New York, Sep 4 (IANS): Girls with autism display less repetitive and restricted behaviour than boys -- and this could be the reason behind their being underdiagnosed or making it harder for them to get the most appropriate treatment, according to a new study.

The study -- conducted by a team at Stanford University's school of medicine which includes a number of Indian origin scientists -- also found that brain differences between boys and girls with autism help explain this discrepancy.

"Autism has primarily been studied from the viewpoint of boys with the disorder. Understanding gender differences can help in identifying the behavioural skills that are most important to remediate in girls vis-a-vis boys," said study's senior author professor Vinod Menon.

Among children diagnosed with the high-functioning form of autism, boys outnumbered girls by four to one.

The study examined the severity of autism symptoms in 128 girls and 614 boys registered with the National Database for Autism Research.

The children ranged in age from 7 to 13, had IQ scores above 70, and were evaluated with standard tests for autistic behaviour.

But girls had lower (more normal) scores on a standard measurement of repetitive and restricted behaviours.

Children with autism, however, had a dissimilar set of gender differences in their brains -- specifically, in the motor cortex.

These regions affect motor function and planning of motor activity.

"The discovery of gender differences in both behavioural and brain measures suggests that clinicians may want to focus diagnosis and treatments for autistic girls differently than boys," said lead author Kaustubh Supekar.

The findings were published online in the journal, Molecular Autism.