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Neuroimaging Identifies an Endophenotype and Candidate Biomarker for Autism

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In response to facial expression of emotional, a similar pattern of brain activity is observed in both people with autism and their unaffected siblings. Researchers from the University of Cambridge recently used functional magnetic resonance imaging (fMRI), a specialized MRI scan used to measure the change in blood flow related to neural activity in the brain, to show that reduced activity in areas of the brain associated with empathy and face processing is a candidate biomarker for familial risk of autism. The findings were published online yesterday in the journal Translational Psychiatry.

Siblings of individuals with autism have greater than 20 times the population risk of autism. Moreover, unaffected first-degree relatives display subtle impairments in the cognitive domains characteristically affected by the disorder, including atypical implicit response to facial expression of emotion, which suggests that the trait can be passed from parent to child.

An endophenotype is a heritable marker of familial risk for a condition. It co-segregates with the condition in families and is present in affected individuals regardless of whether their condition is displayed. It is also present in unaffected family members at a higher rate than in the general population.

In the study, scientists used neuroimaging to measure the neural response to facial expressions of emotion in adolescents with autism, their unaffected siblings and controls with no family history of autism to distinguish between neurobiological markers associated with familial risk and those associated with the condition itself. The goal was to use neurobiological markers associated with familial risk to identify candidate endophenotypes of autism.

Researchers studied 40 families consisting of a teenager with autism and a sibling without autism. They also evaluated 40 teenagers with no family history of autism. Each of the 120 participants was given an fMRI scan while viewing a series of photographs comprised of happy faces, fearful faces, neutral faces and fixation crosses.

In response to emotional vs. neutral faces, the investigators found that there was decreased activity across a range of brain areas — including those associated with empathy, understanding others’ emotions and face processing — in autism compared with controls. The response also differed significantly but to a lesser degree of impairment than autism in unaffected siblings compared to controls.

Because neural activity was attenuated in autism compared to unaffected siblings, and both were significantly decreased relative to controls, the results suggest that the differences in brain activity have a genetic basis that is shared between family members.

Dr Michael Spencer, lead author on the study, explained why only one of the siblings might develop autism when both have the same biomarker:

It is likely that in the sibling who develops autism additional as yet unknown steps — such as further genetic, brain structure or function differences — take place to cause autism.

Study: A novel functional brain imaging endophenotype of autism: the neural response to facial expression of emotion