What about ADHD genes?
We each have two copies of the serotonin transport gene, SERT, one from each parent. This gene regulates uptake of serotonin back into the cell.
The gene comes in two flavors, long (L) and short (S). If you’re lucky, you got LL. You are not very sensitive to stress and you’re unlikely to become depressed no matter what happens. You also have less anxiety.
With SS, you are very likely to become depressed in response to stress. With LS, you’re in between.
With early childhood stress, the frontal area of the brain does not develop as well. There is a lack of volume in the areas responsible for controlling response to stress and to unpleasant feelings and for controlling impulses.
If you have SS, you’re more sensitive to stress and this effect on your brain is more profound.
With SS things that are stressful to you will cause a bigger reaction than for your buddy with LL. He might not even find them stressful it all. On the other hand, if you have ADHD you might be creating more stress in your life.
Recent research shows that those of us with the combination of SS and more stress have less frontal brain volume and more severe ADHD symptoms. Those with LL have more normal frontal brain volumes and less severe ADHD symptoms, regardless of stressful life experiences. The frontal brain is where judgement and delaying action live.
With ADHD there is also less good connection between the regulating frontal areas and the stress responding lower areas (subcortical structures).
For most ADHD children the brain gets more normal with aging. Stimulants (ritalin, adderall, vyvanse, daytrana, etc.) also change brain structures toward normal in children and in adults.
We have to be careful about confusing cause and effect and remember that correlation does not prove causation. But these findings are very suggestive.
If ADHD is like most psychiatric disorders, and it probably is, then there is no one gene responsible, but many genes that contribute to a propensity to have the disorder. The environment and expericens may then determine to what extent those genes are activated.
I welcome comments from everyone but especially invite our scientists to correct any misinformation here. I don’t claim to really understand this stuff.
(http://ajp.psychiatryonline.org/doi/10.1176/appi.ajp.2011.11020281 in case the link doesn’t work)
Note: Actually, it’s even more complicated. Newer research suggests that the SS combination may even be of some benefit, IF you don’t have a very stressful childhood.
Link: serotonin transporter gene