Most cases of sex chromosomal abnormalities in humans have a case of learning disability or less developed cognitive abilities. Wikipedia says:
When additional X and/or Y chromosomes are present in 48,XXXY, 48,XXYY, or 49,XXXXY, developmental delays and cognitive difficulties can be more severe and mild intellectual disability may be present
So, the question is simply this: How is cognitive ability linked to the presence of sex chromosomes?