Sex versus gender differences in schizophrenia: The case for normal personality differences

Abstract

Schizophrenia has generally been viewed as having a unique preschizophrenia personality or destructive to the personality post-onset. This view is reflected in the scarcity of studies of personality in schizophrenia with the exception of schizotypal personality considered by many as an endophenotype of schizophrenia. What is missing is the study of personality as independent of schizophrenia and as a potential source of schizophrenia heterogeneity. In this study we examine sex versus gender as an initial effort to introduce personality as a normal variant that influences how schizophrenia is expressed. Gender, a personality construct, was associated with the presence of depression in a large sample of schizophrenia patients controlling for sex, age of onset, severity of disorder, and education. The results suggest that gender, rather than sex, as a representative personality trait may yield important insights into how schizophrenia is expressed.

Introduction

As recently pointed out by Silverstein et al. (2014) “… despite thousands of new studies every year, and major technological advances, schizophrenia research is not leading to consistent improvements in the lives of people with the disorder” (p. 259). One of the obstacles identified in trying to advance treatment is within schizophrenia heterogeneity, a phenomenon that has plagued the study, understanding, and treatment of schizophrenia since the time of Kraepelin and Bleuler. Numerous efforts over three decades have been made to understand this variability within schizophrenia; these include the study of sociodemographic characteristics, subtypes, premorbid competence, genetic risk, familial environment, and brain morphology (Corvin et al., 2013, Johnston, 1992, Silveira et al., 2012). We suggest in this study the use of personality differences, using gender as an exemplar and proof of concept, to address some of the variability in the clinical expression in schizophrenia.

The study of personality in schizophrenia has exclusively focused on between-diagnosis comparisons in the pursuit of identifying diagnostic markers, with the assumption that there are shared personality characteristics in schizophrenia (Berenbaum and Fujita, 1994, Ohi et al., 2016). There is a strong bias, introduced by Kraepelin and Bleuler, that the pre-psychosis personalities of schizophrenia patients are different from those with other disorders or healthy individuals. In a meta-analysis of the then-current research, Berenbaum and Fujita (1994) went so far as to ignore the absence of statistical significance in their findings to interpret the data as supporting personality differences in pre-schizophrenia individuals. Current research, while more rigorous in adhering to statistical guidelines, continues to focus on the “unique” personality characteristics of schizophrenia (Ohi et al., 2016).

The study of sex differences in schizophrenia has yielded promising findings, largely in the realm of timing of disorder as a function of neurohormonal processes (e.g. Abel et al., 2010, Goldstein and Lewine, 2000, Salem and Kring, 1998). With rare exceptions, however, “sex” and “gender” have been conflated both in the use of language and in conceptualization. Specifically, although personality may be embedded in the biology of the individual (see Canli, 2006), sex and gender are not the same. It has been more than two decades since Deaux (1993) called for clarification of the two terms. She argued that sex refers to the genetic features that identify man or woman, while gender incorporates aspects of personality, namely more masculine or more feminine, that can apply to either or both of the sexes. The personality framework of gender (semi-independent of sex) is exemplified in the work of Bem and the identification of androgynous, as well as feminine and masculine types across the sexes (Bem, 1994). Importantly, subsets of both men and women were classified as masculine, feminine, and androgynous. With respect to research strategies, Deaux (1993) captured this type of separation between sex and gender in pointing to the differences between “sex comparisons” [woman to man and girl to boy] and “gender comparisons” [gender identification, gender stereotypes, and gender roles]. The two types of comparisons can yield different results and may have different implications, a perspective we explore in understanding schizophrenia.

The purpose of this study was to contrast sex and gender differences in schizophrenia, viewing gender as a personality characteristic. In general, there are multiple confirmed “sex differences”, ranging across biological, psychological, and social domains and include age of onset of the disorder, incidence and prevalence of psychosis, risk factors, symptom expression and outcome (Abel et al., 2010, Falkenburg and Tracy, 2012, Goldstein and Lewine, 2000, Nasser et al., 2002). Briefly, the data suggest that men with schizophrenia have an earlier onset of psychosis, greater social impairments, more negative symptoms, poorer neuropsychological functioning, and poorer outcomes than women with schizophrenia. The focus of this study is the symptomatic expression of affect. Specifically, women are more likely than men to exhibit affect, in particular negative affect such as depression and anxiety, than are men. All of the studies reported in published reviews of sex differences used self-identified sex (woman/man comparisons) as the independent variable, although just as often as not using the term “gender” to refer to the man-woman categorization. In short, none of these studies distinguished between sex and gender, thereby overlooking potential sex, gender (personality), or sex by gender interactions.

As we reported earlier (Lewine, 1991, Lewine, 2004), consideration of sex and gender separately yielded provocative findings in a large sample of schizophrenia patients. Although among those with schizophrenia, women tended to do better than men on tests of neuropsychological functioning, feminine (as measured by the MMPI mf scale) of both sexes performed better than masculine individuals of both sexes. The current study examined the separate impacts of sex and gender on the clinical expression of schizophrenia, with a particular focus on depression for which there is a well-established sex difference. If sex and gender are, indeed, not synonymous with one another, we would expect them to have different relationships with well-established “sex” differences or to account for what appear to be sex differences. A better understanding of personality characteristics (measured as gender in this study), in contrast to sex, could have significant implications for our diagnosis, treatment, and understanding of schizophrenia.