Exploring the Causes of ADHD
Experts are not in agreement on what causes ADHD. There are several theories. One leans more towards heredity and genetics, while the other focuses on multigenerational family stress and social stressors. What we know for sure is that the brain does not develop executive functioning skills as well as it could, causing the symptoms folks experience. ADHD is currently labeled as a neurodevelopmental disorder, meaning it can be diagnosed in childhood and lasts throughout the lifespan. It impacts the development of the nervous system and prefrontal cortex.
Genetic Factors
We know there is a genetic component to ADHD, and you are more likely to be diagnosed if a family member has a diagnosis. Experts disagree on how strong the heritability link is, with estimates ranging from 30 to 80%. It is expected that as more adults receive diagnoses and our understanding of ADHD improves, this will become clearer. While there is a strong genetic link, there is also a lack of clarity on how this impacts the severity of symptoms, and environmental elements do play a role.
Several candidate genes have been linked with ADHD, mainly those related to dopamine, serotonin, norepinephrine, and other neurotransmitter systems. Genes involved in synapse formation are also impacted, affecting the way the prefrontal cortex functions. Despite our expanding understanding of the causes of ADHD, it is still difficult to implicate a specific gene, as ADHD is so complex.
Environmental Influences
While it is still difficult to establish a causal relationship for ADHD, we are now starting to understand that many risk factors may correlate with an increased incidence of ADHD. The following is not an inclusive list but includes factors known to correlate with ADHD.
Prenatal and Perinatal Risk Factors
Alcohol and tobacco use
Opioids and acetaminophen
Stress and trauma
Oxygen deprivation during delivery
Prematurity or low birth weight
Postnatal Environmental Factors
Lead exposure
Head injuries
Childhood trauma
It is important to note that exposure to any of these factors does not guarantee ADHD. There is an unidentified element that, in combination with risk factors, increases the likelihood of an ADHD diagnosis.
Neurobiological Factors
There are several differences observed in ADHD brains compared to neurotypical brains. The cortical network tends to be less thick, especially in areas linked to the ability to maintain focused attention. The cortical network also tends to mature more slowly. Some areas of the brain, including the amygdala and hippocampus, may appear smaller and play a role in emotional regulation.
Through the use of functional MRIs, we can now see that those with ADHD show reduced activity in areas related to executive functioning, such as planning, timing, and working memory. Differences are also seen in areas related to emotional control and motivation.
It is important to note that difference does not mean deficit. We are learning more about brains every day and do not yet understand all the impacts of what we are observing.
Conclusion
As this post shows, there is a complicated relationship between genetics, environment, and neurobiology. We are still not clear on exactly what combination of variables causes ADHD or how the severity with which it is experienced changes. As more research is dedicated to understanding a more diverse experience of neurology, hopefully we learn more and create space to not only accommodate differences but also bring awareness to the unique gifts that come with all types of brains.
