Psychological Medicine, Page 1 of 17. doi:10.1017/S0033291714002086

REVIEW ARTICLE

© Cambridge University Press 2014

Childhood trauma and schizotypy: a systematic literature review T. Velikonja1*, H. L. Fisher2, O. Mason3 and S. Johnson1 1

Mental Health Sciences Unit, University College London, UK MRC Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, King’s College London, UK 3 Department of Clinical Psychology, University College London, UK 2

Background. Schizotypy is a complex concept, commonly defined as a genetic vulnerability to schizophrenia that falls on a continuum between healthy variation and severe mental illness. There is a growing body of evidence supporting an association between childhood trauma and increased psychotic experiences and disorders. However, the evidence as to whether there is a similar association with schizotypy has yet to be systematically synthesized and assessed. Method. We conducted a systematic search of published articles on the association between childhood trauma and schizotypy in four major databases. The search covered articles from 1806 to 1 March 2013 and resulted in 17 003 articles in total. Twenty-five original research studies met the eligibility criteria and were included in this review. Results. All 25 studies supported the association between at least one type of trauma and schizotypy, with odds ratios (ORs) ranging between 2.01 and 4.15. There was evidence supporting the association for all types of trauma, with no differential effects. However, there was some variability in the quality of the studies, with most using cross-sectional designs. Individuals who reported adverse experiences in childhood scored significantly higher on positive and negative/disorganized schizotypy compared to those who did not report such experiences. Conclusions. All forms of childhood trauma and other stressful events (e.g. bullying) were found to be associated with schizotypy, with especially strong associations with positive schizotypy. However, because of the methodological limitations of several studies and a lack of further exploration of different possible mechanistic pathways underlying this association, more research is required. Received 27 June 2014; Revised 29 July 2014; Accepted 29 July 2014 Key words: Bullying, childhood trauma, psychosis, schizotypy, systematic review.

Introduction Schizotypal personality disorder (SPD) was introduced as a specific personality disorder in DSM-III, to include the subclinical schizophrenia-like symptoms observed in the relatives of patients with schizophrenia (Spitzer et al. 1979). The American Psychiatric Association defined (DSM-IV-TR) SPD as a ‘pervasive pattern of social and interpersonal deficits marked by acute discomfort with, and reduced capacity for, close relationships as well as by cognitive or perceptual distortions and eccentricities of behavior, beginning by early adulthood’ (APA, 2000, p. 697). Previous research has shown the importance of studying SPD as it provides insight into prodromal phases of schizophrenia,

* Address for correspondence: T. Velikonja, Mental Health Sciences Unit, University College London, Charles Bell House, 67–73 Riding House Street, London W1W 7EJ, UK. (Email: [email protected])

including the aetiology, neuropathology and treatment of this disorder (Seeber & Cadenhead, 2005). The two distinct approaches to the assessment of schizotypal personality reflect categorical/clinical and dimensional/personality conceptualizations (Raine, 2006). The dimensional approach to schizotypy that complements the categorical assessment (as measured by SCID-II; First et al. 1995) originated from psychosisproneness scales, where physical and social anhedonia are the fundamental features (Chapman et al. 1976). The term schizotypy is a multidimensional concept and rather than implying subsymptomatic psychotic experience, it refers to a range of personality traits putatively placing an individual at greater risk of a psychotic disorder, primarily but not exclusively schizophrenia. For most commentators, these traits, at least in their more extreme manifestations, are taken to be the phenotypic indicators related to a genetic vulnerability to schizophrenia (Meehl, 1962). For some in the Meehlian tradition this is a taxon (schizotaxia), of

2 T. Velikonja et al. which membership confers heightened risk. For others, schizotypy represents an inherited general vulnerability to psychopathology that falls on a continuum between healthy variation and severe mental illness (van Os et al. 2000; Rossi & Daneluzzo, 2002; Verdoux & van Os, 2002; Hanssen et al. 2005). Regardless of whether a taxon or dimensions underpin schizotypal traits, it is indisputable that the majority of schizotypal individuals will never make the transition to psychosis; however, they will exhibit a range of positive, negative and disorganized symptom-like experiences (Cochrane et al. 2010) also found in schizophrenia (Liddle, 1987; Arndt et al. 1991; Raine, 1991; Chen et al. 1997; Fonseca-Pedrero et al. 2009). Therefore, schizotypy is a multidimensional construct and factor-analytical studies of the different schizotypy scales have shown that schizotypy may consist of a two-factor [cognitive/positive (e.g. unusual perceptions, magical thinking, ideas of reference, suspiciousness) and interpersonal/negative symptoms (e.g. restricted affect, lack of close friends) (Crow, 1980)], three-factor [with the addition of disorganized symptoms (e.g. odd/eccentric behaviour, poverty of speech) (Liddle, 1987; Raine et al. 1994; Gruzelier, 1996; Chen et al. 1997; Reynolds et al. 2000; Rossi & Daneluzzo, 2002; Fossati et al. 2003)], four-factor [impulsive non-comformity (Mason, 1995; Vollema & Vandenbosch, 1995; Stefanis et al. 2004a,b)] or even a five-factor structure [including traits such as social anhedonia, unusual beliefs and experiences, social anxiety, mistrust, and eccentricity/oddity (Diduca & Joseph, 1999; Chmielewski & Watson, 2008)]. Nevertheless, these schizotypal traits are also considered to increase the likelihood of transition to clinical psychosis. As suggested, high scoring individuals perform in similar ways to individuals with clinically diagnosed psychosis, displaying neurocognitive, behavioural and social deficits, albeit quantitatively less severe (Berenbaum et al. 2003; Myin-Germeys et al. 2003; Campbell & Morrison, 2007; Laurens et al. 2007). Evidence for this continuum approach to psychosis is gained from many experimental studies in which psychosis-like symptoms (Myin-Germeys et al. 2003; Laurens et al. 2007) are commonly experienced in childhood and adulthood (van Os et al. 2001; Johns et al. 2004). In addition, a genetic relationship between schizotypy and schizophrenia was observed in biological relatives of individuals with schizophrenia who exhibited higher levels of schizotypal traits compared to those without a family history of the disorder (Clementz et al. 1991; Kendler & Walsh, 1995; Vollema et al. 2002). This suggests that SPD can be viewed either as an attenuated form of schizophrenia (its premorbid or prodromal stage) or as the natural extension of

