Investigators working to unravel the impact of genetics versus environment on traits such as obesity may also need to consider a new factor: when individuals were born. In an online article published on December 29, 2014 in PNAS, a multi-institutional research team reports finding that the impact of a variant in the FTO (fat mass- and obesity-associated) gene that previous research has linked to obesity risk largely depends on birth year, with no correlation between gene variant and obesity in study participants born in earlier years and a far stronger correlation than previously reported for those born in later years. "Looking at participants in the Framingham Heart Study, we found that the correlation between the best-known obesity-associated gene variant and body mass index increased significantly as the year of birth of participants increased," says James Niels Rosenquist, M.D., Ph.D., of the Massachusetts General Hospital (MGH) Department of Psychiatry, lead author of the report. "These results -- to our knowledge the first of their kind -- suggest that this and perhaps other correlations between gene variants and physical traits may vary significantly depending on when individuals were born, even for those born into the same families." The authors note that most studies of interactions between genes and the environment have looked at differences within specific birth cohorts -- groups born during a particular span of years -- which would not account for changes in the larger environment that take place over time.
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