Connecting Biology to Behavior: The Role of Genetics in ADHD

This post is the third in the series “Connecting Biology to Behavior: Inside the ADHD Brain.” Read the first post to learn about the role of dopamine in ADHD behaviors and the second post to learn about the role of the amygdala in the emotional dysregulation that occurs in ADHD.

We inherit eye color, hair color, and height from our parents, but can we inherit ADHD too? Over my time working with ADHD children and their parents, more often than not, parents will admit they realized their own ADHD after their child was diagnosed.

Understanding the genetic nature of ADHD will aid in accurate diagnosis, personalized treatment, and advancing research toward more effective therapies. In addition, recognizing that ADHD can run in families helps foster empathy, improve communication, and strengthen relationships by shifting the focus from blame to understanding.

Genetics and heritability

A child with ADHD is likely to have a parent, sibling, or close relative with ADHD, suggesting that ADHD can run in families. ADHD is likely caused by genetic factors, a mutation in a specific gene or genes, and is passed on, or inherited, from your parents. Therefore, ADHD can be considered a disorder that is both genetic and hereditary. In fact, estimates of heritability for ADHD range between 50 and 80 percent. If a child has ADHD, there is a 10 to 35 percent chance an immediate family member also has the disorder, and if the relative is a parent, there is a 57 percent chance the child will have ADHD. More support for the heritability of ADHD comes from twin studies, with 70 percent of twins sharing an ADHD diagnosis. Additionally, adoption studies suggest genetic factors are involved in ADHD, with rates of ADHD higher among biological relatives of non-adopted children than adoptive relatives of adopted children.

A recent study found that there may be up to 76 risk genes associated with ADHD. The authors describe the “polygenic architecture” of ADHD, meaning the genetic basis for ADHD is influenced by multiple genes, and estimate that as many as 7,300 common genetic variants influence ADHD. Interestingly, these genes are associated with early embryonic brain development. Additionally, variations of genes expressed in the frontal cortex and midbrain dopamine neurons were found, suggesting a role of genetics in executive function deficits common in ADHD. The study also reported a high rate of overlap, 84 to 98 percent, for genes that occurred in ADHD and other psychiatric disorders like depression, autism spectrum disorder, and schizophrenia, disorders that are known to co-occur with ADHD.

Beyond genetics: Environmental factors to consider

Nature vs. nurture remains a central question in psychology, as researchers strive to understand how biology and experience interact to shape human behavior. If the symptoms of ADHD were solely based on genetics, then we would expect the heritability rate among twins to be 100 percent; however, this is not the case, suggesting that environmental factors also play a role in ADHD behaviors. For example, childhood stroke or streptococcal infection, traumatic brain injury, and exposure to heavy metals like lead have all been found to be associated with ADHD. In addition, low birth weight, maternal stress, and alcohol consumption or smoking during pregnancy can also contribute to ADHD.

In contrast, a diet high in sugary snacks and soda is not an underlying cause of ADHD, but a healthy diet may be beneficial in reducing the symptoms of ADHD. Additionally, bad parenting does not lead to a diagnosis of ADHD. However, parental behavior as a result of interacting with an ADHD child may increase ADHD symptoms. For example, a cycle of a child not completing school assignments and getting bad grades, parents becoming frustrated, and then the child becoming frustrated can bring out symptoms of ADHD. When my ADHD son would forget to turn in assignments for school, I would get frustrated with him, he would yell at me, I would yell back at him, and then he would have a full-blown meltdown as a result of the emotional dysregulation that occurs in ADHD. I realized I had to modify my behavior that was contributing to my son’s emotional meltdowns.

A concern I often hear from parents is that their child is spending too much time on electronic devices, playing video games. Interestingly, time spent playing video games does not seem to cause ADHD or increase symptoms in children with an ADHD diagnosis. However, children with ADHD do spend more time playing video games, likely due to their hyperfocus and the appealing nature of the fast-paced, quick-thinking, challenging situations present in some video games. It is also worth noting that online video gaming may provide a safe space for social interactions for ADHD kids with lagging social skills; they have a sense of belonging and something in common with others. However, parents need to monitor online sites where their child is gaming and set parameters around time spent playing video games.

Although environmental factors can contribute to ADHD symptomatology, it remains largely a neurobiological disorder.