Autism Spectrum Disorder, or ASD, affects almost 1 percent of all children born in the united states, but the individual risk and to what extent this is caused by genetic or environmental factors is uncertain. Now a new Swedish study finds the risk of autism may be influenced equally by genetic and environmental factors and the sibling of a family member with autism has a much higher risk for the disorder.

"So, one thing that this study tells us is that if you have a child with autism other children in the family are at 10 times greater risk, approximately to have autism," said Dr. Tom Frazier, who did not take part in this study but researches and studies autism at Cleveland Clinic Children's.

Researchers at the Karolinska Institute in Stockholm studied more than 2-million Swedish born children. Nearly 15,000 of them were diagnosed with Autism Spectrum Disorder, which is defined as impairment in social interaction and communication and the presence of restricted interests and repetitive behaviors. Nearly 5,700 children were diagnosed with autistic disorder, or autism, which is the most profound form of ASD.

Results show siblings are 10-times more likely to have ASD if they have a member of their immediate family with ASD. Cousins have 2-times the risk. The pattern was similar for autistic disorder. Researchers say based on their findings, about 50% of all autism diagnoses can be explained by genetics.  Frazier says the findings stress the importance of knowing your family history.

"It's another example of a study that tells us, in this case autism, but in many other psychiatric disorders you need to know the family history," said Frazier. "The family history can be important for you. It can help you to understand your risk. It doesn't necessarily mean it will change your behavior but it's always important to take into account your risks." 

You can read  more about this study in theJournal of the American Medical Association.