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Autism Coach

Identical Twins, Autism and Epigenetics

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Published July 8, 2014.

Why is that one identical twin has autism and the other does not? It very may well have to do with the switching on and off of genes through methylation. Genes are regulated by methyl groups that attach to the end of a gene to silence the gene or turn it on. Environmental factors such as pollutants in prenatal and early childhood development are likely to play a part according to the findings of the large study according to researchers at King's College in London and the University of Exer, Chloe Wong, Ph.D and Jonathan Mill, PhD.

Epigenetics, the switching on and off of genes without changing the underlying DNA code, is a relatively new but rapidly advancing field of research. Specifically, the researchers looked at DNA methylation, a mechanism that keeps genes locked in the off position or turns them on. Using advanced technology, they compared areas of DNA methylation across the genomes (entire DNA sequence) of 100 identical twins (50 pairs). In some cases, both twins had autism. In others, just one or neither was affected.“We identified distinctive patterns of DNA methylation associated with autism diagnosis, related behavior traits and increasing severity of symptoms,” says Chloe Wong. The researchers also note that some of the distinctive differences appeared in regions of the genome associated with early brain development. There preliminary research indicates that many of the twins with autism have many genes that are turned off or silenced that are turned on in the less autistic or neurotypical twin.

“That nearly a third of identical twins differ in autism symptoms makes clear that there are also nongenetic influences at play in some cases,” Dr. Wong comments. Though they share the same womb, identical twins can experience different stresses during pregnancy and birth, she notes. Along these lines, studies have associated increased autism risk with certain birth complications. Exposure to certain chemicals prior to conception, during pregnancy or during early infancy may also affect autism risk.

Still, the question remains, how do such nongenetic influences influence the development of autism? In recent years, research has suggested that they may do so through epigenetics. That is, by affecting the systems that turn genes on and off at the proper time and place. Preliminary research is suggesting that endocrine system disruptors found in man-made chemicals such as pesticides and plastics can cause epigenetic changes DNA in human germ cells, to DNA during prenatal development, and to DNA during infancy and early childhood.

Research into the intersection between genetic and environmental influences is crucial, Dr. Mill concludes. “Sometimes risky environmental conditions can be avoided or even changed,” he notes. Potentially, advances in understanding autism epigenetics might also advance the development of tailored treatments.