The researchers studied DNA gathered as part of the Collaborative Study on the Genetics of Alcoholism (COGA). In this multi-center study, people who have been treated for alcohol dependence and members of their families provide DNA samples to researchers, who isolated DNA regions related to alcohol abuse and dependence, as well as a variety of other outcomes.
Some of the participants in the study also took the Wechsler Adult Intelligence Scale-Revised, a traditional IQ test. In all, members of 200 families, including more than 2,150 individuals, took the Wechsler test, and those results were matched to differences in individuals' DNA.
By comparing individual differences embedded in DNA, the team zeroed in on CHRM2, the neuronal receptor gene on chromosome 7. The CHRM2 gene activates a multitude of signaling pathways in the brain involved in learning, memory and other higher brain functions. The research team doesn't yet understand how the gene exerts its effects on intelligence.
Intelligence was one of the first traits that attracted the attention of people interested in the interplay of genes and environmental influences. Early studies of adopted children, for example, showed that when children grow up away from their biological parents, their IQs are more closely correlated to biological parents, with whom they share genes, than adoptive parents, with whom they share an environment.
But in spite of the association between genes and intelligence, it has been difficult to find specific variations that influence intelligence. The genes identified in the past were those that had profoundly negative effects on intelligence ?genes that cause mental retardation, for example. Those that contribute to less dramatic differences have been much harder to isolate.
Dick's team is not the first to notice a link between intel
Source:Washington University School of Medicine