Effect of sex chromosome number variation on attention-deficit/hyperactivity disorder symptoms, executive function, and processing speed.

The sample size for males with Klinefelter syndrome and typically developing males was smaller than the female groups, which may have reduced statistical power to detect differences in the male cohorts. The study did not control for IQ as a covariate in group comparisons due to the small sample size and non-parametric testing choices, so it is unclear if cognitive deficits are solely due to the genetic condition or influenced by overall intellectual ability. Processing speed tests included motor components, so lower scores in Turner syndrome might partly reflect motor difficulties rather than purely cognitive processing speed. The timing of diagnosis for Klinefelter syndrome was limited, and since diagnosis age can correlate with impairment levels, this variable was not fully accounted for. Hormonal differences, particularly in Turner syndrome, may have influenced neurodevelopment, but the study did not isolate these effects.

The authors declared no conflicts of interest. The study was supported by the National Institutes of Health (NIH) and non-U.S. government research support.

Do not assume that all children with sex chromosome aneuploidies present with ADHD symptoms similar to idiopathic ADHD. Turner syndrome is associated with both inattentive and hyperactive-impulsive profiles, while Klinefelter syndrome is primarily associated with inattentive symptoms without significant hyperactivity, which may lead to underdiagnosis if clinicians only screen for hyperactivity.