- Kristen Stuppy, MD
Genetics of ADHD
Updated: Apr 3, 2021
I have recently written What is ADHD? Why do some develop it? and What does brain imaging tell us about ADHD? Both of these help to show that ADHD is NOT caused by bad parents, bad kids, or many of the other things that are blamed. It is a disorder of brain development that has a genetic basis. Today we’ll go into some of the genetics of ADHD. My hope is that by learning how and why ADHD develops, we can stop blaming people for acting the way they do and treat the symptoms to help individuals thrive.
A bit about studying genetics
Twins are often used to study the inheritance of medical conditions because they have similar genetics and environment. Twin studies have shown that ADHD has a genetic link 70-80% of the time, but we haven’t identified a specific gene previously.
It has been thought that a range of small and hard to identify differences in the sequence of nucleotides, which are components of DNA, combine to increase the likelihood of ADHD. These single nucleotide polymorphisms are referred to as SNPs. Environmental factors play a greater or lesser role (or sometimes none at all) depending on exactly which genetic variations are present.
What are SNPs?
SNPs are commonly pronounced like the word “snips”.
They are the most common type of genetic variation among people. Each SNP represents a difference in a single nucleotide in our DNA strands.
SNPs occur normally throughout a person’s DNA. They occur once in every 300 nucleotides on average. There are about 10 million SNPs in the human genome. They can act as biological markers, helping scientists locate genes that are associated with disease. When SNPs occur within a gene or in a regulatory region near a gene, they may play a more direct role in disease by affecting the gene’s function.
Does this cause a problem?
Most SNPs have no effect on health or development.
Some of these genetic differences have been shown to be very important in the study of human health. SNPs that may help predict an individual’s response to certain drugs, susceptibility to environmental factors, and risk of developing particular diseases. SNPs can also be used to track the inheritance of disease genes within families.
For an interactive way to look at SNPs, see Learn Genetics.
What does the study show?
A new large study has shown 12 specific differences that link to ADHD. Size is important. If a study is of only 100 people, the results could be very skewed. This study included 20,183 people diagnosed with ADHD and 35,191 controls without ADHD. This large size increases the reliability of the study.
Twelve SNPs were identified that are linked to ADHD, but we must still learn what this means in terms of development of ADHD. Much like some people have a genetic predisposition to cancer but never develop cancer and others without a genetic risk still develop cancer, some people can have the SNPs without ADHD and some people without these SNPs can develop ADHD.
How can this help us?
ADHD is real
One important thing that genetic studies can do is to help people understand that ADHD is a real condition. It is not made up. Yes, it can be over diagnosed in some people and missed in others, but it is real either way.
Learning about symptoms
Comparing this study with similar ones of related conditions can lead to new understandings of relationships of the conditions.
For example, one SNP pattern found overlaps with those discovered in a similar study of insomnia. Many people with ADHD suffer from sleep problems, so this might lead to specific treatments of sleep disturbances.
Limitations of the study
This is not a study that will help us diagnose ADHD.
Specific ways that the genes lead to symptoms are not yet known.
How other factors, such as prematurity, nutrition, and life experiences, interact with the genetic predisposition must be further investigated.
How is ADHD diagnosed?
Diagnosis of ADHD requires that symptoms exist in at least two settings, such as home and school.
Standardized assessment scales should be used to assess risk of ADHD. These scales are commonly done by parents, teachers, and others close to a child. Adult rating scales are available for adults with suspected ADHD.
Evaluation to assess for other disorders and conditions that can mimic ADHD, such as learning disorders, sleep deprivation and anxiety, should be completed.
Blood tests and brain imaging are not required to diagnose or treat ADHD.
Future research may help us learn to manage the symptoms of ADHD in new ways.
My hope is that learning the causes of ADHD will not only help us manage the non-desired symptoms, but also cultivate the beneficial attributes and decrease the stigma and misunderstanding so we can help people with ADHD learn to thrive.