A psychometric-genetic study of schizotypal disorder

This study aimed to clarify the structure and the etiological constituents of schizotypal disorder (SPD) by directly interviewing pairs of twins. A la tent class analysis was applied to each individual's outcome for specified SPD items, such that each subject's phenotype could be redefined in terms o f individual probabilities of class membership. Intraclass correlations wer e then calculated for each twin pair, and a standard univariate twin model applied. The best latent class analysis solution encompassed a model with f our latent classes (three latent classes of SPD subjects, one of non-SPD). The intraclass correlations revealed a moderate to high heritability for tw o out of three SPD classes and for the modal class (a class composed of sub jects that possessed a conditional probability of belonging to any of the S PD classes). Model fittings revealed considerable variation in the extent t o which the different classes of SPD were influenced by additive genetic co nstituents or non-genetic factors. Although these data confirm the importan ce of genetic contributors in determining liability to SPD and the schizoph renia spectrum, they indicate that there is a relationship between psychome tric multidimensionality and etiological heterogeneity in SPD. (C) 1999 Pub lished by Elsevier Science B.V. All rights reserved.