We found that the genetic correlation (rG) between minimal and strictly defined MDD included a large proportion of nonspecific liability to mental ill health. The rG between GPpsy (minimally defined MDD) and LifetimeMDD (strictly defined MDD) was 0.81 (s.e. = 0.03), significantly different than unity (Fig. 3c,d, Supplementary Table 15, Supplementary Fig. 6 and Supplementary Note). One interpretation of this finding is that the correlation represents shared genetic liability to MDD4,5. However, the majority of the genetic liability of LifetimeMDD due to GPpsy (approximately rG2 = 0.812 = 66%) was shared with the no-MDD definition, GPNoDep, and the genetic liability of GPNoDep explained approximately 70% of the genetic liability of GPpsy (rG = 0.84, s.e. = 0.05), and 34% of that of LifetimeMDD (rG = 0.58, s.e. = 0.08).
