A large international study of the genes that predispose people to autism spectrum disorders (ASD) suggests that the same gene variants are also present in the wider population, where they can contribute to a range of behavioural and developmental traits with lesser severity than clinical ASD.

According to the researchers, there's no real cut-off point on the autism spectrum – rather, it's a continuum of complex genetic factors that can affect our behaviour. But for a small percentage of the community who have more of certain gene variants than others, this gives them a greater likelihood of demonstrating the social and behavioural traits recognised as clinical ASD.

"This is the first study that specifically shows that [genetic] factors that we have unambiguously associated with autism are also very clearly associated with social communication differences in the general population," geneticist Elise Robinson from Harvard University told Nicola Davis at The Guardian.

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How do the scientists know this? By comparing data on some 38,000 individuals sourced from a number of studies on cohorts of both ASD-affected and unaffected individuals. By studying polygenic risk factors (small effects of thousands of genetic differences, distributed across the genome) and de novo risk factors (rare genetic variants of large effect), in these data sets, the continuum of ASD-related traits became clear.

"There has been a lot of strong but indirect evidence that has suggested these findings," said researcher Mark Daly, co-director of the Broad Institute's Medical and Population Genetics (MPG) program. "Once we had measurable genetic signals in hand – both polygenic risk and specific de novo mutations known to contribute to ASD – we were able to make an incontrovertible case that the genetic risk contributing to autism is genetic risk that exists in all of us, and influences our behaviour and social communication."

However, just because everybody carries some degree of genetic risk when it comes to ASD gene variants, doesn't mean we all would find social interactions difficult to some extent, nor that people's genetic makeup is the only reason they might develop ASD.

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"We can use behavioural and cognitive data in the general population to untangle the mechanisms through which different types of genetic risk are operating, " said Robinson. "We now have a better path forward in terms of expecting what types of disorders and traits are going to be associated with certain types of genetic risk."

Autismus ist genetisch bedingt. Das legten ersten Studien bereits Ende der 1970er-Jahre nahe. Die heutige molekulare Humangenetik bestätigt diese frühen Schlussfolgerungen. Der Genetik-Experte Prof. Dr. Rolf Knippers [Jahrgang 1936] wirft in seinem Buch „Autismus, genetisch betrachtet“ (Georg Thieme Verlag, Stuttgart. 2016) einen umfassenden Blick auf die Forschungsgeschichte zur molekularen Genetik des Autismus.

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Die moderne genetische Forschung versucht, spezifische Gene oder Gengruppen einzelnen Symptomen des Autismus-Spektrums zuzuordnen. 2003 gab es erste Antworten auf die Frage, welche Gene bei Autismus verändert seien. „Es stellte sich heraus, dass viele Gene beteiligt sind und die Genetik des Autismus alles andere als einfach, sondern im Gegenteil sehr komplex ist“, erklärt Knippers. „Heute geht man davon aus, dass es Hunderte von Risikogenen gibt, die an mehreren Stellen bei der Entwicklung der neuronalen Netzwerke im Gehirn wirksam sind.“ Laut dem Autismus-Experten wird es zukünftig darum gehen, die Funktion einzelner Gene im Detail zu klären und mit diesem Wissen die neuronalen Schaltkreise und Netzwerke zu identifizieren, die bei Autismus verändert und beschädigt sind.
„Dieses Wissen wird die psychologische und psychiatrische Praxis bereichern, und zwar durch verbesserte diagnostische Möglichkeiten und vielleicht auch durch plausible Forschungsprogramme zur Entwicklung neuer Medikamente führen“, so Prof. Knippers.