For the first time, researchers in the UK have shown that early parent-focused autism intervention has long-term benefits.

Early intervention aimed at helping parents communicate with their autistic child has a long-term effect on reducing the severity of symptoms, a study has found.

The study published in medical journal The Lancet showed the significant benefit continued for six years after the end of treatment.

Led by the University of Manchester, King's College London and Newcastle University in the UK, the researchers found that children who had received parent-focused intervention between the ages of two to four showed improved social communication and reduced repetitive behaviours.

No changes, however, were seen in other areas such as language or anxiety.

The researchers note that such intervention is no 'cure' and additional ongoing support will usually be needed as the children get older.

"This type of early intervention is distinctive in being designed to work with parents to help improve parent child-communication at home," says Professor Jonathan Green, who led the study.

Autism spectrum disorder is a lifelong neurological developmental condition that affects, among other things, the way an individual relates to his or her environment and their interaction with other people.

It affects about 1 in 100 people - that equates to about 230,000 Australians, mostly boys.

Symptoms vary in severity, with the main areas of difficulty in social communication, social interaction and restricted or repetitive behaviours and interests.

In the Preschool Austism Communication Trial, 152 children aged 2-4 with autism were randomly assigned to receive 12 months of early intervention or treatment as usual.

Follow-up analysis using the international standard measure of autism symptoms ADOS CSS - which combines social communication and restricted and repetitive behaviour symptoms into an overall measure of severity scored 1-10 - was conducted six years after the end of treatment.

Children in the intervention group scored an average 7.3 on the scale and 46 per cent were in the severe range.

By comparison, the children in the treatment as usual group scored on average 7.8 , with 63 per cent in the severe range.

This represents a reduction of 17 per cent in the proportion of children with severe symptoms in the intervention group.

Autism Spectrum Australia (ASPECT) has long supported early intervention, but Prof Green says the encouraging findings are the first to identify a long-term effect.

He says the advantage of the parent-focused intervention over a direct therapist-child intervention approach is that it has the potential to affect the everyday life of the child.

"The represent an improvement in the core symptoms of autism previously thought very resistant to change."