normally distributed individual differences in the general population (Raine, 2006). Besides evidence of phenomenological continuity in form and structure, continuity between clinical and subclinical phenotypes (Vollema & Vandenbosch, 1995; Gruzelier, 1996; Vollema & Hoijtink, 2000; Mata et al. 2003) is also demonstrated by transitions over time (Kwapil, 1998), even over periods longer than 15 years (Chapman et al. 1994; Poulton et al. 2000; Hanssen et al. 2005). There is also evidence of aetiological continuity with familial co-clustering of the clinical and the subclinical (Kendler et al. 1993), sharing of risk genes (MacDonald et al. 2001; Linney et al. 2003; Stefanis et al. 2004a), sharing of other environmental risk factors such as cannabis (van Os et al. 2002; Arseneault et al. 2004; Hanssen et al. 2006) and childhood trauma (Read et al. 2005; Steel et al. 2009; Lovatt et al. 2010), dose–response effects of the early environment (van Os et al. 2001), similar neurocognitive deficits (Dinn et al. 2002; Bergida & Lenzenweger, 2006; Cochrane et al. 2012), and also similar associations with demographic factors, for example sex differences (Roy et al. 2001), age-related reduction in schizotypal traits/psychosis-proneness and the positive association with social disadvantage (Verdoux et al. 1998; Peters et al. 1999; van Os et al. 2000; Johns & van Os, 2001). A growing body of literature also suggests an association between childhood trauma and increased schizotypal traits (Johnson et al. 2001; Berenbaum et al. 2003; Steel et al. 2009; Myin-Germeys et al. 2011). Numerous studies have found that increased childhood trauma is experienced by a greater number of schizotypal individuals in comparison with controls (Berenbaum et al. 2003; Campbell & Morrison, 2007), which could not be accounted for by parental psychopathology alone (genetic vulnerability) (Johnson et al. 1999, 2000, 2001). Schizotypal symptoms were associated with all measures of childhood trauma (physical abuse, emotional abuse, sexual abuse and neglect), with the association between neglect and SPD symptoms being particularly strong and not moderated by gender (Johnson et al. 1999, 2000; Berenbaum et al. 2003). Despite the increasing number of studies exploring the association between childhood trauma and schizotypal traits, a systematic review of this literature has not yet been published. An overall association between childhood trauma and both psychosis-like symptoms and psychotic disorders has been reported (Varese et al. 2012) but it is unclear whether, and how conclusively, this has now been demonstrated for schizotypy. Therefore, we have undertaken a systematic review of the available empirical literature to examine the relationship between different types of childhood trauma (psychological/emotional/physical/sexual abuse,

