May 30, 2013

Genetic variants linked to educational attainment

A multinational team of researchers has identified genetic markers that predict educational attainment by pooling data from more than 125,000 individuals in the United States, Australia and 13 western European countries.

The study, which appears today (May 30) in the journal Science, was conducted by the Social Science Genetic Association Consortium (SSGAC), which includes researchers at Cornell University, New York University, Erasmus University, Harvard University, the University of Queensland and the University of Bristol, among other institutions.

“We believe our study shows that a feasible and promising approach to social-science genetics is to use very large samples,” said Daniel Benjamin, associate professor of economics at Cornell and a behavioral economist who co-directs the SSGAC. “Our sample has 125,000 individuals. Previous studies have used much smaller samples – typically 100 to 2,000 individuals. If genetic associations with other behavioral traits have effect sizes as small as those in our data, then sample sizes need to be much larger to produce accurate findings.”

New group advances behavioral genetics research

The study is the first project of the Social Science Genetic Association Consortium (SSGAC), a research group designed to stimulate dialogue and cooperation between medical researchers and social scientists. The SSGAC facilitates collaborative research that seeks to identify associations between specific genetic markers (segments of DNA) and behavioral traits, such as preferences, personality and social-science outcomes.

“One major impetus for the formation of the SSGAC was the growing recognition that most effects of individual genetic markers on behavioral traits are very small and that, consequently, very large samples are required to accurately detect them,” said Daniel Benjamin, an associate professor of economics at Cornell and a SSGAC co-founder. “We’re troubled by how current approaches in social-science genetics are not bearing fruit. But once research methods are adopted that are suited to the reality of very small effects, we’re excited about the potentially transformative impact that genetic data could have on the social sciences.”

The SSGAC conducted what is called a genome-wide association study (GWAS) to explore the link between genetic variation and educational attainment – the number of years of schooling completed by an individual and whether he or she graduated college. In a GWAS, researchers test hundreds of thousands of genetic markers for association with some characteristics such as a disease, trait or life outcome.

Because the sample included people from different countries – across which schooling systems vary significantly – the research team adopted the International Standard Classification of Education scale, which is a commonly used method for establishing a uniform measure of educational attainment across cohorts.

Anticipating that very large samples would be required to credibly detect genetic associations, the SSGAC researchers assembled a total sample size more than 10 times larger than any previous genetic study of any social-scientific outcome. The team examined associations between educational attainment and genetic variants called single-nucleotide polymorphisms, or SNPs, which are tiny changes at a single location in a person’s genetic code.

The study found that the genetic markers with the strongest effects on educational attainment could each only explain two one-hundredths of a percentage point (0.02 percent). To put that figure into perspective, it is known from earlier research that the SNP with the largest effect on human height accounts for about 0.40 percent of the variation.

Combining the 2 million examined SNPs, the SSGAC researchers were able to explain about 2 percent of the variation in educational attainment across individuals, and they anticipate that this figure will rise as larger samples become available. The researchers hope that their findings will eventually be useful for understanding biological processes underlying learning, memory, reading disabilities and cognitive decline in the elderly.

The researchers were careful to note that they have not discovered “the gene for education” or that these findings somehow imply that a person’s educational attainment is determined at birth.

“For most social science outcomes such as education, genes probably matter through environmental channels that policy can influence,” Benjamin explained. “Now that we have identified some specific genetic variants associated with educational attainment, we have a starting point for exploring how their effects are dampened or amplified by other factors, such as public policy, parental behavior and economic status. Such research may eventually shed light on which policies might work best for improving educational outcomes.”

The study, “GWAS of 126,559 individuals identifies genetic variants associated with educational attainment,” was supported by a number of funding agencies, including the National Institute on Aging/National Institutes of Health, the National Science Foundation and the Söderbergh Foundation.