As a disorder, it's quite new, so it's quite natural that the increase of diagnoses increased in the past few decades.
Also, if I'm not mistaken, the research behind genetics of brain issues is quite straightforward. It's thanks to twins - we analyse occurrence in monozygotic and dizygotic twins. If there is far higher correlation of the disease in monozygotic compared to dizygotic, we know it's genetic.
"Concordance in ASD diagnosis ... is observed in monozygotic (MZ) twin pairs at rates of 60-90%, whereas rates among dizygotic (DZ) twins are estimated at 3-31%."
http://www.parents.com/health/autism/history-of-autism/
As a disorder, it's quite new, so it's quite natural that the increase of diagnoses increased in the past few decades.
Also, if I'm not mistaken, the research behind genetics of brain issues is quite straightforward. It's thanks to twins - we analyse occurrence in monozygotic and dizygotic twins. If there is far higher correlation of the disease in monozygotic compared to dizygotic, we know it's genetic.
http://theautismblog.seattlechildrens.org/twins-autism/
"Concordance in ASD diagnosis ... is observed in monozygotic (MZ) twin pairs at rates of 60-90%, whereas rates among dizygotic (DZ) twins are estimated at 3-31%."