DNA was isolated from whole blood or saliva using the Puregene kit and its protocols (Qiagen, Venlo, Netherlands). Polymerase chain reaction and agarose gel electrophoresis were used to determine the length as previously described (Sen, Burmeister, & Ghosh, 2004a). Genotypes SS, LS, and LL were in Hardy Weinberg equilibrium. Based on prior evidence that the L allele is recessive (Hariri et al., 2002; Heinz et al., 2000), we used a dominant model and thus compared the LL genotype to S carriers (LS/SS). Among European-Americans, the frequency of the S allele is 0.43 (Odgerel, Talati, Hamilton, Levinson, & Weissman, 2013).
