Genotype distribution was in Hardy-Weinberg equilibrium in the healthy volunteers (χ2=0.38, df=1, p=0.54) and in the depressed subjects (χ2=1.75, df=1, p=0.19). Age (subjects with the L′L′ genotype: mean=37.05 years, SD=13.92; subjects with the L′S′ genotype: mean=38.96, SD=15.96; subjects with the S′S′ genotype: mean=40.61, SD=15.39) (F=0.27, df=2, 64, p=0.76) and sex (χ2=0.87, df=2, p=0.65) did not differ between genotype groups.
Genotype was not associated with diagnosis (χ2=3.71, df=2, p=0.16) (t1). There was no effect of genotype on BP′ and no effect of the interaction of genotype and brain region on BP′ in the healthy comparison subjects (F=0.14, df=2, 39, p=0.87), the subjects with major depressive disorder (F=0.47, df=2, 22, p=0.63), or the two groups combined (F=0.27, df=2, 63, p=0.77). No genotype effects were found in an analysis of the brain regions separately (F1). No difference was found in the cerebellar VT between genotypes (F=0.89, df=2, 65, p=0.42). In analyses in which diagnostic group and genotype were independent variables, there was no main effect of genotype on BP′ (F=0.19, df=2, 58, p=0.83) and no effect of the genotype-by-group interaction on BP′ (F=0.37, df=4, 58, p=0.83). Adding the variables of sex and age to the model did not alter the results.