What Causes ADHD?
What Causes ADHD?
What Causes ADHD?
In a previous post on my blog I described how the pseudoscience and scare journalism about ADHD can lead to lack of adequate treatment for kids and years of unneeded frustration for families. At the end of the post I proposed an antidote to the fear and pseudoscience: learning what credible peer-reviewed research has to say about ADHD. This post presents some of the findings from that body of research.
Contrary to popular opinion, ADHD is not a new phenomenon. In fact, the first mention of it in the medical literature is found in 1798 in a book by the Scottish physician Sir Alexander Crichton, who dedicated a chapter of the book to "Attention and its Diseases."
In his description, Crichton framed the hyperactivity and inattention he saw in some patients as primarily a disease of the nervous system—a problem with how one is wired. Since that time other doctors have also independently noticed the same thing (Hoffman in 1844, Still in 1902, and Tredgold in 1908) and each intuitively framed it in just the same way that Crichton did, as a biological problem rooted in the nervous system.
An amazing thing has happened in the past two decades: we may have found that these early intuitions about ADHD are correct. It's a rare instance in which science has confirmed first impressions.
The current research is most consistent with the theory that ADHD is a biological problem; however, scientists are still working to sort out what biological pathways lead to ADHD. The most current research suggests that ADHD is "multidetermined," meaning that there are likely many different biological causes. There are several independent lines of research that conform to this explanation: genetic studies, environmental studies and brain imaging studies.
Genetic Studies: The research in this area is very strong, has been replicated many times, and consistently supports the theory that there is a genetic component to ADHD. A meta-analysis of genetic studies found that about 76% of the risk for ADHD is due to genetic influence. This fits with the repeated finding that parents with ADHD (whether mothers or fathers) have a much higher likelihood of having a child with ADHD. It is usually the case that when I work with a child who has ADHD, a close relative (often mom or dad) has it too.
The gene or genes have not been isolated yet, but the most recent studies are zeroing in on two likely candidates, both responsible for dopamine production. One study was able to directly link problems in a gene with the not-so-exciting name of "DRD4" with thinner tissue in the area of the brain responsible for regulating attention and controlling behavior.
- Environmental Studies: In addition to the genetic studies, other epigenetic and neurological research has found a relationship linking prenatal exposure to cigarette smoke and alcohol with ADHD. Other toxins in the environment may play a role as well, but research is still trying to isolate the most likely culprits. Along with toxins, some researchers have found evidence for a connection between ADHD and prenatal stress. Others have also found connections between ADHD and severe neglect in early childhood. While this research is promising, there are fewer studies in this area than in the genetic research, because it is more difficult to study.
Brain Imaging Studies: This line of research is striking because, thanks to some amazing technology, we have been able to watch living brains in action for the first time in history. Most people are familiar with this information because images of the brains of people with ADHD are strikingly different from those without it. In particular, the images consistently show that the part of the brain that is responsible for regulating attention, thinking ahead, planning, and prioritizing tasks appears "thinner" and less active in people with ADHD. It is believed that this part of the brain develops at a rate that is slower than would be expected in kids with ADHD, but often catches up in adulthood, which is why some people "outgrow" ADHD.
This video is a parent-friendly quick summary of the neurological research on ADHD by one of the leaders in the field. I wish there were more like these!
ADHD is biological condition. Just like asthma, diabetes, or epilepsy, it is not willful or the fault of the child (or the child's parents!). It can literally be seen in the brain through imaging techniques and is most likely caused by genes and/or exposure to hazards during critical developmental periods. Just like many other biological conditions, there is no cure at this time, but there are tools to manage the symptoms. Getting proper treatment that addresses the biological symptoms can prevent ADHD from becoming a disabling condition. In the same way that a child with poor eyesight can get glasses and sit closer to the board, a person with epilepsy can avoid flashing lights and manage stress, and a person with diabetes can monitor the sugar content of foods and take insulin, a person with a biological understanding of ADHD can learn what actions to take to reduce the impact of the symptoms on her life. There are many effective treatment options, and it is a good idea to see a professional to determine what combination of evidence-based treatments are the best fit.
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