In summary, the presence of an additional X chromosome in males has significant effects on both brain structure and function, in at least a subset of individuals. Several brain regions appear to be affected, with differences in frontal and temporal lobe structures reported by several of the existing studies using different patient groups and methods, and some suggestion of relative preservation of parietal regions. Microstructural white matter abnormalities are suggested by decreased FA and a high prevalence of white matter hyperintensities. Although the evidence of significant abnormalities in structural asymmetry is equivocal, both SPECT and fMRI functional imaging studies found decreased lateralization in 47,XXY subjects compared with controls, primarily due to increased activity in the right hemisphere.
