Genetic influences on autism estimated at between 74-98 per cent

Researchers have found that Autism Spectrum Disorder (ASD) is more heritable than recent studies have suggested with genetic influences on the disorder estimated to fall between 74-98 per cent.

Genetic risk factors for ASD were also found to overlap with the genes that influence less extreme autistic skills and behaviours seen in the general population.

The study was carried out by researchers at the Institute of Psychiatry, Psychology & Neuroscience (IoPPN), King's College London and published today in JAMA Psychiatry.

''Our main finding was that the heritability of ASD was high. These results further demonstrate the importance of genetic effects on ASD, despite the dramatic increase in prevalence of the disorder over the last 20 years,'' said lead author Beata Tick from the IoPPN, King's College London.

''They also confirm that genetic factors lead to a variety of autistic skills and behaviours across the general population.'' 

Data came from the population-based Twins Early Development Study (TEDS), funded by the UK Medical Research Council (MRC), and included all twins from the TEDS born in England and Wales between 1994 and 1996. In depth, home-based evaluations were carried out on 258 twins selected from the initial group of over 6,000 twin pairs, using state-of-the-art diagnostic interviews and play-based assessments, and 181 twins from the subgroup were diagnosed with ASD. 

Results were consistent across several diagnostic tools and the robust findings could be used as a benchmark for future work in the field. 

Professor Patrick Bolton, a senior author also from the IoPPN at King's, said, ''The comparison of identical and non-identical twins is a well-established way of clarifying the extent of genetic and environmental influences in autism.

''The novel aspect of this study was the inclusion of twins regardless of whether they had a clinical diagnosis. This enabled us to get a more accurate picture of how influential a child's environmental experiences and their genetic makeup is on ASD, as well as on subtler expressions of autistic skills and behaviours. 

''Our findings add weight to the view that ASD represents the extreme manifestation of autistic skills and behaviours seen in the general population.''

Funding for the Twins Early Development Study was by the UK MRC, and the Social Relationship Study was also funded by the MRC. Further support for the study was from the National Institute for Health Research Maudsley Biomedical Research Centre at King's and the South London and Maudsley NHS Foundation Trust, and an Autism Speaks grant