The Analyze Blog

Corpus Callosum Development in Autism is Different for Girls

By AnalyzeDirect Staff, last updated March 17, 2016

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AutismAutism is a global problem with skyrocketing incidence rates. The CDC reports that 1 in 68 children born today will be diagnosed with autism spectrum disorder (ASD). The incidence for boys is 1 in 42, so the majority of research studies has focused on males. This has led to a poorly understood and little-studied population of girls with ASD, who have an incidence rate of 1 in 189.

The literature has shown that anomalies in the development of the corpus callosum, a fiber bundle in the brain responsible for neocortical connectivity, might have a role in the progression of autism spectrum disorder.

While many studies have evaluated callosal deficits in children, adolescents and adults with ASD, very few have assessed sex differences in preschool-aged children. In order to gain more information regarding gender-specific brain differences, researchers from the University of California at Davis recently investigated the development of the corpus callosum in 139 children from 3 to 5 years of age, 112 male and 27 females.

Through the evaluation of structural and diffusion-weighted images, the team was able to determine the size of the corpus callosum and the organization and diffusion characteristics of callosal fibers. From T1-weighted images, Analyze software was used to manually delineate the midsagittal area of the corpus callosum and to segment it into its seven subdivisions: rostrum, genu, rostral body, anterior midbody, posterior midbody, isthmus, and splenium.

When compared to typically developing controls, both females and males with ASD showed decreased midsagittal area but no differences in subdivisions. Males with ASD exhibited a smaller region of fibers connecting the orbitofrontal cortex and a larger region associated with the anterior frontal cortex, compared to females with the same neurodevelopmental disorder. When it came to diffusion measures, the team observed a more significant alteration in mean diffusivity, axial diffusivity, and radial diffusivity in females with ASD than in males.

This study provides valuable knowledge on how callosal organization differs in males and females. In fact, sex differences in the pattern of callosal alterations in autism spectrum disorder may be responsible for the ‘female protective effect’ that makes this condition more difficult to detect in females. Future studies by this research group will include targeted recruitment of girls with autism, to study brain differences in boys and girls with ASD, as well as to their typically developing peers.

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