Thursday, September 15, 2011
All you need is love... and the right alleles
It's been called the "love hormone" because studies have shown that it is released during labor and breastfeeding. Children soothed by their mothers produce it, and, apparently, it has a role in easing social interactions. Oxytocin is a hormone secreted by the pituitary gland. It is a neurotransmitter, which basically means that it helps send signals from the brain to the receiving cells.
OXTR is the oxytocin gene receptor, in other words, this gene codes the protein that sits on the surface of the cell waiting to "grab" the oxytocin. So, if oxytocin has such beneficial effects on our behavior, it seems natural to look into this gene and see how it affects us, right?
That's exactly what a study published in this week's issue of PNAS  did. The researchers (from UCLA, UCSB, and Ohio State University) found one particular SNP in OXTR to be associated with three psychological traits: optimism, self-esteem, and mastery (the ability of making decisions, of being determined to achieve certain outcomes in life). This is an important finding, since the traits they found to be linked with OXTR are known to be correlated with positive health outcomes and good stress management.
Okay, let's back up a little. What's a SNP?
You and I share most of our DNA. We all do. There are very few loci where DNA differs across people, and SNPs are some of those loci. SNP (pronounced "snip") stands for Single Nucleotide Polymorphism, and it represents one particular base in the DNA that's found to be changing across the population (hence the "polyphormism"). It's a single base, but because we have two copies, it is represented by two nucleotides. The SNP found in the PNAS paper, for example, is represented by the following alleles in the population: AA, AG, and GG. In other words, when you look at people's DNA at that particular position, you'll find that some carry a GG, some an AG, and some others an AA. So how was the association found? The researchers recruited a number of subjects and found out which alleles they carried. Then they measured their psychological traits, and they saw that individuals that carried the "A" allele had a tendency to have lower levels of optimism, self-esteem, and mastery, and higher levels of depression.
Now to the caveats.
In general, looking at one SNP only gives a somehow limited picture. Genetics is not just DNA, rather a very complicated hierarchy of interactions, mechanisms, and cascade effects. Genes often interact and "combine" forces. For example, groups of multiple SNPs tend to be inherited together, and "piggy-back" mutations appear as an effect of chromosomal recombination. In this case in particular, this hypothesis seems plausible given the fact that the SNP under investigation is silent, hence does not affect the structure of the protein OXTR encodes. Furthermore, one must keep in mind that certain traits can be altered by epigenetic changes. Caveats aside, it is certainly fascinating to see how genes can affect our behavior and state of mind, and I look forward to the next papers from this group.
 Saphire-Bernstein, S., Way, B., Kim, H., Sherman, D., & Taylor, S. (2011). Oxytocin receptor gene (OXTR) is related to psychological resources Proceedings of the National Academy of Sciences, 108 (37), 15118-15122 DOI: 10.1073/pnas.1113137108
Photo: aspens at sunset. Canon 40D, focal length 81mm, F-stop 5.6, shutter speed 1/100. On a side note, those three aspens came down this summer. Too much wind, sadly.