The genes associated with autism "are in all of us", including those who have not been diagnosed with a condition on the spectrum, new research suggests.
Researchers from the University of Bristol, the Broad Institute of Harvard and MIT, and Massachusetts General Hospital investigated the genetic relationship between autistic spectrum disorders (ASD) and ASD-related traits in people not considered to have ASD.
They found that genetic risk for ASD exists in all people, but we display symptoms associated with the condition to "various degrees".
According to the study authors, autism spectrum disorders (ASD) are a class of neurodevelopmental conditions affecting about one in 100 children.
The disorders are characterised by social interaction difficulties and communication and language impairments, as well as stereotyped and repetitive behaviour.
These core symptoms are central to the definition of an ASD diagnosis but also occur, "to varying degrees", in unaffected individuals and form an "underlying behavioural continuum".
The researchers noted that most ASD risk is polygenic, meaning it stems from the combined small effects of thousands of genetic differences, distributed across the genome (a set of genes present in a cell).
But in some cases, ASD risk is also linked to rare genetic variants or mutations, which are usually de novo (not inherited).
"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," senior study author Dr Mark Daly said.
Study co-author Dr Elise Robinson added: "We can use behavioural and cognitive data in the general population to untangle the mechanisms through which different types of genetic risk are operating. 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."
The researchers now plan to explore the associations between genetic risk and behavioural traits in other neuropsychiatric disorders such as schizophrenia.