Working Papers
Alemu R, Turley P, Okbay A, Benjamin D. Examining the relative predictive performance of polygenic indexes (PGIs) across diverse ancestral populations. 2023.
Improvement in the predictive power of polygenic indices (PGI, also called PRS) is unbalanced across ancestral groups due to the over-representation of European ancestry individuals in most Genome-wide Association Studies (GWASs). The predictive accuracy of PGI falls by an average of ~37, ~50, and ~78 percent in individuals of South-Asian, East-Asian, and African ancestries, respectively. However, most prior studies focus on a few biological phenotypes, such as blood pressure and hemoglobin levels. This paper examines the loss of predictive accuracy in behavioral traits such as educational attainment, substance use, and neuropsychiatric conditions. Our preliminary results show PGI relative accuracy for educational attainment (EA) in African ancestry individuals in the HRS and Add-health cohorts are ~ 11 and 15 percent, respectively. Moreover, we find that the share of predictive accuracy shrinkage attributable to MAF and LD is ~ 65 percent, implying that the remaining loss is likely due to environmental factors or an imperfect cross-population correlation of causal SNPs. Quantifying the relative contribution of these factors may have behavioral, clinical, and policy implications.
Alemu R, Schmitz L. Exposure to higher cigarette taxes during adolescence moderates genetic risk for lifetime smoking behavior. 2023.
Studies on smoking initiation and cessation have recognized the importance of youth smoking on continued smoking in adulthood and have found that differences in statewide cigarette taxation affect the prevalence and intensity of cigarette consumption. This study coupled historical data on state-level cigarette excise taxes with polygenic indices (PGIs) for smoking behavior to assess whether genetically driven changes in lifetime smoking behavior varied by the timing of cigarette tax exposures. Using data from the U.S. Health and Retirement Study, we find that higher cigarette taxes in adolescence were more likely to reduce the probability of lifetime smoking in individuals with higher PGIs for smoking behavior and addiction than cigarette taxes in adulthood. These findings suggest that diminishing price responsiveness to cigarette taxes in the population at large may be temporary as newer generations of high-risk smokers are exposed to progressively higher taxation rates in their youth. Furthermore, we find suggestive evidence that smoking intensity is more sensitive to current taxes, whereas that experienced at younger ages may be more foundational in shaping the probability of lifetime smoking. Overall, the gene-environment interplay that we detect in the present study is consistent with the predictions of the rational addiction model. These findings suggest that prior studies that ignore the timing of cigarette tax exposure and potential gene-environment interaction may have underestimated the true effect of cigarette taxes in encouraging smoking cessation and reducing the risk of developing smoking-related illnesses.
Micronutrients, Child Health and Later-Life Education: Evidence from Wartime Disruption of Iodized Salt in Ethiopia
This study quantifies the impact of iodized salt on child survival and academic achievement based on sudden nationwide changes in access to iodized salt, given naturally occurring geographic variation in iodine. We combine data on birth timing and test scores on national school-leaving exams from 2003 to 2019 with child health surveys and newly collected measures of soil and grain iodine concentrations, finding that children with longer exposure to iodized salt in utero and infancy during the 1990s went on to have lower mortality and higher scores, especially in places with less iodine in locally grown food. Among children with the longest exposure, our main estimates show a national average test score gain of 0.09 standard deviations from widespread iodization, with an additional gain of 0.08 standard deviations for each standard deviation reduction in soil iodine. Placebo tests confirm that effects are specific to iodine (vs. selenium) and specific to cognition and survival (vs. height and weight, which are not affected by iodine deficiency). This provides the first large-scale evidence of how educational achievement is affected by national salt iodization programs recommended by the World Health Organization but not yet universally implemented.
Links:
Preprint Version on Research Square (Under Review at Nature)
Job Market Paper Version (pdf)
Publications
Alemu, R. (2022). The race towards more sustainable food systems. Nature Food, 3(9), 679-680.
Robel Alemu 