I just saw this post on Facebook:
Detecting Autism From Brain Activity
Roberto Fernández Galán, PhD, an assistant professor of neurosciences at Case Western Reserve and an electrophysiologist seasoned in theoretical physics led the research team that detected autism spectrum disorder (ASD) with 94 percent accuracy. The new analytic method offers an efficient, quantitative way of confirming a clinical diagnosis of autism.
Previously, there has not been a definitive way to diagnose it, as far as I know.