Relatedness of schizotypal personality to schizophrenic disorders: multifactorial threshold model

Genetic analysis of schizophrenia and schizotypal personality disorder (SPD) was conducted on two pedigree samples. The results are interpreted in terms of a multifactorial threshold (MFT) model. A high rate of schizophrenia was found in relatives of both samples, but any excess of SPD was found only in relatives of the SPD sample. Based on these data, the hypotheses assuming a single liability with two thresholds (Reich's model) and different liability (Smith's model) for both disorders were rejected. The coefficient of genetic correlation is 0.61. Our data suggest that schizophrenia and SPD are separate nosological entities and that some of the factors which constitute liability to SPD influence the development of schizophrenia, but not vice versa.