Childhood trauma and schizotypy 3 physical/emotional neglect, bullying and parental loss or separation) and schizotypal traits in community samples but also in some clinical cases (mainly SPD). Method Search strategy The search was conducted in the databases PsycInfo, PubMed, EMBASE and Web of Science, using two sets of search terms. Only the PsycInfo database offers an option to use Medical Subject Headings (MeSH) terms along with a key word search, which helped to broaden the search further. (MeSH is a controlled vocabulary thesaurus that detects citations, even when authors use different terms for the same concept; see http://nnlm.gov/training/resources/meshtri.pdf.) We used the following sets of key words: 1. trauma* OR maltreat* OR abuse OR advers* OR neglect OR bully* OR victim* OR parental loss OR separat* AND adolescen* OR child* AND 2. schizoty* OR psychos* OR psychotic OR illusion OR hallucination OR delusion OR derealisation OR depersonalisation OR social isolation OR hypersensitivity OR magical ideation OR introversion OR referential thinking OR suspiciousness OR restricted affect The search covered publications from 1806 to 1 March 2013 and resulted in 17 003 articles in total. After transferring the data into Reference Manager and extracting the duplicates, 13 050 articles were identified for the title screening. Title screening yielded 801 potentially relevant articles, which were narrowed down to 311 after further abstract screening. Through the full-text screening of the remaining articles, we identified the 25 studies that are used in our analysis. Inclusion and exclusion criteria For papers to be included they had to meet the following criteria: (a) an original research paper, (b) written in English, (c) use a measure of childhood trauma (either emotional, physical or sexual abuse, neglect or bullying; separation from parents or parental loss, or other traumatic experiences, such as household discord, a life- or an injury-threatening event) for occurrences before the age of 18 years, (d) test whether there is an association with schizotypal traits (any standardized or non-standardized measure, assessing either a single schizotypal trait or multidimensional schizotypy), (e) use general population/community samples and not clinical (psychotic) cases, with the exception of SPD (because of the limited number of non-clinical studies involving schizotypal traits), and (f) include full information on design and measures used in the study to

Fig. 1. Flowchart of studies included in the literature review.

allow completion of a quality assessment tool designed for this analysis (e.g. exclusion of conference abstracts because of limited information). The reasons for excluding articles at each stage are documented in Fig. 1. Quality assessment tool Full criteria and scoring are provided in the online Supplementary material. In brief, the quality indicators assessed included the method of sample selection, the percentage of individuals approached who agreed to participate, the size of the sample, the type of assessment tool used to ascertain a history of childhood trauma and the presence of schizotypal traits, whether different types of trauma were considered separately in the analysis, and whether analyses were adjusted for potentially confounding factors (demographic information and other risk factors such as genetic risk, substance use or depression). Each article was assigned a score of 0, 1 or 2 points for each item with a maximum possible score of 14. All scorings were completed by one researcher. Results Following the inclusion criteria, 25 articles were identified and included in our analysis. Using the quality

4 T. Velikonja et al. assessment tool designed for the purpose of this review, we are only providing full information on the papers that had the highest assigned weight (58 points out of a maximum of 14; Table 1) to focus on the most methodologically robust studies. Details of the other papers can be found in the online Supplementary Table S1. Association between childhood trauma and schizotypal traits We examined the relationship between childhood trauma and schizotypal traits in the 25 studies identified. All of the studies support the association between at least one type of trauma and schizotypal traits. Looking at the relationship between overall trauma and schizotypy, the odds ratios (ORs) ranged between 2.01 (Afifi et al. 2011) and 4.15 (Lentz et al. 2010) when adjusted for gender, age, marital status and income. In the studies where different types of trauma were treated separately, particularly strong associations with schizotypy were observed for physical and sexual abuse and neglect. For physical abuse the ORs ranged between 1.62 (Afifi et al. 2011) and 5.84 (for the trait unusual perceptions) (Steel et al. 2009). For neglect, the ORs ranged between 1.35 (Afifi et al. 2011) and 6.7 (Rossler et al. 2007) and for sexual abuse the range was between 2.05 (Afifi et al. 2011) and 4.15 (Lentz et al. 2010). There was also evidence that a history of bullying was associated with all three factors of schizotypy (interpersonal, disorganized and cognitive-perceptual) (Raine et al. 2011). It is also suggested that not only victimization but also being a perpetrator of bullying is associated with higher psychoticism (with even higher scores when a child is a victim and a bully at the same time) (Mynard & Joseph, 1997); however, as only one study examined this relationship, further research is needed. Emotional abuse remained associated with schizotypy even after adjusting for different types of trauma, with an OR of 1.76 (Afifi et al. 2011). Emotional abuse alone also predicted five out of eight SPD symptoms: ideas of reference, excessive social anxiety, a lack of close friends, unusual perceptual experiences and eccentric behaviour or appearance (Powers et al. 2011). The evidence for a strong association between emotional trauma and schizotypy comes from multiple studies (Gibb et al. 2001; Berenbaum et al. 2003; Battle et al. 2004; Lobbestael et al. 2010). Looking at the schizotypy dimensions independently (positive, negative and disorganized), the data were particularly strong for the positive schizotypal dimension. Individuals who reported childhood trauma were 4.82 times more likely to report positive

