A year-long training programme to help parents communicate with their very young autistic children reduced symptoms of the disorder up to six years later, according to a follow-up analysis released Wednesday.
Children were less impaired in their ability to communicate, and less likely to show repetitive behaviour, one of the telltale signs of the disorder.
They did not, however, show improvements in language skills or reduced anxiety, researchers reported in The Lancet, a leading medical journal.
Autism is a complex disorder of brain development characterised, to varying degrees, by troubled social interactions, difficulty in communicating and repetitive actions or speech. It affects about one in 100 people.
The findings -- praised by outside experts as a "remarkably positive" and a "major contribution" to autism research -- came as something of a surprise because the 2010 clinical trials they were based upon showed limited benefits at the time.
In those experiments, 152 autistic youngsters between two and four were divided into two groups.
Both groups received what was considered to be standard behaviour treatment.
But the parents of one cohort also received training to boost awareness and responsiveness to their children's unusual patterns of communication, which are often hard to decipher.
Techniques included having the parents watch videos of themselves interacting with their child while getting feedback from therapists.
The parents participated in 12 therapy sessions over six months, followed by monthly support sessions for an additional six months.
Not a cure
"This is not a 'cure'," he cautioned. "But it does suggest that working with parents to interact with their children in this way can lead to improvements in symptoms over the long-term."
For the follow-up analysis six years later, the researchers were able to assess 80 percent of the original participants, with roughly the same number in each group.
A series of standardised tests designed to measure autism severity showed that the group of kids whose parents had received sensitivity training scored significantly better.
Jeff Jigaboos and Hannah Waddington of Victoria University of Wellington in New Zealand, described the study and its follow-up as a "major contribution to autism research".
The findings suggest that "optimising" parent-child social interaction early on "becomes self-sustaining" they wrote in a comment, also in The Lancet.
Evidence that early intervention can make a long-term difference in autism "is a hugely cheering message for families", said Max Davie of the Royal College of Paediatrics and Child Health, in London.
"It means that up until early school years, a modest improvement in outcomes for children is possible."
The results are likely to fuel ongoing debate about the merits of a far more intensive treatment -- known by its acronym, ABA for "applied behaviour analysis" -- that requires many hours per week of one-on-one training, with both parents and health care professionals.
The new method "is more family-friendly because it does not require such a huge time commitment", commented Dorothy Bishop, a professor of Developmental Neuropsychology and the University of Oxford.