In this paper, we have constructed a GRSS comprising 56 common polygenic variants and shown its association with BMI in 2,653 European-Americans and 973 African-Americans from the MGS-C sample. The GRSS was highly associated with BMI (p value = 3.19E−06) and accounted for 0.66% of phenotypic variance in BMI. The association of the GRSS with BMI was comparable to sex, a known factor to influence body composition. The average effect of carrying 10 risk variants was an increase in BMI of 1.1 kg/m2. This corresponds to a weight increase in an average male (5 feet 9 inches, 180 lb) of 8 lb and an average female (5 feet 4 inches, 155 lb) of 7 lb. Further, we have shown the association of the GRSS with BMI was not the result of the few most significant SNPs but rather the aggregate of many SNPs of small effect. These results are consistent with the common disease common variants hypothesis indicating genetic variants common in the population with small effects contribute to the heritability of common traits and diseases.
