Environment as important as genes in understanding autism
Environmental factors are more important than previously thought in understanding the causes of autism, and equally as important as genes, according to the largest study to date to look at how autism runs in families. The findings are published in the scientific periodical JAMA.
Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder defined by impairments in social interaction and communication and the presence of restrictive and repetitive behaviours. The exact causes are unknown but evidence has shown it is likely to include a range of genetic and environmental risk factors.
The current study, which was conducted by researchers at Karolinska Institutet, King’s College London in the UK, and Mount Sinai in the US, shows that children with a brother or sister with autism are 10 times more likely to develop autism; 3 times if they have a half-brother or sister; and 2 if they have a cousin with autism, providing much needed information for parents and clinicians for assessing individual risk. Using Swedish national health registers, the researchers analysed anonymous data from all 2 million children born in Sweden in between 1982 and 2006, of which 14,516 had a diagnosis of ASD. The researchers analysed pairs of family members: identical and non-identical twins, siblings, maternal and paternal half-siblings and cousins.
Most previous studies have suggested that heritability of autism – which is the proportion of risk in the population that can be attributed to genetic factors – may be as high as 80-90%. The new study is the largest and most comprehensive to date and estimates heritability of autism to be 50%, with the other 50% explained by non-heritable or environmental factors.
The study was funded by the Swedish Research Council, the US National Institutes of Health and the Beatrice and Samuel A. Seaver Foundation, New York.
Sven Sandin, Paul Lichtenstein, Ralf Kuja-Halkola, Henrik Larsson, Christina M. Hultman, Abraham Reichenberg
JAMA, online 3 May 2014, doi:10.1001/jama.2014.4144, 2014;311(17):1770-1777