These genetic correlations may not generalize to all settings. We observe much weaker genetic correlation of the 23andMe ADHD results with educational attainment, with only partial genetic correlation between 23andMe and the current ADHD GWAS, including significant heterogeneity in the lead chromosome 1 locus. The pattern of replication for the top loci in the deCODE study is stronger but still mixed. These differences may reflect dissimilarities in phenotyping (e.g. self-report vs. medical records), exclusion of individuals with comorbid psychiatric disorders (deCODE), study population (e.g. higher average education and socio-economic status among 23andMe research participants possibly under-representing the proportion of individuals with ADHD with poor educational outcomes in the general population), or other study factors that should be a focus of future work.
