To dissect the polygenic architecture of single-episode and recurrent depression, we used dates of diagnosis in the Danish Psychiatric Central Research Register to group the total of 30,618 individuals with depression from the iPSYCH cohort into single episode (N=24,101) and recurrent depression (N=6,517) case groups (see Methods and Supplementary Table S14 for details). We conducted three GWASs: 1) single-episode vs control groups, 2) recurrent depression vs. control groups and 3) recurrent vs. single-episode depression groups (excluding all controls). SNP-heritability estimates were similar for recurrent and single-episode depression and, for the case-only analysis, not significantly different from zero (Supplementary Table S3 and Figure S7). Likewise, the genetic correlations with other phenotypes showed similar patterns for single-episode and recurrent depression (Supplementary Figure S15 and Table S15).
