What if we were able to predict who was most likely to develop Alzheimer’s disease in older adults or ADHD in children -- even before the cognitive or behavioral symptoms of these disorders began to develop? How might we better treat, slow down, or perhaps even prevent these conditions from fully developing if we had advanced warning? Well, scientists studying biomarkers are trying to do just that, not only with ADHD or Alzheimer’s disease, but with a range of other conditions as well.
The search for biomarkers is a hot topic in science and research these days. The term biomarker, a fusion of “biological markers,” means a key indicator that signifies the presence or future probability of someone developing a medical or behavioral disorder. The benefits of having advanced warning are pretty self-evident, whether we are talking about reliable biomarkers for dementia or cancer, or for neurodevelopmental disorders like autism and ADHD.
So are there biomarkers for ADHD? And if so, what might they tell us?
Well, a few recent studies have given us some interesting points to ponder. Since ADHD is a developmental disorder that must first emerge in childhood or early adolescence (it cannot first be seen in adulthood), the search for ADHD biomarkers is focused on children. ADHD is also diagnosed more in boys than girls, and so some of the studies reflect this gender disparity as well. And while this research is heavily focused on ADHD in youngsters, the importance of this work for adults with ADHD is significant, as it can tell us a lot about the disorder over the whole life span.
One recent study on possible ADHD biomarkers comes from China. It involves a modification of MRI scanning into what is called functional brain imaging, to look for differences in brain activity in boys who have ADHD compared to boys who do not have the disorder.
Brain Activity and ADHD
A study just published in the April 2014 edition of the journal Radiology by Qiyong Gong and colleagues in China suggests that functional MRI scans might provide reliable, early detection of ADHD. This special version of MRI allows scientists to look at some broad types of real-time functioning (like metabolism), rather than just the structure of the brain, like a regular MRI does. In other words, it is more like watching a very slow video of what the brain does, rather than just a snapshot of what the brain looks like. The research team compared brain activity in 33 boys, ages 6 to 16, who had ADHD against 32 same-aged boys who did not have ADHD. The scientists found that the boys with ADHD had more functional abnormalities in several brain regions and circuits that are known to be involved in planning and controlling impulses and behaviors.
For anyone with ADHD this should hardly come as a surprise. Although “attention deficit” is in the name of the disorder, people with ADHD very often struggle not only with focus and distractibility, but also with time management, organization, and impulse control.
Other Biomarkers and ADHD
An earlier article about possible biomarkers of ADHD looks elsewhere. These scientists do not focus on the big picture MRI results of the last study discussed above. Rather, they bring it down more to the cellular level.
A review of the science on ADHD biomarkers by Catia Scassellati and a team of Italian and American colleagues mentions some other biomarkers for ADHD. Their paper is a systematic review of other previously published studies on the topic, and it was published in 2012 in the Journal of the American Academy of Child and Adolescent Psychiatry. They concluded that a number of possible biomarkers might be linked with symptoms of ADHD, including the neurotransmitter norepinephrine; an enzyme called MAO that deactivates neurotransmitters like dopamine, epinephrine, and norepinephrine; cortisol; and zinc. The neurotransmitters mentioned above are not specific only to ADHD; they have been associated with a range of other disorders from depression to schizophrenia.
Some other possible biomarkers of ADHD, although more studies are needed, include a chemical often linked to food intake (Neuropeptide Y) and DHEA. Bodybuilders and sports fans might have heard of DHEA before. It has been hyped as a muscle-building agent and has been banned for use by some collegiate and professional sports organizations. According to MayoClinic.org, DHEA is an adrenal hormone that spurs the production of some male and female hormones. So it is easy to see why it would be forbidden in athletics. As a possible biomarker, lower levels of DHEA are correlated with ADHD, but like all of these other findings, that does not necessarily mean that DHEA causes ADHD. Low DHEA levels are associated with depression, heart disease, and natural aging as well. Rather, there might be a possible association between DHEA (or any of these other mentioned substances) and ADHD symptoms without it necessarily being a cause of the symptoms.
So What Does This Mean?
The potential power of a biomarker for any other condition is that it may help us to better identify who is at risk of developing a disorder early on. Currently, we consider that someone might have ADHD or Alzheimer’s disease only after symptoms have begun to develop. The search for biomarkers has also shown us how complicated and multi-dimensional the links and possible causes of most of these disorders actually are.
There is no silver bullet right now for identifying ADHD early. But in the future there may be, perhaps with a combination of reliable biomarkers considered together. For ADHD and most other conditions, biomarkers tend to be linked to the disorder without directly causing it. Contrast this with a truly causal relationship, such as the needing to contract the HIV virus to develop AIDS, or a certain genetic pattern being required in an individual in order to develop Huntington’s disease.
The future promises of biomarkers are to improve precision in diagnosis and to develop more effective or even preventative treatments early on. The search for biomarkers is in its infancy, and it holds a potential capacity for a better future in the identification and management of ADHD.