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The World Federation of ADHD Guide 11 Epigenetics refers to a field of study that examines how the environment mo- difies the genome to change the expression of genes. Epigenetic modifications do not make change to the chemical structure of DNA. Instead, they use mechanisms such as methylation and histone acetylation to change how accessible DNA is to elements required to trigger its expression. Although all cells contain full genomes worth of DNA, every cell only expresses as small subset of that DNA, which is why we have cells with specialized functions such as dopamine neurons and glia. By controlling gene expression, epigenetic events allow for this specialization to occur. The importance of such mechanisms for ADHD is illustrated by the GWAS study finding that much of ADHD’s heritability is explained by SNPs in regions that regulate genes rather than in genes themselves. Although there are too few epigenetic studies of ADHD to draw firm conclusions, this area of research is like- ly to provide insights in the future. 27 SUMMARY: ENVIRONMENTAL CAUSES OF ADHD Substantial data from epidemiologic studies implicates the environment in the etiology of ADHD. These data implicate biological assaults on the developing brain such as exposures to toxins, maternal smoking, anoxic birth complications, mild traumatic brain injury and institutional deprivation. Psychosocial stresses such as marital distress, family dysfunction and low social class have also been implicated by epidemiologic studies. Although we expect that gene by environ- ment interaction and epigenetic effects mediate these environmental risks, these areas of research are not sufficiently mature to offer conclusive findings about the etiology of ADHD. DISCUSSION Although we have a long road to travel before fully understanding the etiology of ADHD, much progress has been made. We can be sure that some of the risk for Link in this http://additudemag.libsyn.com/188- beyond-genes-how-environment- and-lifestyle-impact-adhd