Some common patterns in effects from an additional X or Y chromosome are suggested by the available data. The addition of an additional X chromosome in either males or females is associated with a decrease in total brain volume which affects both white and gray matter and becomes progressively more severe with additional supernumerary chromosomes. There appears to be a particularly strong effect in temporal lobe regions, perhaps related to the abnormalities in language development that are frequently found in these individuals. Studies specifically addressing whether the language impairments and increased risk for psychotic symptoms associated with 47,XXY also were associated with differences in brain symmetry did not find strong structural differences, but both SPECT and fMRI studies did observe brain activation to be more symmetrical in the 47,XXY group. This appeared to be due to increased activation in the right hemisphere rather than decrease on the left. Although decreased volume in white matter was not as commonly found as in gray matter, the thinner corpus callosum in 49,XXXXY, decreased FA in 47,XXY, and X-chromosome dosage-related increases in white matter
