Although both of these studies are limited by small sample sizes, each found 47,XXX to be associated with significantly decreased overall brain size. Data on whether this was primarily due to gray or white matter differences were not available, although the presence of white matter abnormalities in several of the participants suggests white matter is affected. This would be further supported by a case study of a 6 year female who showed extensive white matter hyperintensities on T2 weighted and FLAIR images [Garcia-Cazorla et al., 2004]. The amygdala did not appear to be as significantly affected by the presence of an additional X chromosome in females compared with males, suggesting that at least part of the reduction in amygdala volumes seen in 47,XXY males is due to the additional influence of an abnormal hormonal milieu.
