Another possible contribution to sex bias, beyond the scope of the current study, is the role of sex hormones and chromosomes. There is evidence for a specific role of sex hormones (e.g., estrogen) and sex chromosomes (e.g., X chromosome aneuploidy) in early brain development and neurodevelopmental disorders such as ADHD 28, 50, 51, suggesting that future efforts to examine the role of sex chromosomes and their downstream products in ADHD may be worthwhile. Future studies should also examine the degree of shared genetic risks across ADHD and other developmental conditions (e.g., ASD, ID, congenital abnormalities) in a sex-specific manner as well as the role of rare variants (e.g., CNVs, single nucleotide mutations) in ADHD sex bias.
