What causes autism is one of the greatest medical mysteries, but a new study may shed light on some risk factors.

Researchers studied the birth demographics of a group of eight year-old children in Utah. They found children who developed an Autism Spectrum Disorder were more likely to be born the first born to mothers over the age of 35 years-old and have been in the breech position at birth.

About 1 in 150 children is diagnosed with autism and it's four times more likely to strike in boys than girls.