The genetic correlations of ADHD with other phenotypes were evaluated using LD Score regression42. For a given pair of traits, LD score regession estimates the expected population correlation between the best possible linear SNP-based predictor for each trait, restricting to common SNPs. Such correlation of genetic risk may reflect a combination of colocalization, pleiotropy, shared biological mechanisms, and causal relationships between traits. Correlations were tested for 211 phenotypes with publically available GWAS summary statistics using LD Hub41 (Supplementary Information; see URLs). Additonally, we analysed on our local computer cluster, the genetic correlation of ADHD with eight phenotypes: human intelligence103, four phenotypes related to education and cognition analyzed in samples from the UK_Biobank49 (college/university degree, verbal–numerical reasoning, memory and reaction time), insomnia60, anorexia nervosa44, and major depressive disorder43. The genetic correlation with major depressive disorder was tested using GWAS results from an updated analysis of 130,664 cases with major depressive disorder and 330,470 controls from the Psychiatric Genomics Consortium. As in the previous LD score regression analyses, this estimation was based on summary statistics from the European GWAS meta-analysis, and significant correlations reported are for traits analysed using individuals with European ancestry.
