Does the Schizotypal Personality Questionnaire reflect the biological–genetic vulnerability to schizophrenia?

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Abstract

We investigated whether the Schizotypal Personality Questionnaire (SPQ) [Schizophr. Bull. 17 (1991) 555.] could be an indicator of the biological–genetic vulnerability to schizophrenia. We hypothesized that the mean scores on three dimensions of the SPQ of different groups of relatives of patients with schizophrenia would parallel their risk for developing schizophrenia. The SPQ was administered to 51 first-episode schizophrenia patients, 63 parents of schizophrenia patients, 42 siblings of schizophrenia patients and 12 children of schizophrenia patients. Patients differed from the relatives on all three dimensions. Siblings and children scored significantly higher than parents on Positive Schizotypy, and the insignificant difference between the siblings and children was in the expected direction. The results could not be explained by the differences in age, sex, IQ or substance abuse. No differences were found for Disorganization Schizotypy between the relatives. Children scored higher than parents on Negative Schizotypy. The current study offers support to the hypothesis that the positive dimension of SPQ reflects the genetic vulnerability to schizophrenia.

Introduction

Recently, Tsuang et al. (1999) showed that schizotypal personality traits are found to a much higher degree in first-degree relatives of schizophrenia patients than in normal controls. They concluded that the prevalence rate for the schizotypal personality disorder in first-degree relatives was about 15% and that even a higher rate of subclinical schizotypal traits is to be expected in these relatives. Studies by Kety et al. (1994), Tsuang et al. (1991) and Kendler et al. (1995) consistently found these high rates of schizotypal traits among the biological relatives of schizophrenia patients. These studies mainly using interviews predominantly reported negative symptom-like features among relatives. Tsuang et al. (1999) argued that higher rates of schizotypal traits in relatives reflect the biological–genetic vulnerability to schizophrenia. The construct of (questionnaire) schizotypy is comprised of three dimensions (Venables, 1995). Recent factor analytical studies showed that questionnaire items of schizotypal traits can be reduced to three latent variables, viz. the positive, negative and disorganization dimensions of schizotypy Raine et al., 1994, Vollema and Hoijtink, 2000 (see Table 1). These findings qualify the Schizotypal Personality Questionnaire (SPQ) as a sound psychometric and multidimensional questionnaire for assessing schizotypal traits, and therefore, as a promising indicator of the genetic vulnerability to schizophrenia. Although many studies investigated the occurrence of schizotypal traits in relatives, a small minority used the questionnaire approach. Kendler et al. (1996) used interviews and questionnaires in a family study and concluded that interviews discriminate relatives from controls better than questionnaires. Kremen et al. (1998) compared SPQ scores of normal controls to the scores of the biological relatives of schizophrenia patients. Relatives scored higher on Positive Schizotypy than the controls. No differences were found for the Negative and Disorganization Schizotypy dimensions. Since previous studies showed that negative symptom-like features occurred more frequently among relatives, the findings of Kremen et al. (1998) on Positive Schizotypy were unexpected. However, Yaralian et al. (2000) replicated the findings of Kremen, viz. Positive Schizotypy scores were elevated in relatives as compared to controls. These findings offer support for the hypothesis that the SPQ, as far as the positive dimension is concerned, reflects the genetic vulnerability to schizophrenia.

The discrepancy in the results between the recent and older studies may be due to instrument variation (Yaralian et al., 2000). For instance, Kendler et al. (1996) used the Magical Ideation Scale (MIS; Eckblad and Chapman, 1983) to assess Positive Schizotypy and the Social Anhedonia Scale (SAS; Chapman et al., 1976) to assess Negative Schizotypy. The SAS identified the relatives of the schizophrenia patients but the MIS did not. The Perceptual Aberration Scale (PAS; Chapman et al., 1978) and the MIS as well have overt psychotic-like items and contrasts with the SPQ on this point. Due to their overt psychotic-like contents, the PAS and MIS may be more vulnerable to a defensive response set of the relatives as compared to the SPQ.

Further evidence for the hypothesis that Positive Schizotypy, as assessed with the SPQ, reflects the genetic vulnerability to schizophrenia may come from studies investigating SPQ scores of various kinds of relatives. Gottesman (1991) presented the lifetime risks of developing schizophrenia for various kinds of relatives. He compiled these risks from many family studies and concluded, with respect to first-degree relatives, that the risk for parents is 6%, for siblings 9% and for children 13%.

The aim of the present study was to evaluate the SPQ as an indicator of the genetic vulnerability to schizophrenia. If the SPQ reflects this genetic vulnerability, then scores of various kinds of relatives should parallel the risk percentages as presented by Gottesman. SPQ scores should be highest for patients than for the children of patients, followed by the siblings and parents of schizophrenia patients, respectively.

Section snippets

Subjects

The sample of our study consisted of 168 subjects (see Table 2). Fifty-one patients with first-episode schizophrenia or schizophreniform disorder, according to DSM-IV, participated in the study. Diagnoses were based on the Comprehensive Assessment of Symptoms and History (CASH; Andreasen et al., 1992). Subjects were physically healthy, had no history of neurological or medical illness (based on medical checklist and medical records) and had no premorbid IQ below 85 (based on the Dutch National

Discussion

We examined the validity of the SPQ as an indicator of the genetic vulnerability to schizophrenia. We hypothesized that the mean SPQ scores of different groups of relatives would parallel the risk of these groups for developing schizophrenia.

The main findings with respect to the three dimensions of the SPQ were as follows. Significant differences were found for Positive Schizotypy: (1) schizophrenia patients scored higher than all groups of relatives, (2) children of schizophrenia patients

Uncited references

American Psychiatric Association, 1994

Acknowledgements

We would like to thank Mrs. Belinda Postma for her assistance in scoring and Mrs. Mechteld Hoogendoorn for her assistance in the collection of the SPQ data.

References (23)

  • W.S. Kremen et al.

    Sex differences in self-reported schizotypal traits in relatives of schizophrenic probands

    Schizophr. Res.

    (1998)
  • P.S. Yaralian et al.

    Elevated levels of cognitive–perceptual deficits in individuals with a family history of schizophrenia spectrum disorders

    Schizophr. Res.

    (2000)
  • Diagnostic and Statistical Manual of Mental Disorders

    (1994)
  • N.C. Andreasen et al.

    The comprehensive assessment of symptoms and history (CASH): an instrument for assessing psychopathology and diagnosis

    Arch. Gen. Psychiatry

    (1992)
  • L.J. Chapman et al.

    Scales for physical and social anhedonia

    J. Abnorm. Psychol.

    (1976)
  • L.J. Chapman et al.

    Body image aberration in schizophrenia

    J. Abnorm. Psychol.

    (1978)
  • B.A. Clementz et al.

    Psychometric detection of schizotypy: perceptual aberration and physical anhedonia in relatives of schizophrenics

    J. Abnorm. Psychol.

    (1991)
  • M.L. Eckblad et al.

    Magical ideation as an indicator of schizotypy

    J. Cons. Clin. Psychol.

    (1983)
  • I.I. Gottesman

    Schizophrenia Genesis: The Origins of Madness

    (1991)
  • K.S. Kendler et al.

    Schizotypal symptoms and signs in the Roscommon family study

    Arch. Gen. Psychiatry

    (1995)
  • K.S. Kendler et al.

    Self-report measures of schizotypy as indices of familial vulnerability to schizophrenia

    Schizophr. Bull.

    (1996)
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