Alcoholism and genetic variation

Variations in the gene for serotonin transport may affect drinking habits in alcoholics, according to Neurobiology Prof. Ming D. Li’s recent study. Li said he hopes information collected during the study will contribute to the development of better alcoholism treatments in the future. Working with 275 alcoholics, Li and his colleagues studied six single nucleotide polymorphisms, variations in the sequence of DNA, and found that a region on one SNP variant showed a significant association with the volume of drinks that alcoholics consume. The variant may influence serotonin levels in the brain, Li said, noting that scientists believe human bodies use serotonin for emotion and mood regulation, REM sleep and other various brain mechanisms. Researchers have found that alcohol increases serotonin levels in the brain. One hypothesis, Li said, is that if a variant in the gene for serotonin transport deprives alcoholics of serotonin, alcoholics may start drinking to alleviate the deficiency. Li said scientists for years have drawn a correlation between this particular gene, which controls serotonin transport, and alcoholism. Until now, however, no one had discovered a direct connection between variations in the gene and alcoholic behavior. Li said when an SNP changes the expression level of a gene and results in a change in function, it is defined as a “functional variant.” His research demonstrated that a functional variant can affect behavior, he said. “The whole human genetic feud is about trying to find what genetic variant is important,” Li said. The study focused on how the gene for serotonin transport affected the volume of alcohol consumed. “If you take alcoholics, they’re a very heterogeneous group,” research associate Chamindi Seneviratne said. “There are differences in their drinking, so what we wanted to do was to see if we could subgroup them into a higher drinking alcoholic group and a group that’s not drinking so heavily.” Seneviratne said she defined a heavy drinker as a male who consumes more than five alcoholic drinks per day or a female who consumes more than four. All of the test subjects were classified as heavy drinkers, she added. The study found that if an alcoholic has the variant in his or her serotonin-transport gene, he or she has a higher risk of consuming more alcohol than a person without it, Li said, noting that knowing more about these genetic variations will allow researchers to determine how to better treat individuals. Li said anti-depressants could assist in treatment because these drugs make more serotonin for the brain. The study also examined potential differences between men and women. Though previous studies have suggested that estrogen levels in females play a role in the expression of the serotonin-transport gene, Li and his colleagues found no difference in the variant between men and women. The research group does not, however, know whether the functional variant spans ethnic groups. Seneviratne said all of the individuals studied were of European descent. “According to research published in different areas, we have seen that there are different frequencies of different genotypes among different ethnic groups,” Seneviratne said. Li also stressed the importance of further research in the ethnic aspect of the study. “We don’t know if there would be differences,” Li said. “Right now, it is important to see if this variant is functional in other ethnic groups."