Rate of severe autism rising at slower pace than milder forms, study finds

A quarter of American children identified as autistic by age 8 have the most severe form of the disorder, a new study found.
The rate of severe autism diagnoses grew from about 3 cases per 1,000 children in 2000 to 5 cases per 1,000 in 2016, according to the study.
In contrast, the prevalence of milder autism has been rising much more rapidly.
There are wide racial gaps in the rates of severe autism, with black children having the highest rates.
The study provides the first solid numbers on the share of U.S. children with the most profound autism and suggests the need to differentiate between mild and severe cases..