Although the results from our comparison of recurrence in full- and half-siblings support the role of genetics in ASDs, the significant recurrence in maternal half-siblings may support the idea of a contributing role of factors associated with pregnancy and the maternal intrauterine environment. Finally, the lack of a time trend in the relative recurrence risk in our data suggests that the likely combination of genetic and environmental factors contributes to the risk for ASD recurrence in siblings or that the risk for recurrence because of such factors has not been affected by the rise in the ASD prevalence. The current Denmark study included individuals diagnosed until the end of 2010. I.e. there were 10 more years of followup. In those 10 years a lot more people were diagnosed. Where there were 956 diagnosed with autism by 2000 (for birth years 1971 to 2000), 2321 were diagnosed by 2010. That’s an increase of 240%. And the new study focused on birth years 1980 to 1999. I.e. the entire 1970′s birth cohort is not included in this count, and they still found over twice as many autistics. Where were they in 2000, when the previous study was performed? Living in Denmark, not identified as autistic. And, those numbers were for childhood autism. For ASD, the increase is even larger. 10,377 Danes had an autism spectrum disorder diagnosis (for birth years 1980-1999) in the new study (the previous study included none). That’s a whopping 1080% increase. Again, there are a few reasons for this (including the increased awareness above), but here’s what “expanding the definition” does to autism. Those increases would be an “epidemic” to some if it weren’t for the fact that those autistic Danes were there all along. They just weren’t diagnosed in 2000.
Read more here.