Genetic and environmental bases of the interplay between magical ideation and personality

Abstract

Sub-threshold psychotic symptoms are quite commonly present in general population. Among these, Magical Ideation (MI) has been proved to be a valid predictor of psychosis. However, the genetic and environmental influences on the interplay between MI and personality have not fully been explored. A total of 534 adult twins from the population-based Italian Twin Register were assessed for MI using the MI Scale (MIS) and for personality with the temperament and character inventory (TCI). A Multivariate Cholesky model was applied with Mx statistical program. The best-fitting model showed that additive genetic and unshared environmental factors explain approximately the same proportion of variance in MI, whereas a less strong genetic influence on personality traits emerged. Relevant correlations between MI and specific personality traits (novelty seeking, cooperativeness, self-directedness, self-transcendence) were found, suggesting shared influences for MI and these traits. Both genetic and environmental factors explained these correlations, with genetic factors playing a predominant role. Moderate-to-substantial genetic effects on MI and personality were found. Shared genetic and environmental effects underlie the phenotypic correlation between MI (psychosis-proneness) and personality traits, i.e. self-directedness (negative association) and self-transcendence (positive association), potentially representing predictive markers of psychosis liability related to schizotypy and personality.

Introduction

Psychotic-like experiences or sub-threshold psychotic symptoms, such as perceptual aberrations, paranoid ideation or magical thinking are quite commonly experienced by the general population (Fagnani et al., 2011, Fonseca-Pedrero et al., 2011, Nelson et al., 2013), with an average prevalence of 5% in adults (van Os et al., 2009). Epidemiological surveys across specific subgroups of general population such as adolescents, have nonetheless reported different prevalence for some type of attenuated psychotic symptoms, ranging from 8.4% to 44.1% among different studies, as reported by Fonseca-Pedrero et al. (2011). Such psychotic-like experiences have traditionally been associated to schizophrenia-related personality disorders, like schizotypal, paranoid, and schizoid personality disorder (Camisa et al., 2005). In particular, schizotypy, which involves up to 10% of the general population (Nelson et al., 2013), is generally referred to psychosis-liability and attenuated schizophrenia-like traits (Vollema and van den Bosch, 1995). In a phenotypic perspective, schizotypal features include sub-clinical psychotic symptoms like bizarre behavior, magical ideation, social withdrawal/anxiety, lack of feelings, and perceptual abnormalities (Raine, 2006). To a certain extent, it represents a major psychological substrate predisposing to schizophrenia (Fonseca-Pedrero et al., 2011, Nelson et al., 2013) even though only a small group of schizotypal individuals will further develop the disease (Vollema and van den Bosch, 1995). It may therefore be considered as a part of a continuum between psychological health and psychosis vulnerability among the general population (Fonseca-Pedrero et al., 2009).

Over the past few decades, schizotypy has been a matter of major interest primarily for translational implications, such as the implementation of preventive strategies for psychosis (McDonald et al., 2005, Bellani et al., 2010, Correll et al., 2010). Likewise, several conceptualizations on its causative factors have been developed over the past decades. In Meehl's “schizotaxia–schizotypy” model (Meehl, 1962, Kwapil et al., 2008) an ubiquitarious synaptic impairment called hypokrisia, caused by a single major locus (“schizogene”), would underlie specific cerebral abnormalities (“schizotaxia”). This would represent the neural underpinnings of an inherited disposition towards developing psychosis and schizotypal personality traits (Jang et al., 2005). Successively, Tsuang et al. (1999) have revised Meehl's model, defining schizotaxia as the result of the interaction between polygenic and environmental factors (especially pregnancy and neonatal complications) in a complex multifactorial model. These models, differently implying a genetic contribution to schizotypal dimensions and psychosis proneness, have been corroborated by family studies, which revealed that neurological soft signs and cognitive deficits including attention, working memory, and executive functioning are present in first-degree relatives of patients with schizophrenia (Johnson et al., 2003, Solanki et al., 2012), and are associated with schizotypal features (Vollema and Postma, 2002, Johnson et al., 2003). Further evidence of a genetic contribution comes from a number of twin studies (Sullivan et al., 2003, Lataster et al., 2009). Some other twin investigations showed that neuroticism correlates with perceptual and ideational components of schizotypy (Macare et al., 2012) and that the observed relationship between psychotic and personality features is mainly caused by common genetic factors (Jang et al., 2005). In a previous twin study conducted by our group, we showed that genetic factors play a prevalent role in the co-occurrence of psychotic and obsessive traits (Fagnani et al., 2011). Yet, the genetic and environmental influences on the interplay between schizotypal traits and personality in the general population have not been fully elucidated. Specifically, magical ideation is a prominent feature of schizotypal personality and schizophrenia-proneness (Chapman and Chapman, 1980, Chapman and Chapman, 1987, Kwapil et al., 1997). It can be identified as “beliefs in forms of causation that by conventional standards are invalid” and can be assessed by the Magical Ideation Scale (MIS) (Eckblad and Chapman, 1983). For example, it puts in causal relation events that are not actually linked, such as thoughts and external events, or supports strong beliefs in paranormal phenomena. Magical ideation is distributed as a continuum from normal population to schizophrenia and does not pertain to psychosis only (Haslam, 2003). This is in line with dimensional psychopathology, which consider the existence of quantitative and not qualitative differences between normal and psychotic experiences (van Praag et al., 1990, Johns and van Os, 2001, van Os, 2003).

The main objective of this study was to clarify whether genetic effects on magical ideation are independent of higher-order personality traits. Therefore, we used a multivariate twin design to: (i) explore the genetic and environmental architecture of magical ideation and of personality traits in the Italian general population; (ii) investigate the relationship between magical ideation and personality; (iii) unravel the genetic and environmental bases of this relationship.