Background: Research has demonstrated that autism spectrum disorder (ASD) is highly heritable, suggesting a genetic basis. However, within pairs of identical twins—who have the same DNA—one sibling can have ASD, while the other doesn’t. That discordance points to the possibility of epigenetic factors, or those related to the variable expression of DNA, linked to the disorder.

What’s New: On April 23, 2013, the journal Molecular Psychiatry published a study analyzing epigenetic differences in identical twins, as related to ASD. The researchers took blood samples from 50 pairs of identical twins—with matching ASD diagnoses, mismatched ASD diagnoses, or matching typical development. They found variations in DNA methylation patterns—a form of epigenetic modification—at certain regions in the genomes between identical twins with different severities of autism. DNA methylation can be viewed as a mechanism to fine-tune gene expression. While identical twins have the same DNA sequence, their methylation patterns can fluctuate, potentially resulting in different diagnostic outcomes.

Why it’s important: This is the first large-scale study to examine the relationship between ASD and epigenetic differences in twins. The findings could point the way to treatment and prevention strategies based on patterns of DNA methylation.

What are the Genetic Risk Factors for Autism?

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