Multimodal brain imaging in autism spectrum disorder and the promise of twin research.
Scanning identical twins who differ in autism could finally show which brain features are genetic and which are environmental.
01Research in Context
What this study did
Mevel et al. (2015) wrote a think-piece, not an experiment.
They say we should scan the brains of identical twins who share genes but not autism.
By comparing the twin with ASD to the twin without, we could see which brain differences are truly genetic.
What they found
The paper offers no new data.
It only argues that the "monozygotic twin connectome design" could finally split nature from nurture in autism.
How this fits with other research
Earlier twin work backs the idea. Murphy et al. (2014) showed that extreme autism traits are highly heritable, while a full diagnosis is only weakly heritable.
Dworzynski et al. (2009) found that social and repetitive symptoms have partly separate genetic roots.
Imaging reviews give the team something to look for. Duerden et al. (2012) list white-matter gaps in the corpus callosum and temporal tracts, and Seiverling et al. (2012) warn that brain data only partly match DSM-5 domains.
Taken together, the twin method plus connectome maps could test whether those white-matter findings are driven by genes or life events.
Why it matters
If you assess or diagnose, keep an eye on twin-connectome studies. They may soon tell us which brain features are hard-wired and which might respond to early intervention. Until then, stay cautious when families ask if autism is "all genetic"—the answer is still unfolding.
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02At a glance
03Original abstract
Current evidence suggests the phenotype of autism spectrum disorder to be driven by a complex interaction of genetic and environmental factors impacting onto brain maturation, synaptic function, and cortical networks. However, findings are heterogeneous, and the exact neurobiological pathways of autism spectrum disorder still remain poorly understood. The co-twin control or twin-difference design is a potentially powerful tool to disentangle causal genetic and environmental contributions on neurodevelopment in autism spectrum disorder. To this end, monozygotic twins discordant for this condition provide unique means for the maximum control of potentially confounding factors. Unfortunately, only few studies of a rather narrow scope, and limited sample size, have been conducted. In an attempt to highlight the great potential of combining the brain connectome approach with monozygotic twin design, we first give an overview of the existing neurobiological evidence for autism spectrum disorder and its cognitive correlates. Then, a special focus is made onto the brain imaging findings reported within populations of monozygotic twins phenotypically discordant for autism spectrum disorder. Finally, we introduce the brain connectome model and describe an ongoing project using this approach among the largest cohort of monozygotic twins discordant for autism spectrum disorder ever recruited.
Autism : the international journal of research and practice, 2015 · doi:10.1177/1362361314535510