Sex chromosome aneuploidies (SCA) may provide insight into the sex‐chromosome impact on sex differences in psychiatric disorders. In particular, if risk of a disorder tracks with the dosage of X or Y chromosomes, this could suggest a mechanism for observed male‐female differences. As described by Green and colleagues, 46 , 47 sex chromosome number has been associated with a range of behavioral phenotypes, and can provide clues to sex chromosome effects on neurodevelopment. Printzlau and colleagues 48 describe the cognitive, behavioral and neural correlates of sex chromosome aneuploidies. On average, people with sex chromosome aneuploidies have greater prevalence rates of ASD and ADHD, as well as cognitive deficits as measured by full‐scale, verbal and performance IQ. 48 However, brain volume differences are more variable, with some evidence that dosage of the X chromosome is related to reduced brain volume (eg, greater reduction in XXY, XXX and XXYY carriers compared with XY and XX, but no brain volume differences in XO and XYY carriers). 48