schizotypal traits than individuals without such experiences, with abuse (defined as emotional, physical or sexual childhood abuse) showing stronger associations (OR 5.53) than neglect (OR 3.67) (Myin-Germeys et al. 2011). Physical and sexual abuse in particular were also strongly associated with paranoia; for physical abuse the OR was 5.84 (Steel et al. 2009) and for sexual abuse the OR was 4.49 (Steel et al. 2009), with physical abuse also predicting unusual perceptions (Powers et al. 2011). Similarly, looking at positive schizotypy, total trauma (including emotional, physical and sexual abuse and emotional and physical neglect) predicted higher precognition, spiritualism, witchcraft and superstition (Perkins & Allen, 2006) and fantasy proneness (Merckelbach & Jelicic, 2004) and physical and sexual abuse predicted unusual beliefs/experiences (Startup, 1999; Berenbaum et al. 2003). Furthermore, there was evidence for an association between adverse childhood experiences and negative schizotypy, for example the association between physical abuse and social anxiety (Powers et al. 2011). An association was also found for childhood trauma and the disorganized schizotypy dimension, including the trait of eccentric behaviour (Powers et al. 2011), which was observed for bullying (Raine et al. 2011), physical/emotional abuse and physical/emotional neglect (Irwin, 2001). Studies that also examined the severity of traumatic experiences and schizotypal symptomatology reported a dose–response relationship (Berenbaum et al. 2008; Myin-Germeys et al. 2011). Discussion There seems to be a considerable amount of evidence that supports the association between different types of childhood trauma and schizotypal traits, with the strongest evidence coming from the highest quality papers (Rossler et al. 2007; Lobbestael et al. 2010; Afifi et al. 2011). Even though there is some evidence of a differential effect of trauma on schizotypy, with especially strong predictors being emotional abuse (Powers et al. 2011) and neglect (Berenbaum et al. 2003), this remains inconclusive. Some studies have reported no differential effect between trauma types (Afifi et al. 2011) whereas others suggested no association with particular types of trauma after adjusting for all trauma types; for example, no association between emotional abuse and schizotypy (Steel et al. 2009), between sexual abuse and schizotypy for men and women (Berenbaum et al. 2008), and between physical abuse and schizotypy in women only (Berenbaum et al. 2008). Exploring the evidence of age, gender differences and possible mediators that underlie the relationship

Table 1. Summary of studies on childhood trauma and schizotypal traits (ordered by quality score) Sample recruited (age range in years)

Study

Study design

Afifi et al. (2011) (Canada)

Cross-sectional representative population-based study

n = 34 653 NESARC (>20)

Lentz et al. (2010) (USA)

Cross-sectional representative population-based study

n = 34 653 (>20)

Number exposed

Measure of schizotypy

Number with outcome

–

Adverse Childhood Experience Study (see Dube et al. 2003) and CTQ (Bernstein et al. 1994) five-point scale Household dysfunction assessed

Child abuse and/or neglect experienced by 30%; household dysfunction 40%; any childhood trauma 52%

AUDADIS-IV (Grant et al. 2001)

–

For SPD group only: 48.3%

Five childhood events prior to the age of 16 (physical abuse by parent/ caretaker; physical abuse by someone other than a parent, witnessing violence at home, neglect by parent/ caretaker, sexual assault)

In SPD group: physical abuse by parent/caretaker (n = 214, 12.4%); witnessing violence at home (n = 411, 25.1%); neglect by parent/ caretaker (n = 203, 12.0%); sexual assault (n = 328, 20.7%)

DSM-IV diagnoses made using AUDADIS-IV (Grant et al. 2001) Schizophrenia and psychotic episodes by asking participants if they had been previously diagnosed

SPD (n = 1534)

Measure of effect Physical abuse versus no abuse and SPD (OR 1.62, 99% CI 1.28–2.03, p < 0.01) Emotional abuse (OR 1.76, 99% CI 1.35– 2.31, p < 0.01) Sexual abuse (OR 2.05, 99% CI 1.59–2.65, p < 0.01) Physical neglect (OR 1.61, 99% CI 1.26–2.05, p < 0.01) Emotional neglect (OR 1.35, 99% CI 1.05–1.74, p < 0.01) Physical abuse by parent/caretaker versus no abuse and SPD (aOR 4.43, 95% CI 3.64–5.40, p < 0.001) Witnessing violence at home and SPD (aOR 3.10, 95% CI 2.65–3.61, p < 0.001) Neglect by parent/caretaker and SPD (aOR 4.57, 95% CI 3.69–5.67, p < 0.001) Sexual assault and SPD (aOR 4.15, 95% CI 3.94–5.16, p < 0.001)

Quality score 12

12

Childhood trauma and schizotypy 5

Measure of trauma

% Female

Study

Study design

Powers et al. (2011) (USA)

Cross-sectional general population study

Sample recruited (age range in years) n = 541 (518, median = 41)

% Female 59.0%

Measure of trauma

Number exposed

Measure of schizotypy

Number with outcome

Self-report CTQ (Bernstein et al. 1994) Early Trauma Interview (Bremner et al. 2000)

Adult trauma (40.2%) Childhood trauma (29.8%) Childhood and adult trauma (30%)

SNAP (Clark, 1993) self-report 375 true–false items (12 trait scales, three temperament scales, six validity scales, 13 PD scales) The Personality Disorder Diagnostic scales (Trull, 2005)

–

Measure of effect Childhood physical and emotional abuse statistically significantly correlated with SPD (r = 0.15, p < 0.001) Physical abuse correlated with unusual perceptions (r = 0.11, p < 0.01), eccentric behaviour (r = 0.15, p < 0.001) and social anxiety (r = 0.12, p < 0.001) Emotional abuse predicted five of eight SPD symptoms when looking at both childhood trauma measures: ideas of reference, excessive social anxiety, a lack of close friends and confidants, unusual perceptual experiences, and eccentric behaviour or appearance Sexual abuse correlated with eccentric behaviour (r = 0.15, p < 0.001)

Quality score 10

6 T. Velikonja et al.

Table 1 (cont.)

