There is so much discussion online about possible causes of ADHD – watching too much TV, eating too much sugar, lax parenting, schools that don’t allow for enough creativity or physical activity, etc. Surprisingly, one of least discussed topics is the connection between our genes and ADHD. We know that genes strongly influence our appearance, our intelligence, our athletic ability, and even our personality, so why not ADHD symptoms as well?
Decades of research have in fact established that genes play a significant role in the development of ADHD. For parents of kids with ADHD, it’s probably not surprising to hear that ADHD often runs in families. Most children with ADHD have at least one close relative with the disorder, and one-third of fathers with ADHD have a child who has ADHD themselves. The strongest evidence for the role of genes in the development of ADHD comes from studies of identical twins. Researchers have found that if one twin has ADHD there is a 90% chance that the other twin will have ADHD as well. This is compared to a 25% chance among non-identical siblings. Overall, scientists estimate that ADHD has a heritability factor of .76, meaning that genes are responsible for about 76% of the differences that contribute to the development of ADHD. For comparisons sake, genes are responsible for about 70% of individual differences in IQ, with the remaining 30% being determined by non-genetic factors, like access to high quality early education. As with IQ, whether or not an individual develops ADHD is largely influenced by genetics. However, environmental, or non-genetic, factors also play a role. These factors include exposure to toxins, maternal smoking during pregnancy, and premature birth (among others). If a child is exposed to one or more of these environmental factors, then he or she is at risk for developing ADHD. If a child is exposed to these environmental factors and he or she also carries genes that predispose him or her to ADHD, then his or her likelihood of developing the disorder increases significantly.
If we know that genes play an important role in the development of ADHD, is a genetic test available? Many parents ask this question, and why not given that genetic testing exists for many medical disorders and even for ancestry DNA profiles? While scientists can confidently establish a genetic basis for ADHD from twin and family studies, identifying specific genes associated with the disorder is a much more challenging task. ADHD affects multiple parts of the brain and impacts a wide range of cognitive functions. No single gene or chromosomal region is responsible for all ADHD symptoms. Instead, multiple genes make small contributions to the development of the disorder. Researchers have identified a few of these genes already, but they have a long way to go before they have a clear genetic picture of ADHD. So, currently no genetic test for ADHD is available.
Despite not yet having a clear understanding of every piece of the ADHD genetic puzzle, researchers are optimistic about where this line of research is headed. In the future, scientists may be able to conduct genetic testing that will measure ADHD susceptibility, even in very young children. This testing would open the door for prevention and early intervention opportunities that could greatly improve the lives of children and families who are at risk. Equally as exciting is the possibility of using precision medicine, which optimizes treatment based on an individual’s genetic profile, to tailor ADHD medications and behavioral interventions for each child. This could greatly reduce the amount of trial and error involved in finding the “right” ADHD medication or the most effective behavioral and cognitive interventions.
Understanding that ADHD is strongly influenced by genetics should help parents recognize that they are not “to blame” for a child’s symptoms. There is, however, a great deal that parents can do to help their child manage their ADHD and reach their full potential. In the future, with access to a clear picture of each child’s unique ADHD genetic profile, parents, teachers, and healthcare professionals will have the ability to be even more effective with the interventions they use to support children with ADHD.
Mary Rooney, Ph.D., is a licensed clinical psychologist in the Department of Psychiatry at the University of California San Francisco. Dr Rooney is a researcher and clinician specializing in the evaluation and treatment of ADHD and co-occurring behavioral, anxiety, and mood disorders. A strong advocate for those with attention and behavior problems, Dr. Rooney is committed to developing and providing comprehensive, cutting edge treatments tailored to meet the unique needs of each child and adolescent. Dr. Rooney's clinical interventions and research avenues emphasize working closely with parents and teachers to create supportive, structured home and school environments that enable children and adolescents to reach their full potential. In addition, Dr. Rooney serves as a consultant and ADHD expert to Huntington Learning Centers.
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