For 5HTTLPR, the genotype frequencies were 19%, 49%, and 32% for SS, SL, and LL, respectively of 5HTTLPR, and for rs25531 these were 86% and 14% for LaLa and LaLg, respectively. The genotypes were combined as five two-locus genotypes: SS, SLg, SLa, LgLa, and LaLa, after removing Sg genotypes [Wray et al., 2009]. Based on the relative frequencies of SLg (6%) and SLa (43%) we estimate that only 0.9% of the total sample are expected to have genotype LgLg or 12% of those genotyped as LgLa. As the rare Lg alleles are functionally equivalent to S alleles [Hu et al., 2006; Wendland et al., 2006], we constructed a 5HTTLPR + rs25531 variable (N = 4,886) with three levels, (1) SS and SLg (25%), (2) SLa and LgLa (51%), and (3) LaLa (24%).
