DNA Offers Clue Into Why Some People Are More Sociable and Trusting

People are social animals. And, of course, some people are more social than others. Think Penny and Sheldon from The Big Bang Theory to get a feel for the range.

A new study has found a genetic difference that might explain at least part of this spectrum of sociability. It might even help us understand how someone can go from being shy as a child to outgoing as an adult or vice versa.

The gene involved, the oxytocin gene, makes perfect sense as it is intimately involved in sociability. It has the instructions for making the hormone oxytocin and this hormone forges bonds when falling in love, plays a critical role in mother-child bonding and improves people's ability to read emotions accurately in the face of another person. Oxytocin isn’t the whole story, but it is almost certainly a piece in these puzzles.

In this new study, the researchers collected the spit of 121 healthy volunteers and looked at their oxytocin gene. But the team wasn't looking at the A’s, G’s, C’s and T’s that have the genetic instructions for making oxytocin. Instead, they were looking at something that decorates the gene and affects how much oxytocin the gene says to make. That something is called methyl groups.

In general, the more methylation a gene has, the less active it is. And the less active it is, the less product it makes. So an oxytocin gene with a lot of methylation will make less oxytocin. And an oxytocin gene with just a little methylation will make more of it.

Methylation is not, in and of itself, a negative thing. It's a process that helps regulate gene expression so the body gets the right amount of hormones and other critical molecules in the cell. But it can go awry in ways that result in physical or mental disease.

What we do and how we live our life can affect the level of methylation on our DNA. We know that enzymes in the cells trigger methylation or demethylation, but we aren't always sure how our experiences causes those enzymes to start working in a specific way.

The researchers in the oxytocin study found that, most of the time, a more methylated oxytocin gene translated to less sociability in these healthy volunteers. They used a variety of tests to look at this.

The first test was a self-reported survey. The more anxious people said they were about their relationships, the more likely they were to have more methyl groups on the oxytocin gene in their DNA.

The second test checked how well people can read emotions on a person’s face. They were shown images of people becoming happy, sad, angry or fearful over a 10-second span of time and were asked to identify the emotion as soon as they were confident in the answer. More methylation meant longer times to tell when someone was getting angry.

The last tests looked directly at the brain. In one, researchers studied participants' brains in a couple of different ways while the participants thought about how other people might be feeling or what their point of view might be. Researchers found that, during this test, the parts of the brain involved in sociability were less active in people whose oxytocin genes were more methylated.

Taken together, this research points toward the idea that people with a more methylated oxytocin gene are less sociable. Which, if true, is something that can change over our lifetimes. And just might point to a way to treat people who are severely affected by their lack of sociability (think of people toward one end of the autism spectrum).

Sounds Good But…

This is all very exciting, but there are a few things to keep in mind.

First off, this was a small study: only 121 people. Scientific literature is littered with claims that didn’t hold up when applied to larger groups.

Secondly, researchers looked at the DNA in the participants’ spit. Genes often have different levels of methylation in different parts of the body (this is part of the reason a muscle cell is different from a brain cell, even though they have the same DNA). So what is true in spit may not be true in the brain. A study showed that DNA methylation in spit is closer to what's in the brain than is DNA in the blood, but it is still not the same.

Third, they didn’t directly look at the levels of oxytocin in the participants. Methylation usually weakens a gene, but not always.

Still, it is an interesting study, giving the first indication that methylation of the oxytocin gene plays a role in sociability. We’ll have to see if it pans out in a larger study. If it does, it might make for an interesting new target to go after for conditions where lack of sociability characterizes the illness.