Zones 1 and 8 are those in which the association is large and positive for one group and large and negative for the other—in other words, cases that support the differential susceptibility model. As with our conclusion from the GWGEI models with the simulated environmental moderator, we find only one SNP in zone 1 and none in zone 8, which provides very little support for the differential susceptibility model when the full distribution of the SNPs is considered. In other words, although rs4358837 demonstrated a slope of –2.2 (p < .01) for non–college graduates and 2.4 (p < .0003) for college graduates (GWGEI p value 1.98E-05), it is clear from the figure that these crossovers are not the norm across the genome (the same conclusion that was drawn from the GWGEI estimates shown in Fig. 2). This SNP is in an intronic region of CYP7B1, which has been linked to cholesterol and drug metabolism (Tsaousidou et al. 2008); again, though, except for this one SNP, the overwhelming bulk of the interesting statistical associations for each group do not demonstrate any evidence of crossover effects that would support the differential susceptibility model.