Cross-sectional case-control study

n = 409 (18–61, mean = 33.54, S.D. = 10.65)

64.0%

ITEC (Lobbestael et al. 2006): sexual abuse, physical, emotional abuse, physical neglect, emotional neglect

History of any type of maltreatment: 87%

SCID-I and -II (First et al. 1994, 1997)

n = 250 with Axis II diagnosis

Berenbaum et al. (2008) Study 1 (USA)

Cross-sectional representative sample from general population

n = 1510 (18– 95, mean = 44.2, S.D. = 18.1)

52.1%

Telephone interview Physical abuse before age 18 (seven items used sexual abuse, seven acts emotional abuse, two questions physical neglect before age 12, eight items threatening events), adapted from different instruments

Life-threatening events experienced by 46.7%

Telephone interview SPD: five out of nine subscales of the SPQ (Raine, 1991) (odd beliefs, magical thinking, ideas of reference, unusual perceptual experiences, suspiciousness)

–

SPD and sexual abuse (ρ = 0.19, p < 0.01) SPD and physical abuse (ρ = 0.25, p < 0.01) SPD and emotional abuse (ρ = 0.29, p < 0.01) SPD and emotional neglect (ρ = 0.21, p < 0.01) SPD and physical neglect (ρ = 0.11, p < 0.01) When looking at unique effects for each type of maltreatment, SPD and emotional abuse (β = 0.24, p < 0.01) remained significant Individuals who experienced a life- or an injury-threatening event had higher levels of schizotypy symptoms (men: t684 = 4.41, p < 0.01; women: t750 = 4.79, p < 0.01). Childhood maltreatment independently contributed to the prediction of schizotypal symptoms (for men: β = 0.33, p < 0.01 and for women: β = 0.29, p < 0.01)

10

10

Childhood trauma and schizotypy 7

Lobbestael et al. (2010) (The Netherlands)

Study

Study design

Berenbaum et al. (2008) Study 2 (USA)

Cross-sectional representative sample from general population

Sample recruited (age range in years) n = 303 (18–89, mean = 43.2, S.D. = 17.6)

% Female 53.1%

Measure of trauma

Number exposed

Measure of schizotypy

Number with outcome

Physical abuse: modified version of Self-Report of Childhood Abuse Physical (Widom & Shepard, 1996) Sexual abuse as used in Widom & Morris (1997), Emotional abuse and physical neglect: relevant portion of the CTI (Bernstein et al. 1994) + frequency, age of occurrence and perpetrator

–

Schizotypal, antisocial and borderline PD (Personality Disorder Interview-IV) (Widiger et al. 1995)

–

Measure of effect Levels of schizotypal symptoms were associated with higher levels of childhood maltreatment more in men than women (z = 2.24, p < 0.05) Based on regression analysis only emotional abuse was significantly associated with schizotypy symptoms (β = 0.28, p < 0.01). For men, childhood maltreatment (β = 0.46, p < 0.01) contributed independently to the prediction of schizotypy symptoms; for women, maltreatment (β = 0.19, p < 0.05) and PTSD (β = 0.23, p < 0.01) contributed independently

Quality score 10

8 T. Velikonja et al.

Table 1 (cont.)

Prospective study Representative sample from general population

n = 372 (20/21, follow-up at 23, 28, 30, 35 and 41)

–

Life events list according to the Holmes–Rahe scale (Holmes & Rahe, 1967)

–

SPIKE (Angst et al. 1984) SCL-90-R (Derogatis, 1977), including paranoid ideation and psychoticism

–

Battle et al. (2004) (USA)

Longitudinal case– control study

n = 517 with PD n = 83 with MDD and no PD (18–45)

63.0%

CEQ-R (Zanarini et al. 1989) before age 18

In SPD only: Caretaker’s emotional abuse (n = 45, 54%) Caretaker’s verbal abuse (n = 55, 66%) Caretaker’s physical abuse (n = 40, 48%) Caretaker’s sexual abuse (n = 9, 11%) Any neglect (n = 71, 85%)

PD assessed by SCID-I/P (First et al. 1996)

SPD (n = 84)

Johnson et al. (1999, 2001) (USA)

Longitudinal study

n = 793 mothers and their offspring (in 1975: mean = 5.6, S.D. = 2.8) (in 1983: mean = 13.7, S.D. = 2.7) (in 1985: mean = 16.3, S.D. = 2.8) (in 1991: mean = 22.1, S.D. = 2.7)

Offspring 49.2%

Official data on childhood maltreatment obtained from New York State Central Registry and self-reports (yes/no responses)

n = 31 (4.9%) documented cases exposed to childhood maltreatment n = 58 (9.1%) self-reported childhood maltreatment

