Scientists studied 34 school-age children and young adults who had been diagnosed with autism early in life but now appeared to be functioning normally.
Tests confirmed that the group, aged eight to 21, no longer suffered symptoms of the developmental condition that makes it difficult to communicate and socialise.
Researchers led by Deborah Fein, from the University of Connecticut, matched the 34 children by age, sex, and nonverbal IQ with 44 kids with high-functioning autism, and 34 typically developing peers. Participants ranged in age from 8 to 21 years old.
Prior studies had examined the possibility of a loss of diagnosis, but questions remained regarding the accuracy of the initial diagnosis, and whether children who ultimately appeared similar to their mainstream peers initially had a relatively mild form of autism.
The results suggested that children in the optimal outcome group had milder social deficits than the high functioning autism group in early childhood, but had other symptoms, related to communication and repetitive behaviour, that were as severe as in the latter group.
The investigators evaluated the current status of the children using standard cognitive and observational tests and parent questionnaires.
"All children with ASD are capable of making progress with intensive therapy, but with our current state of knowledge most do not achieve the kind of optimal outcome that we are studying," said Fein.
"Our hope is that further research will help us better understand the mechanisms of change so that each child can have the best possible life," Fein said in a statement.
This study cannot provide information on what percentage of children diagnosed with ASD might eventually lose the symptoms.
Analysis of those data may shed light on questions such as whether the changes in diagnosis resulted from a normalising of brain function, or if these children's brains were able to compensate for autism-related difficulties.