Interaction between rs915664 (A) and rs3094212 (B) and its affect on HLA-G expression in the pre-frontal cortex. (a) Summary of the parameters for the interaction model. (b) Histogram displaying the distribution of HLA-G gene expression (normalised to ranks, with a maximum rank of 576, representing the number of individuals in the study) stratified by pairwise genotypic combinations. The individuals with the lowest ranks have the lowest gene expression. The red line denotes the mean rank of the HLA-G expression for each genotype. The mean rank value is denoted xbar. Both main effects, A and B cause an increase in HLA-G expression as seen by the shift in means of HLA-G for genotypes AABB, AaBB, and aaBB and AABB, AABb and AAbb. In the absence of interaction, mean rank HLA-G expression for the aabb genotype is expected to be greater than that for the aaBB and AAbb genotypes. Consistent with the parameterisation of the model, epistasis is visible by the decrease in HLA-G gene expression for the aabb genotype.