DISC-I (Costello et al. 1984), Personality Diagnostic Questionnaire (Hyler et al. 1988)

SPD prevalence among individuals with no abuse is 24 (3.4%) versus verbal abuse 6 (7.7%)

Parental neglect (OR 6.7, 95% CI 2.8–16.3, p < 0.001) Conflict among parent (OR 3.5, 95% CI 1.6–7.9, p = 0.002) Having been punished more severely than other children (OR 3.1, 95% CI 1.3–7.8, p = 0.012) associated with continuously high symptom load/ symptom dimension ‘schizotypal signs’ SPD versus MDD Caretaker’s emotional abuse (χ21 = 15.74, p < 0.001) Caretaker’s verbal abuse (χ21 = 8.26, p < 0.004) Caretaker’s physical abuse (χ21 = 8.62, p < 0.003) Caretaker’s sexual abuse (χ21 = 5.85, p < 0.016) Any neglect (χ21 = 9.76, p < 0.02) Childhood abuse/ neglect and elevated symptom levels of SPD (F1,637 = 26.44, p < 0.005) Adjusted for offspring age, parental education, parental psychiatric disorder, physical abuse, sexual abuse

10

10

10

Childhood trauma and schizotypy 9

Rossler et al. (2007) (Switzerland)

Sample recruited (age range in years)

Study

Study design

Myin-Germeys et al. (2011) (The Netherlands)

Cross-sectional case–control study

Patients (n = 272) (16–55, mean = 28.1, S.D. = 8.2) Controls (n = 227) (16–55, mean = 32.3, S.D. = 11.5)

Anglin et al. (2008) (USA)

Longitudinal study Random sample from general population

n = 776 (T0 mean = 5; T1 mean = 16.3; T2 mean = 33.1)

Measure of trauma

Number exposed

Measure of schizotypy

Number with outcome

Patients 30.6% Controls 69.7%

CTQ (Bernstein et al. 1997)

High trauma (scoring above fourth quartile) In patients n = 155 (57%) In controls n = 61(27%)

Positive and Negative Syndrome Scale and Structured Interview for Schizotypy – revised (Vollema & Ormel, 2000)

–

49.0%

Maternal separation for at least 1 month; reported by mothers

–

Children in the community selfreport SPD symptom scale (Crawford et al. 2005)

–

% Female

Measure of effect Healthy comparison group: Trauma/any versus no trauma and positive schizotypy (OR 4.82, 95% CI 2.04–11.39, p < 0.001) Abuse and positive schizotypy (OR 5.53, 95% CI 2.15–13.29, p < 0.001) Neglect and positive schizotypy (OR 3.67, 95% CI 1.60–8.41, p < 0.001) Separation before age 5 and average SPD symptoms (β = 2.03, S.E. = 1.05, p < 0.05)

Quality score 8

8

NESARC, National Epidemiologic Survey on Alcohol and Related Conditions; AUDADIS-IV, Alcohol Use Disorders and Associated Disabilities Interview Schedule – DSM-IV Version; SPD, schizotypal personality disorder; OR, odds ratio; aOR, adjusted odds ratio; CI, confidence interval; CTQ, Childhood Trauma Questionnaire; SNAP, Schedule for Nonadaptive and Adaptive Personality; PD, personality disorder; ITEC, Interview for Traumatic Events in Childhood; SCID-I and -II, Structured Clinical Interview for DSM-IV Axis I and II Disorders; SCID-I/P, Structured Clinical Interview for DSM-IV Axis I Disorders, Patient Edition; SPQ, Schizotypal Personality Questionnaire; CTI, Childhood Trauma Interview; PTSD, post-traumatic stress disorder; SPIKE, Semi-Structured Psychopathological Interview; SCL-90-R, Symptom Checklist-90-Revised; MDD, major depressive disorder; CEQ-R, Childhood Experiences Questionnaire – Revised; DISC-I, Diagnostic Interview Schedule for Children; S.E., standard error; r, Pearson correlation coefficient; ρ, Spearman’s rank correlation coefficient; β, beta regression coefficient; t, T test; z, Kruskal–Wallis test; χ2, chi-squared test.

10 T. Velikonja et al.

Table 1 (cont.)

