A new study published this week in the journal Nature shows that children as young as six months old may show signs of autism.

Researchers observed that for infants between the age of two and six months a decline in eye contact is associated with a later autism diagnosis. This is compared to most infants, who tend to focus on faces and eyes. A lack of eye contact is an autism symptom for even people who are not infants.

The study’s authors followed children from birth until 3 years old, using eye-tracking devices to capture eye movements while videos played on a screen. Some of the infants were classified as “high risk” for autism, as they had a sibling that was already diagnosed with the disorder. All of the children were tested ten times between 2 months and 2 years of age.

After a third year the researchers looked back to see if patterns emerged for those children who had since been diagnosed with autism. They found that children later diagnosed with autism saw a steady decline in eye contact that began at just two months and continued until the end of the study. By age two, the study participants with autism were focusing on the eyes of the woman in the video only half as much as other children.

“Autism isn’t usually diagnosed until after age 2, when delays in a child’s social behavior and language skills become apparent,” said Dr. Thomas Insel, director of the National Institute of Mental Health. “This study shows that children exhibit clear signs of autism at a much younger age. The sooner we are able to identify early markers for autism, the more effective our treatment interventions can be.”