These results in aggregate cannot be easily attributed to measurement problems or a lack of heritable variance in this sample. Except for affectively modulated startle, which was neither similar in MZ twins nor appreciably heritable, MZ twin correlations were large for each of the 17 endophenotypes in our special issue, ranging from .53 to .86 (median .66). Table 2 provides the heritability estimates from twin- and family-based models for all endophenotypes. Excluding startle modulation, these ranged from .43 to .85 (median .59). Using GCTA for GREML analysis (Yang et al., 2011), we could show that the endophenotypes were associated with the combined effect of all genotyped SNPs from our GWAS chip, with “SNP heritabilities” (excluding affectively modulated startle) ranging from .04 to .59, median .25 (see Table 2). Hence it was not the case that we arrived at our results because we had no reliable genetic signal to detect.
