ADHD Gene #6: Serotonin Receptor 1B (HTR1B), human chromosome #6 (section q13)
This is our sixth gene of topic in our discussion of ADHD genes. The Serotonin Receptor 1B gene (HTR1B). Like the 5 ADHD genes previously discussed, the gene HTR1B is thought to have at least some influence on the development of ADHD. (If you would like some more background information on what genes, chromosomes, DNA and alleles are, and how they relate to ADHD, please check out this link to another section of the blog here. I have outlined some of the specifics in this area). As its name suggests, this gene is responsible for creating a specific binding site (or think of a "docking site"), for the important neurochemical serotonin. Essentially, there are multiple forms of this gene, which is located on the 6th chromosome in humans (the "q13" refers to a more specific location of the gene on the chromosome, if you would like further explanation on how this looks, please click here).
As mentioned in another post, sometimes the smallest changes in DNA can produce noticeable results in the resulting biology, and ultimately, behaviors, of an individual. This gene appears to be no exception. At one specific point of this serotonin receptor gene (HTR1B), some individuals have a DNA base of "G" (short for "Guanine"), while others have the DNA base of "C" (short for "Cytosine", for more info on what this means, please click here). It appears that the simple change of one small piece of DNA from a "C" to a "G" on this particular "ADHD gene" can have a significant effect with regards to ADHD. Individuals with the "G" form of this particular gene are statistically more likely to have ADHD than those with the "C" form.
Furthermore, the connection with ADHD seems to be strongest to a particular subtype of ADHD. Individuals with the "G" form, or allele, tend to exhibit behavior that is more concentrated on what is referred to as the inattentive subtype of ADHD. The inattentive subtype, as its name suggests, is a form of ADHD in which the inability to maintain attention for a necessary period of time is the dominant negative attribute of the disorder (in contrast to other subtypes of ADHD, which have a more concentrated impulsive component, and/or hyperactive components, which are highlighted by highly impulsive or hyperactive behavior, respectively). While other genes may be tied to these other types of ADHD, the "G" form of the HTR1B serotonin receptor gene appears to be significantly correlated primarily with the inattentive ADHD subtype.
Please remember that the "G" form of this gene is not some weird mutation or genetic malfunction. It is a perfectly common form of the gene that is found in a number of regular individuals. Furthermore, there have been several studies done on this form or allele of the HTR1B gene, including one done on fraternal twins that did not show a significant correlation between the "G" form of the gene and the frequency of ADHD. Nevertheless, the data from several other studies, when pooled together, have strongly suggested a significant statistical correlation between the "G" form and the likelihood of exhibiting inattentive ADHD behavior. In other words, we should be cautiously optimistic about this association. Keep in mind, however, that the presence of this form of the gene, or any of the previously discussed "ADHD genes" does not, single-handedly, "doom" an individual to ADHD, it simply means that individuals with this form of the gene are statistically more likely to develop ADHD. We will be wrapping up this section of posts on ADHD genes with the seventh and final ADHD gene, the SNAP 25 gene, in tomorrow's blog.
Wednesday, September 24, 2008