Is ADHD genetic?
As genetic screening and genomic sequencing continue to roll along, we have made a number of interesting discoveries about ADHD and potential ADHD treatment options. A 2006 article in the Journal of Clinical Psychiatry called "Candidate Gene Studies of Attention-Deficit/Hyperactivity Disorder" by Stephen V. Faraone and Sajjad A. Khan examined some of the studies on some of the specific genes that are affiliated with ADHD. A number of these genes relate to the manufacturing, transport and modification of two key compounds involved in the brain: serotonin and dopamine. Both of these play a critical role in regulating the attention span, imbalances of one or both of these are associated with different forms of ADHD.
***These next 2 paragraphs give a basic explanation of human genetics relevant to our discussion. If you are already familiar with the terminology, these two paragraphs may be omitted. If you would like additional background information on terms such as genes, alleles, DNA and chromosomes, and how they relate to our topic of ADHD, please click here.
Before we go any further, I just want to make sure that we are on the same page as far as discussing genes related to ADHD and its potential treatment options are concerned. If you are not familiar with genetics, a gene is simply a segment of DNA that acts as a "blueprint" to the body to manufacture specific proteins that ultimately determine hair color, eye color, and even built-in-resistances to certain diseases. For humans, there are about 30,000 different genes (this number, however, is widely debatable), which are scattered throughout 23 pairs (46 total) of chromosomes. This averages out to roughly 1000 different genes per chromosome.
It is important to note that while a specific gene is extremely similar amongst different people(down to a fraction of a percent difference), there are slightly different forms of the same gene, which vary from person to person. These different forms are called alleles of the gene. These alleles can result in some huge differences among different individuals and play a major role in the great diversity of our species. If an individual has a particular form (allele) of one or more of the seven genes listed above, he or she has a higher likelihood of exhibiting ADHD behaviors. For those interested, genetic screening is available to see if an individual possesses one or more of the "ADHD alleles" for seven different genes listed below.
Seven genes that are thought to be tied to ADHD are as follows:
ADHD gene #1. Dopamine D4 receptor gene (DRD4)
ADHD gene #2. Dopamine D5 receptor gene (DRD5)
ADHD gene #3. Dopamine transporter gene (DAT)
ADHD gene #4. Dopamine beta-hydroxylase gene (DBH)
ADHD gene #5. Serotonin transporter gene (5-HTT)
ADHD gene #6. Serotonin receptor 1B gene (HTR1B)
ADHD gene#7. Synaptosomal-associated protein 25 gene (SNAP 25)
I will discuss each of these "ADHD genes" and how some of them are related to the various ADHD treatment options in more detail in my upcoming posts, so stay tuned!
Sunday, August 31, 2008