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Exciting Study Provides Insight to Heterogeneity in Autism

Author: Henry Blair


An exciting study, Brain mapping across 16 autism mouse models reveals a spectrum of functional connectivity subtypes, came out last year from Italy and Switzerland. The researchers offer key insights into the heterogeneity of autism spectrum disorder (ASD). Autism, like most neurodevelopmental and social learning disorders, does not have a definitive cause. Recent studies often dive into different neuroimaging techniques, such as magnetic resonance imaging (MRI), functional connectivity MRI (fcMRI), diffusion tensor imaging (DTI), single-photon emission computed tomography (SPECT),etc., but are unable to find a singular commonality between people with autism.


The most popular of these techniques is currently the fcMRI, which can highlight differences in neuronal signaling between controls and subjects with autism by measuring measuring blood flow and oxygenation in the brain. In recent years, many studies have pointed to a hallmark of autism which is local overconnectivity of the brain and distant reduced cortical connectivity. Meaning, the autistic brain [in general] has atypical reduced communication between distant neurons, and increased connectivity to nearby neurons. In other words, rather than being impaired in neurologic communication, the autistic brain may be considered to be specialized.


All that being said, Autism is a SPECTRUM disorder and is incredibly variable - in the behavioral symptoms, symptom severity, mutations and gene expressions present, the cortical volumes, and physiological connections between neurons.


This idea that autisms hallmark is a variety of differences is strongly emphasized by the researchers, and it explains why there is so much inconsistency in fcMRI research. All of the recent fcMRI research is valuable, but there are too many variables at play to draw conclusions between a whole brain scan and symptom severity. As a result, while one researcher may find increased connectivity in region A of the brain, another may find decreased activity in region A. This is due to the spectrum of brains people with autism can have.


These researchers had 16 groups of mice with different mutations. After completing fcMRIs on the mice, the researchers were able to group the 16 mutation groups into 4 similar groups with specific patterns of connectivity.


Figure 4. Shown in blue are regions of the autistic brain that are underconnected compared to controls, and red regions are overconnected compared to controls.


Notice how in this figure, multiple mutations (ie FMR1.1 TREM2) are able to be grouped together due to their similar connectivity, but that they are dissimilar to other clusters. This is indicative of the inconsistent results researchers have been finding.


This study is a massive leap in the research of autism. It suggests that some mutations present in autism are associated with similar connectivity alterations, and others may be associated with opposite alterations. This may provide guidance to researchers and clinicians who seek to associate these brain maps with etiology.



CITATION:

Zerbi, V., Pagani, M., Markicevic, M., Matteoli, M., Pozzi, D., Fagiolini, M., Bozzi, Y., Galbusera, A., Scattoni, M., Provenzano, G., Banerjee, A., Helmchen, F., Basson, M.A., Ellegood, J., Lerch, J., Rudin, M., Gozzi, A., & Wenderoth, N. (2020). Brain mapping across 16 autism mouse models reveals a spectrum of functional connectivity subtypes. bioRxiv.




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