Andrew Chess and his colleagues are exploring a new way by which polymorphisms (small variations in the DNA sequence of a gene) can control gene regulation by influencing the addition of methyl groups to the DNA strand, impeding its expression. The researchers plan to explore whether and how a mechanism involving polymorphisms and methylation might be at work in autism. To analyze methylation across the genome, the researchers digest the entire genome using special enzymes that break the DNA strand at all potential methylation sites, except those that are actually methylated. The remaining DNA fragments can then be analyzed to determine which polymorphisms they represent. Chess and his team plan to use this technique to look for differences in methylation patterns between individuals with autism and healthy controls. They also plan to analyze identical twin pairs in which only one twin has autism in the hopes of uncovering a reason for the difference. The findings may lead to the discovery of genes that cause autism when their expression is altered by methylation.