Week two the Coursera class on ADHD Through the Lifespan taught by Dr. Anthony L. Rostain, M.D., M.A. of the University of Pennsylvania is focusing on the causes of ADHD. The lecture was well put together and very informative. The reading is from Brain Facts, a free publication from the Society for Neuroscience.
I am getting more enthusiastic about the course now that we are starting to tackle some of the science of ADHD. Although diagnosing ADHD can be an exercise in subjective opinion more that unbiased reality, ADHD does have a biological basis. The problem is that it is a complex genetic disorder where various factors alter the neural pathways. It doesn’t follow simple Mendelian inheritance rules although it is one of the most inheritable psychiatric diagnoses. The mean heritability of ADHD is 0.75 this is almost the same as the mean heritability of height and greater than the heritability of asthma, high blood pressure, breast cancer, or alcoholism. As an aside, autistic-like traits are 0.82-0.87 inherited which is something to keep in mind with the increase in autism diagnoses over the last 10 years.
The best data tells us that 65-75% of ADHD is due to genetics and 25-35% is due to acquired central nervous system injuries. If a parent has ADHD, their child has a 40-54% chance of having ADHD. The chance of a child being diagnosed with ADHD skyrockets when both a genetic factor and an environmental factor are both present. Specific genes associated with ADHD are serotonin and dopamine receptors and transporters, and synaptosomal-associated protein 25. The different types of ADHD may be associated with different genotypes and specific ADHD medications may be more or less effective, depending on which genes are contributing to ADHD in a specific individual.
Taking all this together, I believe there are some strong implications for public policy and preventative parent education programs. For example, after heredity, the largest cause of ADHD is low birth rate. In fact, low birth rate by itself is associated with ADHD as much or more than fetal alcohol syndrome, lead exposure, and the mother smoking during pregnancy, combined. Parents with low birth weight children should be educated on ADHD while they are still in the hospital. They need to know that if one parent has ADHD and their child has a low birth weight, there is an increased likelihood that child may eventually be diagnosed with ADHD. They must also be given ideas and tools for how to help their child learn impulse control and organization skills.
It is interesting to note the increase in ADHD, especially in boys, seems to parallel the decrease in recess, walking to school, and physically active gym classes. We know that serotonin and dopamine are positively affected by exercise and exercise can alleviate ADHD symptoms. I am hoping that Dr. Rostain includes exercise as a treatment option. Many parents, especially of very young children with ADHD, are looking for ways to help their children without medication. Again, if parents are aware of the genetic+environment risk factors for ADHD, they will hopefully be more proactive in helping their kids get effective, regular exercise.
Just like with autism, early intervention and extra effort can lead to improved outcomes for individuals with ADHD. It seems it is far better to help kids proactively develop good habits and coping skills instead of letting untreated or acknowledged ADHD symptoms derail their academic and social lives.