Earlier, it was suspected that autism runs in families, but the new study has declared that the risks are even higher than feared.

To reach to this conclusion, researchers studied 664 toddlers who had at least one elder brother or sister with autism. After following them, it was found that 19% or 132 infants among them were diagnosed with autism by the time they get to the age of three. Thereby, one in five children with an autistic older sibling will develop the disorder too.

Lead author Sally Ozonoff, a Psychiatry and Behavioral Sciences Professor with the Mind Institute at the University of California at Davis said they have referred to previous studies where the autism rise was by 3 to 14%, but this much high has shocked them.

The findings that got published online on Monday in Pediatrics have involved 12 U. S. and Canadian sites.

The belief that autism is more commonly associated with boys remains true. As only 9% of the girls and 26% of boys developed autism. And, major risk was to infants who had at least two older siblings with autism as 32% of them get diagnosed with autism.

Ozonoff said there is no particular reason of being diagnosed with autism, but genetics and external influences could be a reason.