LOS ANGELES — Children with autism spectrum disorders usually aren't diagnosed until they are at least 2 years old, but a new study finds that signs of the condition are apparent as early as two months after birth.

Researchers focused on babies' ability to make eye contact with caregivers, since lack of eye contact is one of the hallmarks of autism. Among typical children, interest in the eyes increased steadily with age. But for children with autism, interest in the eyes waned starting between 2 and 6 months of age.

By the time they reached their second birthdays, levels of eye fixation among children with autism were only half as high as levels seen in typically developing children, according to a report published Wednesday by the journal Nature.

Although researchers expected to see a difference between the two groups of kids, they were surprised that the infants who were later diagnosed with autism started out developing just like their peers. That suggests that "some social adaptive behaviors may initially be intact" in babies' brains, which would "offer a remarkable opportunity for treatment," the researchers wrote.

Warren Jones and Ami Klin of the Marcus Autism Center at Emory University School of Medicine in Atlanta recruited 110 infants for their study. Among them, 59 had a full sibling with an autism spectrum disorder and thus were considered at high risk of developing the condition themselves. An additional 51 infants who had no first-, second- or third-degree relatives with autism were considered low-risk, and they served as controls.

The infants were shown "scenes of naturalistic caregiver interaction" while the researchers used eye-tracking technology to monitor where the babies focused their gazes. They measured the proportion of time spent paying attention to the woman's eyes, mouth, body (including neck, shoulders and hair) and nearby inanimate objects.