Based on the research that’s been conducted so far, there isn’t a single root cause of ADHD. There’s no way for medical professionals to provide a clear-cut explanation as to why some people have the disorder while others don’t. Instead, ADHD probably develops due to a combination of different factors.
One area that seems to influence the development of ADHD is genetics. Hereditary factors may be more significant contributors to ADHD than many people realize. Learn more about whether ADHD is inherited and how your family history might be at play when it comes to this disorder.
The Genetics of ADHD
There are a number of conditions that seem to run in families, like heart disease, high cholesterol, and some cancers. According to available evidence, ADHD can be counted among these genetic conditions. In fact, a child with ADHD is four times more likely to have a relative with ADHD compared to a child who does not have the condition. Furthermore, a third of fathers who had ADHD in their childhood have a child with ADHD.
Across a number of studies, this link between genetics and ADHD holds up. For example, one study focused on how much a parent’s diagnosis (or lack thereof) influenced the likelihood of their children having ADHD. It found that among parents where neither one has ADHD, 11% of the children had ADHD. That portion increased to 34% when one parent has ADHD. In short, there’s a strong familial nature to the disorder.
To come to these findings, scientists used data to determine the heritability of ADHD. Heritability is a measure of how much of a certain trait or characteristic can be attributed to genetic factors. For ADHD, the heritability factor is 0.77, with 1 being the maximum possible number. A heritability factor of 0.77 is comparable to that of schizophrenia or bipolar disorder.
Nature vs. Nurture
Some have argued that ADHD may also be partially attributed to the way that children are raised. These individuals believe that parenting style and household atmosphere play a role in the development of ADHD.
However, scientific findings generally don’t support this theory. If ADHD is attributed to “nurture” rather than “nature,” then the frequency of ADHD should be the same among siblings and half-siblings raised in the same environment. But studies have found that, compared to siblings, there is a significantly decreased frequency of ADHD among half-siblings.
Similarly, adopted children with ADHD have provided a window into the increased chances of having the disorder due to genetic factors. When an adopted individual exhibited antisocial personality, alcoholism, and ADHD, the rate of those same issues was significantly higher in their biological parents compared to their adoptive parents.
Studies involving twins have also been very illuminating when it comes to the ADHD nature vs. nurture debate. One study found that when one identical twin had ADHD, the other twin also had ADHD. Among non-identical twins, only 17% had ADHD when their twin had the disorder.
Environmental Factors Contributing to ADHD
Genetics are just one of the elements that may influence whether someone has ADHD. In addition, there are certain environmental factors which could also contribute to the development of the disorder. While the research in these areas isn’t decisive, it does point to other plausible considerations for the causes of ADHD.
Maternal drug and alcohol use
When a child is exposed to certain substances in utero, it could result in a higher risk of developing ADHD. One study found this to be the case among the children of mothers who used opioids during pregnancy. Those children had more than double the risk of ADHD compared to those whose mothers did not use opioids while pregnant.
Head trauma can have long-term effects, and some researchers are looking into whether ADHD can develop as a result. In one study, 62% of children with a traumatic brain injury (TBI) went on to develop ADHD. Among those who did not have a TBI, only 15% developed ADHD.
Psychological and social factors may play a role in the development of ADHD or potentially increase the severity of ADHD symptoms. Some of these psychosocial factors include unsupportive parents of primary caregivers, growing up in poverty, or being raised in a chaotic household environment.
Genetics are a major factor in the development of ADHD. However, they aren’t the only factor at play. Considering just how complex the disorder is and how many different types of symptoms can be involved in ADHD, it’s impossible to nail down one specific cause behind it. Instead, we can take into account the way various factors contribute to ADHD when looking for possible treatments.