We present a series of analyses to test the qualitative and quantitative difference hypotheses for the biased sex prevalence in ADHD. First, autosomal common variant data were used to estimate the genetic correlation of ADHD in male and female individuals. We then used population register data to examine whether female individuals with ADHD are at an increased risk for comorbid developmental conditions compared with affected male individuals. Next, genome-wide autosomal SNP data were used to test whether female individuals diagnosed with ADHD carry a higher burden of common risk variants than affected male individuals. Finally, using register data, we tested whether relatives of female individuals with ADHD are at an increased risk for ADHD compared with relatives of diagnosed male individuals.
