Not all alcoholics are created equal. People differ in why they drink, how they drink and what effects drinking will have on their health and relationships.

A key biological component of the variability in alcoholism may be in the control of signaling by serotonin, a brain chemical that carries messages between nerve cells and mediates the rewarding effects of alcohol.

Scientists at the University of Virginia have found that a variation in the serotonin transporter gene, which regulates serotonin levels, is associated with drinking intensity. The results, which will appear in the February 2009 issue of Alcoholism: Clinical and Experimental Research, were published online yesterday.

Senevirante et al tested six variations in the serotonin transporter gene for association with drinking intensity in 275 alcoholics seeking treatment — 165 were Caucasian and 110 were Hispanic. Women made up 21.5% of the sample.

In the Caucasian sample only, the researchers found that having one or two copies of a C at rs1042173 led to less intense drinking, defined as number of drinks per drinking day. There was no difference in number of drinks averaged over 90 days. People with the AA genotype drank an average of about 11 drinks per drinking day, while those with the AC or CC genotype drank about eight and a half.

(23andMe customers see their data for rs1042173 using the Browse Raw Data feature)

Previous research has linked a separate variation in the serotonin transporter (5-HTTLPR) with alcohol dependence, but results have been conflicting.

The study’s authors point out that in all cases, the number of drinks people had exceeds the threshold for what is considered heavy drinking (five or more standard drinks per day for men and four or more for women). They also note that their study looked only at alcoholics seeking treatment, who may not be representative of alcoholics in general.

In the future, the researchers say they hope to investigate whether rs1042173 can be used to provide more effective treatment for alcoholism by predicting whether medications that affect the serotonin system will work for an individual.

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In the current issue of The Journal of Politics, Fowler and Dawes identify particular variants of the MAOA and 5HTT genes, both of which are part of the biological pathway that influences mood, emotion and judgment, as being “significantly associated with the decision to vote.”

Based on the description above, it’s easy to see how the serotonin pathway can affect social behaviors. Serotonin is a chemical in the brain that can induce feelings of happiness. Studies have shown that MAOA and 5HTT have different functions on the pathway, and variants of each gene have been linked to particular behaviors.

For example, the version of 5HTT with a slightly shorter genetic sequence has been associated with producing low levels of serotonin. Studies indicate that the “short” version of the gene has been linked to conditions such as alcohol dependence and bipolar depression.

On the other hand, the “long” version has been linked to more positive traits such as longevity and competitiveness in athletes.

Similarly, MAOA has high- and low-activity versions. The high-activity version has been linked with restless legs syndrome while the low-activity version, which is also associated with producing low serotonin levels, has been linked to increased sleep apnea and more severe symptoms of autism.

Because the “long” version of 5HTT and the “high” version of MAOA have been correlated with social behaviors, Fowler and Dawes proposed these as candidate genes for voting participation. They then looked at population data from the National Longitudinal Study of Adolescent Health to find confirmation of their theory.

Known as Add Health, the study itself consists of data collected from more than 15,000 young adults who the researchers tracked for seven years between 1994 and 2001. Among the questions the now 18-26 year-old participants answered for the researchers toward the end of the study were how often they’d attended church services in the past year and whether or not they voted in the 2000 presidential election.

Fowler and Dawes based their conclusions on the data collected from a subset of 2,300 Add Health participants because information for six genetic markers, including 5HTT and MAOA, were also collected from them. They correlated the genetic information with the answers from the surveys to find out if their candidate genes would turn out to play a role in voter turnout.

Turns out they found a couple of links. “Having a high MAOA allele,” Fowler and Dawes wrote in their paper, “raises the likelihood of voting by about 5%. Among people active in their religious organizations, having a long 5HTT allele raises the likelihood of voting by about 10%.”

Given the age range of the study participants, and the timing, it’s worth asking some questions about these conclusions. Fowler and Dawes themselves note that the young adults might have been voting for the first time during the 2000 election; the historic significance of that contest might have been a motivator along with theoretically being genetically inclined towards pro-social behavior. Having older participants in the study might have been able to provide the researchers with a more constant voting behavior perspective.

What Fowler and Dawes don’t discuss, though, is the role of religion during the 2000 election. One study published last year found that 25 percent of the public said their voting decisions for the 2000 election were influenced by the religious media. Another study found that members of evangelical Protestant churches form tight social networks that promote civic involvement such as political participation within these communities.

In short, the correlation between the long 5HTT version, religious involvement and voting might be a little more complicated than Fowler and Dawes contend.

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