Autism is a lifelong neurodevelopmental disorder that affects how a person communicates with, and relates to, other people. Repetitive and restricted behaviour is perhaps the most widely recognized of the three core features of autism, a spectrum disorder. 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.
Boys are at higher risk for Autism than girls. Several theories about the higher prevalence in males have been investigated, however, the cause of the difference is unconfirmed; one theory is that females are underdiagnosed. Now, a study from researchers at Stanford University shows that girls with autism display less repetitive and restricted behaviour than boys do. The new study also found that brain differences between boys and girls with autism help explain this discrepancy. The team states that to their knowledge this data is the best evidence to date that boys and girls exhibit the developmental disorder differently. The opensource study was published in Molecular Autism.
Previous studies show that among children diagnosed with the high-functioning form of autism, boys outnumber girls. The sex ratio averages 4.3-to-1 and is greatly modified by cognitive impairment, it may be close to 2-to-1 with intellectual disability and more than 5.5-to-1 without. This may be why autism has primarily been studied from the viewpoint of boys with the disorder. It has been shown that understanding gender differences can help in identifying the behavioural skills that are most important to remediate in girls vis-a-vis boys. Therefore, in the current stuy, the lab 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 or making it harder for them to get the most appropriate treatment. The researchers state that they found strong evidence for gender differences in autism.
The current 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 had been evaluated with standard tests for autistic behavior. The boys and girls were matched for age, and had the same average IQ. Results showed that girls and boys had similar scores for social behaviour and communication. However, the group observed that girls had lower (more normal) scores on a standard measurement of repetitive and restricted behaviors.
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 individuals among the groups were matched for age and IQ. Results again showed that girls and boys did not differ on social behaviour & communication skills, and that the female participants had less-severe repetitive and restricted behaviours. The team state that this replication provides the strongest evidence to date for gender differences in a core phenotypic feature of autism.
Neuroimaging was then performed in the current study to identify which specific clinical manifestations of autism show significant gender differences, and whether patterns in the brain’s gray matter could explain behavioural differences. The lab explain that knowledge of the difference could help clinicians better recognize and treat autism in both sexes.
The brain-scan analysis revealed several gender differences in brain structure between typically developing normal boys and girls. Brain scans in the children with autism however had a dissimilar set of gender differences in their brains, specifically, in the motor cortex, supplementary motor area and a portion of the cerebellum. The team note that these regions affect motor function and planning of motor activity and that many repetitive behaviors, such as hand-flapping, have a motor component. The current study demonstrated that patterns of gray matter in these motor regions could accurately distinguish girls from boys with autism. The researchers conclude that parts of the motor system that contributed to individual scores for repetitive and restricted behaviors were different in boys and girls.
The researchers surmise that girls and boys with autism differ in their clinical and neurobiological characteristics, and their brains are patterned in ways that contribute differently to behavioural impairments. For the future, the group state that 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.