of my two younger brothers has severe autism. I was very young when he was diagnosed, and for a while he was treated as though he had a speech and language disorder. If I had to guess, I would say that he was diagnosed around the age of 5-6. The earliest warning sign was that he didn't start talking at the stage in development where that usually happens. While my brother is still fond of social interaction, his main symptom to this day (he's now 23) remains an inability to carry a conversation. He uses language in a very crude manner, only stringing together 2-3 words at a time. "Go potty." "All done." "Hungry." I have lots of feelings on this subject (believe me), but that's not the point of this post.

The dogma that autism is a disease of high(er) intelligence and socioeconomic status has been around since the first diagnoses for autism came out when my grandparents were kids. This is in opposition to the norm, where the prevalence of developmental disabilities is most often inversely related to socioeconomic status because parents in poor communities have fewer resources for parenting education and health services. In recent years, the argument that the higher prevalence of autism cases in families of higher socioeconomic status is self-selected; that is, parents with more access to resources and information about autism are more likely to seek out proper diagnosis and treatment for their child(ren).

In Socioeconomic Inequality in the Prevalence of Autism Spectrum Disorder: Evidence from a U.S. Cross-Sectional Study, Durken and colleagues studied datasets for several states from the Autism and Developmental Disabilities Monitoring Network to see if there was a change in the prevalence of autism rates due to socioeconomic gradient between cases where the child had a prior diagnosis for an autism spectrum disorder and cases where there was no prior diagnosis.

We designed the present study to examine—among a large, diverse, population-based sample of 8-year-old children in the United States in which ASD case status was determined regardless of whether a child had a pre-existing ASD diagnosis—whether the prevalence of ASD is associated with SES and, if so, whether the association is consistent across subgroups defined by race/ethnicity, gender, phenotypic characteristics, diagnosis, and data sources.

The authors found strong evidence of a positively-correlated socioeconomic gradient in children with autism spectrum disorders. This gradient was weaker but remained a positive relationship in children without a prior diagnosis. This means that even in cases where the parents did not seek diagnosis for their child, there was still an increase in autism cases with increasing socioeconomic status, albeit a weaker one. This is evidence that, while the magnitude of the gradient may be self-selected, there is very likely still a positive relationship between socioeconomic status and prevalence of autism. The causes for this relationship remain to be explored, but one possibility could be the average reproductive age of highly educated females vs. less educated females and other hidden factors.

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Durkin, M., Maenner, M., Meaney, F., Levy, S., DiGuiseppi, C., Nicholas, J., Kirby, R., Pinto-Martin, J., & Schieve, L. (2010). Socioeconomic Inequality in the Prevalence of Autism Spectrum Disorder: Evidence from a U.S. Cross-Sectional Study PLoS ONE, 5 (7) DOI: 10.1371/journal.pone.0011551