MAOA promoter polymorphism alleles and brain structure volumes across diagnostic groups. The figure shows gray and white matter volumes for three cerebral cortex lobes: frontal, temporal, and combined parietal and occipital. Individuals are separated according to diagnostic group: IdASD = idiopathic autism spectrum disorder, FXS-ASD = fragile X syndrome without ASD, and FXS + ASD = fragile X syndrome with ASD. Within diagnostic group, individuals are further stratified by genotype, with diamonds (◊) representing those with high activity and crosses (+) those with low activity MAOA alleles. All values have been adjusted for the covariate of age. Red crosses show least squares means (lsmeans) for each diagnosis-by-genotype group; the horizontal bar is the lsmean and the vertical is the standard error of the mean. For all three diagnostic groups across all six brain regions, the low activity allele is associated with greater volumes than the high activity allele.