Children with autism can be identified as early as 14 months old, the youngest age at which the disorder has been diagnosed, a study by researchers at the Kennedy Krieger Institute in Baltimore suggests.

But about half the time, symptoms may not show up until months later. That suggests at least two distinct paths leading to autism: one that starts early in life and one in which a child seems to develop normally and then regresses, losing language and social skills.

Results of the study, the first to follow toddlers from 14 months until they turn 3, could allow earlier treatment to reduce the effects of autism, says Rebecca Landa, lead author of the report published in the Archives of General Psychiatry.

The range of developmental impairments known as autism spectrum disorders, or ASD, is marked by an inability to communicate and interact with others. Its cause is not known, but most researchers believe genetic factors play a role.

Most studies have relied on interviews with parents and examinations of family videos to look for early signals, such as a child's lack of response to his name or failure to engage with others.

Scientists know that "we can reliably diagnose autism at age 2, but only by real experts," Landa says. "What's different about this is we can show that we can stretch that down close to the first birthday, but the caveat is we can't do it for all children."

The study involved 107 children who were considered at high risk for autism because they had a sibling with the disorder and 18 low-risk children who had no family history of autism.

Behavior differences in those with and without ASD at 14 months can be seen in videos that show toddlers interacting with a researcher. In one, a normally developing boy reacts happily when given a toy penguin, gives it to the researcher and laughs when she hands it back. "He integrates looking, giving and smiling," Landa says. "That is what I call the package, and the package is very seldom seen at 14 months of age in kids who have ASD."

By contrast, a boy later diagnosed with autism shows only mild interest when a researcher uses a blanket to play peek-a-boo. He focuses briefly on the blanket, but he doesn't interact with the researcher and soon loses interest.

Children in the "late-diagnosis group" behave at 14 months old very much like the children who didn't end up with autism, Landa says. But from 14 to 24 months of age, there was a progressive decline in social development. "Whatever is happening, it's affecting brain development in a way we can observe behaviorally," she says. "We can't watch the neurons making connections, but we can watch a child's smile disappear."

Landa cautions parents not to be overly alarmed if a child occasionally exhibits a worrisome trait. Autism involves many developmental disruptions that continue over time. "I don't know any children who don't do weird things" now and then, she says. "If it's going to be ASD, it's going to stick."

BEHAVIORS TO LOOK FOR

No single behavior is enough to diagnose autism, researchers say, but here are some signs to watch for at age 14 months: