GWAS was conducted in GWAF (genome-wide association analyses with family) on 12 972 748 SNPs using a linear mixed model incorporating a genetic relationship matrix to control for the relatedness in the family sample.41 Sex and log-transformed age (at the time of EEG recording) were included as covariates in the model, as each of these variables were associated with beta EEG (P<0.001). The first 10 PCs (PC1–PC10) computed from SNPRelate42 were also included as covariates to reduce the risk of false-positives owing to population stratification. An additive genetic model was assumed. Established thresholds for genome-wide significance (P<5 × 10−8) were utilized. Genome-wide complex trait analysis (GCTA) was utilized to determine SNP heritability of fast beta EEG in the analytical sample. The genetic relatedness matrix was incorporated to adjust heritability estimates for familial clustering.
