analysis to identify a latent phenotype that reflected genetic covariation (ie, shared genetic susceptibility) across the 6 phenotypes (major depressive disorder, generalized anxiety disorder, panic disorder, agoraphobia, social phobia, and neuroticism [Hettema et al47 provide the details]). The inclusion criterion was the top and bottom 25th percentile of a genetic factor score—a composite index that represented several internalizing anxiety and neuroticism phenotypes.48 The cases had a mean raw neuroticism score of 6.30 (z score=1.04) and had the following frequencies of the target psychiatric illnesses: major depressive disorder (80.1%), generalized anxiety disorder (53.8%), panic disorder (20.5%), agoraphobia (14.1%), and social phobia (17.5%). The controls were free of the 5 disorders and had a mean raw neuroticism score of 0.55 (z score=−0.89). This sample contains 1128 individuals, of whom 6 were included in the VAND sample and another 161 were co-twins of the participants in the VAND. To maintain the independence of the 2 samples, these 167 overlapping individuals were removed from all analyses conducted with the VAANX sample. Because the VAANX was selected by the genetic factor score, there were not enough individuals with high and low FTQ or FTND scores for a dichotomized design, so we used a quantitative design
