A different approach to studying sex-specific genetic influences on brain development is to evaluate individuals with sex-chromosomal abnormalities, such as boys with XXY (e.g. Klinefelter syndrome) or 49, XXXXY syndrome, or girls with the commonly studied Turner syndrome (X-monosomy). Individuals with Klinefelter syndrome have reduced gray matter in the insula, temporal gyrus, amygdala, cingulate and hippocampus (Giedd et al. 1996; Patwardhan et al. 2002), while 49, XXXXY boys have smaller total brain size and abnormal development of the white matter with a thinner corpus callosum and multifocal WM lesions (Blumenthal et al. 2013). Brain morphometry studies show that girls with Turner syndrome (TS) have larger volumes of the amygdala and orbitofrontal cortex (Good et al. 2003), as well as larger superior temporal gyrus (Kesler et al. 2003). They also have smaller volumes in parieto-occipital regions and parietal lobes (Murphy et al. 1993; Reiss et al. 1995; Brown et al. 2002; Brown et al. 2004), and reduced FA in parieto-occipital regions along the superior longitudinal fasciculus (Holzapfel et al. 2006). TS girls also have abnormal patterns of brain activation in frontal
