There was a CDC report recently that defined "profound autism" as "nonverbal, were minimally verbal, or had an intelligence quotient <50". They found roughly 2

There was a CDC report recently that defined "profound autism" as "nonverbal, were minimally verbal, or had an intelligence quotient <50". They found roughly 25% of kids diagnosed by age 8 fitted this category. This category seems to be growing, but not as fast as autism disgnosis generally. The obvious statistical issue here is that to have received a diagnosis by age 8 you need to be showing more severe symptoms. This shows up in the fact that these kids are "more likely to be female, from racial and ethnic minority groups, of low socioeconomic status" compared with kids with autism generally because the ability to get diagnosed for milder forms is harder for those groups (more mildly autistic girls seem to mask their social symptoms better than boys, which has historically led to them being undercounted and unrepresented in the common stereotype). https://journals.sagepub.com/doi/10.1177/00333549231163551 https://journals.sagepub.com/doi/10.1177/00333549231163551