Additive Genetic Effects for Schizotypy Support a Fully-Dimensional Model of Psychosis-Proneness

Abstract

Schizotypy is an organization of traits mirroring psychosis-like symptoms and conveying individual psychosis-proneness. Schizotypy and schizophrenia share a genetic basis, wherefore initial schizotypy definitions considered a schizophrenic genotype as a condicio sine qua non. Since the search for a monogenetic schizotypy marker has proven in vain, it is believed that schizotypy is (genetically) based on multiple alleles, each of small effect-size. Schizophrenia may be viewed as a qualitative entity at the extreme of the schizotypy dimension. To date, however, it has not been shown that effects of individual schizotypy-related alleles or genotypes are additive, which would be necessary for the proposition of latent genetic schizotypy factors. Based on previous findings of significant associations of candidate polymorphisms with schizotypy, we chose to examine if these genetic effects were, indeed, additive regarding positive schizotypy. Using a sample of 288 healthy participants we calculated allele-wise and genotype-wise risk indices and examined, whether levels of positive schizotypy would significantly increase with genetic risk. Our findings show significant additive genetic effects of select polymorphisms on positive schizotypy and, thus, support the notion of a fully-dimensional and partially genetically based model of schizotypy.