Washington: Researchers have said that environmental factors are more important than previously believed in understanding the causes of autism and equally as important as genes. The study also 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. The study led by researchers at King's College London Karolinska Institutet in Sweden and Mount Sinai in the US looked at over 2 million