Childhood trauma and schizotypy 11 between childhood trauma and schizotypy might help us to understand the aetiology of psychotic symptoms as well as psychotic disorders. Although gender differences have been shown to play an important role in the association between childhood abuse and psychosis (Fisher et al. 2009), including the possibility of different mechanistic pathways leading to psychosis for men and women (Myin-Germeys & Van Os, 2007), this remains less clear for the association between childhood abuse and schizotypy. With the exception of a few studies, there was no evidence of moderation by sex (Lentz et al. 2010; Lobbestael et al. 2010; Myin-Germeys et al. 2011). However, it was reported that, in women, childhood trauma and post-traumatic stress disorder (PTSD) contributed independently to the prediction of schizotypal symptoms whereas in men only childhood trauma, and not PTSD, contributed to the prediction of schizotypal symptoms (Berenbaum et al. 2008). Thus, a partial mediation effect of PTSD on the association between emotional abuse and SPD in women has been postulated to provide a link between childhood abuse and schizotypal symptoms, especially unusual perceptual experiences and eccentric behaviours (Powers et al. 2011). The association between childhood traumatic events and schizotypy in men, however, was significantly moderated by neurodevelopment disturbance (Berenbaum et al. 2008). Thus, as with psychotic-like experiences, these findings suggest that gender-specific mechanisms may underlie the trauma–schizotypy association. Besides gender, similar heterogeneity occurs for age, with one study suggesting the link between neglect and schizotypy for men increasing with age (Berenbaum et al. 2008) whereas another reported a tendency for such traits to decrease with age (Rossler et al. 2007). Further exploration is therefore needed to fully understand the differential effects of types of trauma on more specific schizotypal traits, including the consideration of other adversity-related factors such as age of occurrence, severity and frequency of trauma, and multiple victimization and perpetrators. In addition, combination effects and multiple traumas have not been fully measured. Nevertheless, the few studies that did look into the severity of traumatic experiences have all reported a dose–response effect of traumatic experiences on schizotypal symptomatology (Berenbaum et al. 2008; Myin-Germeys et al. 2011). There is emerging evidence identifying some symptom-specific and exposure-specific underlying mechanisms; for example, neglect was associated with positive and negative schizotypy whereas childhood abuse (emotional, physical and general) was only associated with the positive schizotypy

dimension (Myin-Germeys et al. 2011). These differential effects between abuse and neglect might be explained by the impact each type of trauma has on the developing brain, with neglect being associated with more severe cognitive and psychosocial deficits (Colvert et al. 2008). Similarly, some specificity was apparent for personality dysfunction, where emotional maltreatment was associated with schizotypy in particular, but sexual abuse correlated with more generalized personality dysfunction (Gibb et al. 2001). By contrast, another study reported that physical and sexual abuse was associated with higher levels of paranoia/suspiciousness and unusual perceptual experiences whereas emotional maltreatment in childhood showed no relationship to any of these experiences (Steel et al. 2009). Individuals who experience paranoia and suspiciousness were also more likely to have high negativeself and negative-others beliefs and high levels of anxiety and depression, which lie beneath the mistrust associated with development of paranoid ideation (Freeman et al. 2002). Pathways between traumatic experiences and unusual perceptual experiences are less clear, and are seen as either an artefact of intrusive memories of traumatic events (Morrison, 2001) or the effect of underlying biological vulnerability caused by early trauma (Garety et al. 2001). Furthermore, childhood trauma demonstrated an especially strong association with positive schizotypy. This is consistent with the hypothesis that negative/disorganized symptoms are more associated with alterations in early brain development (Heckers et al. 1999; Rowland et al. 2009) linked to genetic risk (Goldman et al. 2009), whereas positive symptoms are thought to be influenced more by environmental risk factors (self-reported trauma, cannabis exposure, urbanicity). This suggests two parallel pathways to psychosis: the first endogenous pathway determined mainly by biological factors and a second pathway characterized more by environmental influences (Ross et al. 1994; Dominguez et al. 2010). Again, this indicates the complexity of the childhood trauma and schizotypy relationship and supports the idea that genes and environment interact in complex ways to produce dimensionality of schizotypal traits, which stands as further evidence against any single taxon. Methodological issues The studies varied greatly in the age of the participants, the range being from 6 to 95 years, with about half of them using a wide range of ages, from 18 to ≥ 55 years (Lobbestael et al. 2010; Myin-Germeys et al. 2011), whereas others were limited to children and/or adolescents populations (Mynard & Joseph,

12 T. Velikonja et al. 1997; Raine et al. 2011). The different age ranges make it more difficult to compare the findings, especially as certain schizotypal personality traits have been shown to be associated with age. For example, introverted anhedonia is positively correlated with age whereas unusual perceptual experiences show a negative correlation (Rawlings et al. 2001; Mason & Claridge, 2006). In addition, by using younger samples, especially children up to the age of 14, the possibility that participants might still express schizotypal traits in the future could not be fully excluded as they had not yet passed through the crucial period of risk. There was also heterogeneity in the types of trauma used between different studies, with some only including one type of trauma (Raine et al. 2011) and others using trauma in a much broader context (including, for example, any life-threatening event, conflict among parents, early interpersonal experiences) (Berry et al. 2007; Rossler et al. 2007; Berenbaum et al. 2008). However, the majority of studies did compare different types of childhood trauma (physical, sexual or emotional abuse and neglect), which were also treated separately in the analysis (Lobbestael et al. 2010; Sommer et al. 2010; Afifi et al. 2011; Powers et al. 2011). The definition of childhood trauma differed between studies, with some of them including trauma below the age of 16 only (Lentz et al. 2010); however, most the of studies expanding the age range of trauma occurrence to 18 years (Berenbaum et al. 2008; Afifi et al. 2011). As the majority of studies we included in our review were assessing childhood trauma retrospectively, it is not possible to rule out ‘reverse causality’, that is the possibility that individuals with more schizotypal traits might be more likely to be exposed to violence and trauma. However, the few prospective and longitudinal studies that have been conducted suggest a similar association between childhood trauma and subsequent schizotypy to that demonstrated in crosssectional retrospective studies (Rossler et al. 2007). The vast majority of studies relied on crude measurements of childhood trauma, either a selfadministered checklist or a checklist format completed by an interviewer (Lentz et al. 2010). It is also important to note that some of the studies only used yes/no responses to assess childhood traumatic events, which may result in slightly skewed data (Johnson et al. 1999; Steel et al. 2009). Only one study (Berenbaum et al. 2008) reported on age of occurrence, frequency and perpetrator. Less than one-third of the studies used a semi-structured interview to measure childhood trauma (Berenbaum et al. 2008; Lobbestael et al. 2010) or a medical examination or records from social services (Johnson et al. 1999), which would have provided a better quality of data. Most of the

