WEDNESDAY, June 29 (HealthDay News) -- Variations of a certain gene affect the amount of time people spend looking at happy faces, a finding that may help improve understanding of social behavior and autism, according to researchers.

Looking at people's faces helps us read their emotions, but some people are reluctant to gaze at others' faces. This is especially true of people with autism.

The researchers analyzed DNA from 28 adult volunteers and tested how long they looked at video clips of eyes and mouths of faces with different emotions. They found that people with two types of variations in the cannabinoid receptor (CNR1) gene spent more time gazing at happy faces, but not at faces showing disgust.

The study is published online June 28 in the journal Molecular Autism.

"This is the first study to have shown that how much we gaze at faces is influenced by our genetic make-up. If replicated it has profound implications for our understanding of the drive to socialize, and in turn, the atypical use of gaze in autism," study co-leader Bhismadev Chakrabarti, of the University of Reading in England, said in a journal news release.

More information

The U.S. National Institute of Neurological Disorders and Stroke has more about autism.