Despite some success in recent replication efforts involving FTO, there is a lack of evidence for association with BMI in the African-American populations from our study. We genotyped 10 index SNPs located across the FTO region in all six cohorts. We were unable to replicate association at any of these loci, though the direction of association was consistent with previous studies in Europeans (Supplementary Table 4). These negative results may partly be due to a lack of study power. The reported effect size for the A-allele of rs8050136 in Europeans is 0.08 s.d. unit of BMI,17 and given the respective allele frequency of 0.45 in our African-American samples, we would have 98 and 75% power to detect association at α-level of 0.05 and 0.0011, respectively, under an additive model. However, given our sample size, allelefrequency and the effect size in our study of 0.03 s.d. unit of BMI for rs8050136, we had only 32 and 3.6% power to detect association at α-level of 0.05 and 0.0011, respectively. On the other hand, our strongest association observed was for rs9424977 at NEGR1