interviews and questionnaires were based on retrospective reports, which raises the issue of under- or over-reporting and recall bias (McFarland & Buehler, 1998). There is evidence, however, that childhood trauma reports are reasonable reliable and stable over a long period of time even among clinically psychotic patients (Fisher et al. 2011). The studies included in this review ranged from large representative general population studies (Berenbaum et al. 2008; Afifi et al. 2011; Raine et al. 2011) to cohort studies (Sommer et al. 2010; Powers et al. 2011), case–control studies (Simeon et al. 2001; Myin-Germeys et al. 2011) and convenience samples (Perkins & Allen, 2006; Berry et al. 2007; Steel et al. 2009), which again suggests caution when comparing their findings. The sample sizes varied widely from 75 to 34 653 but mainly ranged between 100 and 1000 participants. In addition, 90% of the studies were carried out in the USA or Europe, making it difficult to generalize conclusions to other contexts. When looking at the outcome measure, similar heterogeneity occurs. In some studies schizotypy was measured using standardized measures administrated by clinicians (Afifi et al. 2011; Myin-Germeys et al. 2011), although some individual schizotypal traits were assessed by non-standardized methods and selfreports (Rossler et al. 2007; Powers et al. 2011), and in some cases only a few questions were used. Therefore, this review incorporates the broad range of measures to assess these traits in the general population studies (Berenbaum et al. 2008; Lentz et al. 2010) along with personality traits in some clinical cases (individuals with personality disorders) (Battle et al. 2004), although this also adversely impacts on the ability to compare the findings from the different papers. It is also not possible to fully exclude the potentially confounding effect of other factors when looking at trauma–schizotypy relationships. Studies have mainly adjusted for general sociodemographic factors, with only two studies adjusting for other risk factors such as psychiatric family history, depression and anxiety (Berenbaum et al. 2008; Steel et al. 2009), following which the childhood trauma and schizotypy association remained similarly strong. Future research/clinical implications Building on methodological limitations of previous studies, further exploration of this complex relationship between childhood trauma and schizotypy and the mechanistic pathways underlying this association would potentially help to uncover important clues regarding the aetiology of psychotic symptoms and subsequently psychotic disorders. Focusing on schizotypy,

Childhood trauma and schizotypy 13 which provides a framework for detecting fundamental features of liability to psychosis prior to the illness itself, could have important implications for clinical assessment and treatment formulation. Most importantly, childhood trauma is a risk factor for an array of psychopathology later in life (Bechdolf et al. 2010), so early intervention might help to prevent the transition to later mental health problems. Conclusions This literature review suggests that childhood trauma is associated with increased risk of developing schizotypal traits, especially positive schizotypy in a dose–response manner. The strongest and most consistent effect is shown for emotional abuse; however, there are discrepancies with regard to the differential effects of trauma types on the development of schizotypal traits. Because of methodological limitations, including heterogeneous samples and use of inconsistent measures of trauma and schizotypy, it is difficult to compare findings robustly between the studies included in this review. However, all of the studies did report an association between at least one type of trauma and schizotypal traits. There is also emerging evidence that points to symptom- and exposure-specific underlying mechanisms that support the childhood trauma–schizotypy association, although this issue still requires detailed exploration in future research. Supplementary material For supplementary material accompanying this paper visit http://dx.doi.org/10.1017/S0033291714002086. Declaration of Interest None. References Afifi TO, Mather A, Boman J, Fleisher W, Enns MW, MacMillan H, Sareen J (2011). Childhood adversity and personality disorders: results from a nationally representative population-based study. Journal of Psychiatric Research 45, 814–822. APA (2000). Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision. DSM-IV-TR. American Psychiatric Association: Washington, DC. Anglin DM, Cohen PR, Chen H (2008). Duration of early maternal separation and prediction of schizotypal symptoms from early adolescence to midlife. Schizophrenia Research 103, 143–150. Angst J, Dobler-Mikola A, Binder J (1984). The Zurich study – a prospective epidemiological study of depressive,

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