Neuroimaging study maps differences in the brains of girls and boys with autism.


New research conducted by the UC Davis MIND Institute on a large cohort of preschoolers with autism spectrum disorder has found differences in the underlying biology of their brains, and in their behaviour, that may help explain how the condition affects a little-studied and poorly understood population of children, girls.

The team state that Autism Spectrum Disorder is diagnosed much more frequently in boys than girls, at a ratio of 4 to 1. Despite recent efforts, little research has been done on girls as there are fewer of them, so fewer are represented in autism research. An estimated 1 in 42 boys has autism; in girls the statistic is 1 in 189.  The U.S. Centers for Disease Control and Prevention currently estimates the overall incidence of autism at 1 in 68 children born today.

In a neuroimaging study, the researchers found differences in the corpus callosum, the region of the brain that connects the left and right hemispheres.  The opensource study is published in the journal Molecular Autism, as part of a special issue devoted to gender differences. It adds to the growing body of evidence that suggests that, in autism, there are underlying tangible biological differences between boys and girls.

In previous studies the researchers found that the behavioural differences between girls who have autism and typically developing same-age girls are much greater than the differences between boys with autism and typically developing same-age males. The finding suggests that girls with autism have greater social impairments than do boys.  The research was part of the Girls with Autism Imaging of Neurodevelopment (GAIN) study.

The team state that previous studies have made it clear that it’s important to identify differences in underlying biology in boys and girls, because this could help researchers determine whether there are different etiologies of autism, and that potentially could lead to different treatments and interventions.

The current magnetic resonance imaging (MRI) study of brain structure was conducted in a large sample of 3- to 5-year-old children, 112 boys and 27 girls, a large number for girls with autism, and 53 boys and 29 girls who were developing typically and served as control subjects.  Previous studies have found alternations in the corpus callosum in children and adults with autism, but most were focused on males only, or had very small female sample sizes, stress the team.

The current study used a technique called diffusion tensor imaging (DTI), a type of magnetic resonance imaging that allowed the researchers to neuroanatomically subdivide the corpus callosum, based on where in the cerebral cortex the fibers projected.

The data findings showed that the organization of callosal fibers was different in boys and girls with autism, particularly those projecting into the frontal lobes.  The frontal lobes are involved in many aspects of functioning, including social behaviour, goal-directed behaviour and executive functioning. The team hypothesize that differences in the patterns of callosal fibers projecting to these areas may lead to differences in how autism manifests in boys and girls.

In a previous study on sex differences in social impairment in preschool-aged children with autism spectrum disorder the researchers explored behavioural differences in boys and girls with autism. The team note that past research in the area has been inconsistent.

The team state that most behavioural studies of gender differences directly compare males and females with autism. Their approach was to evaluate social impairments in a large group of children that included girls and boys with both autism and typical development.   The researchers say they were interested not only in directly comparing boys and girls with autism, but also in assessing how boys and girls with autism compare in relation to their typically developing peers.

The previous studies found that the behavioural differences between girls with autism and typically developing girls are much larger than differences between boys with autism and typically developing boys.  The results showed that girls with autism deviate further from typically developing girls than boys with autism relative to typically developing males, suggesting that girls with autism have more severe social impairments than boys.

The team surmise that much more works needs to be done to understand the sex differences between male and female children with autism, and particularly, increasing the numbers of female children who participate in autism research.

Future studies from the laboratory will include targeted recruitment of girls with autism, in order to carry out a comprehensive evaluation of behavioural and neurobiological differences in boys and girls with autism in relation to each other, as well as to their typically developing peers.

There definitely is a need to evaluate more girls with autism, to fully understand the differences between boys and girls, the team conclude, adding that the GAIN Study hopes to evaluate an additional 100 preschool-aged girls with autism during the next three years.

Source:  UC Davis Health System

 

Sex differences in cortical projection zone subregions across three MRI time points. Estimated trajectories depicted were estimated for TCV equal to the time 1 average for TD children before the scanner upgrade. (A) The orbitofrontal fiber region is smaller in males with ASD than in TD males but does not differ in females. (B) The anterior frontal fiber region is smaller in females with ASD than in TD females. In males, the opposite pattern is observed; males with ASD are larger than TD males. (C) The superior frontal fiber region is smaller in both males and females with ASD than TD counterparts, though the difference is larger in females.  Sex differences in the corpus callosum in preschool-aged children with autism spectrum disorder.  Nordahl et al 2015.

Sex differences in cortical projection zone subregions across three MRI time points. Estimated trajectories depicted were estimated for TCV equal to the time 1 average for TD children before the scanner upgrade. (A) The orbitofrontal fiber region is smaller in males with ASD than in TD males but does not differ in females. (B) The anterior frontal fiber region is smaller in females with ASD than in TD females. In males, the opposite pattern is observed; males with ASD are larger than TD males. (C) The superior frontal fiber region is smaller in both males and females with ASD than TD counterparts, though the difference is larger in females. Sex differences in the corpus callosum in preschool-aged children with autism spectrum disorder. Nordahl et al 2015.

 

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