Girls and boys diagnosed with autism display different behaviours and this can be explained by a difference in their brain structure, say scientists, inlcuding those of Indian-origin.
Researchers at the Stanford University School of Medicine found that girls with autism display less repetitive and restricted behaviour than boys do.
They also found that brain differences between boys and girls with autism help explain this discrepancy.
The study gives the best evidence to date that boys and girls exhibit the developmental disorder differently, researchers said.
"We wanted to know which specific clinical manifestations of autism show significant gender differences, and whether patterns in the brain's gray matter could explain behavioural differences," said the study's senior author, Vinod Menon, professor of psychiatry and behavioural sciences.
"We found strong evidence for gender differences in autism," said lead author Kaustubh Supekar, a postdoctoral scholar at Stanford University.
The researchers used two large, public databases to examine nearly 800 children with high-functioning forms of autism in the US.
Repetitive and restricted behaviour is perhaps the most widely recognised of the three core features of autism.
It can show up as a child's preoccupation with a narrow interest, inflexibility about routines or repetitive motions such as hand-flapping. The other core features of autism are social and communication deficits.
Scientists were interested in comparing the expression of core features of the disorder between sexes because they have long suspected girls with autism may display symptoms differently, causing them to be underdiagnosed.
The study examined the severity of autism symptoms in 128 girls and 614 boys. The children ranged in age from 7 to 13, had IQ scores above 70, and had been evaluated with standard tests for autistic behaviour.
The boys and girls were matched for age, and had the same average IQ. Girls and boys had similar scores for social behaviour and communication.
But girls had lower (more normal) scores on a standard measurement of repetitive and restricted behaviours.
The researchers then examined data from the Autism Brain Imaging Data Exchange that included structural MRI brain scans of 25 boys with autism, 25 girls with autism, 19 typically developing boys and 19 typically developing girls.
The researchers again found that girls and boys did not differ on social behaviour and communication skills, but that girls had less-severe repetitive and restricted behaviours.
The brain-scan analysis showed several gender differences in brain structure between typically developing boys and girls.
Children with autism, however, had a dissimilar set of gender differences in the brain regions that affect motor function and planning of motor activity.
The study was published in the journal Molecular Autism.
