It will be important to test the present etiologic hypothesis at the molecular level. In the present analyses, the genetic influences on each psychopathology dimension were latent, inferred from the analyses of twin pairs. If such participants are genotyped, however, it should be possible to directly estimate A from the measured polymorphisms, although the genotyping and statistical methodologies for doing so are still under development.43 In principle, A for each psychopathology dimension could be estimated from the sums of the varying magnitudes of association of all polymorphisms with that phenotype. The variance-covariance matrix of the A components for all psychopathology dimensions could then be computed and subjected to CFA to determine if the same higher-order factor structure fits the genetic data based on measured polymorphisms.
