Vulnerability indicators for schizophrenia refer to anomalous traits that are present prior to, during, and following periods of clinical symptom exacerbations (Nuechterlein and Dawson 1984
; Nuechterlein et al. 1992
). They are presumed to reflect on-going proneness to develop the symptoms of schizophrenia and are thus believed to be more central to core etiological processes than clinical symptoms themselves. The concept of vulnerability factor is closely related to that of an “intermediate endophenotype” (Gottesman and Gould 2003
), although the concept of vulnerability has sometimes been associated with a somewhat broader range of causal factors, including genetic influences as well as neurodevelopmental and other environmental factors (Nuechterlein 1990
). Candidate vulnerability indicators include certain basic neurophysiological and information processing anomalies, as well as subjective experiences or overt behaviors that may be less severe variants of characteristic clinical symptoms of schizophrenia. This report focuses on the latter level of analysis by longitudinally evaluating whether widely used “Psychosis Proneness” scales display the characteristics of vulnerability indicators in recent-onset schizophrenia patients.
Based largely upon Meehl’s (Meehl 1962
) theory of schizotypy, the Chapmans and their colleagues developed five self-report scales to assess a broad range of experiential and behavioral features of schizotypy, a personality organization proposed to reflect vulnerability to schizophrenia or, more generally, psychosis-proneness (Chapman et al. 1995
). The Perceptual Aberration Scale (PerAb) and the Magical Ideation Scale (MagId) measure aspects of positive schizotypy, including distorted perceptions of one’s own body and of other objects, and a tendency to accept unconventional forms of causality. The Revised Social Anhedonia Scale (SocAnh) and the Physical Anhedonia Scale (PhysAnh) assess aspects of negative schizotypy, including diminished experience of pleasure from social and physical stimuli. Finally, the Impulsive Non-Conformity Scale (ImpNon) measures impulsivity and failure to conform to social expectations about the rights of others. These scales have been used in varying degrees across the hypothesized spectrum of schizophrenia-related psychopathology.
The primary use of the Psychosis Proneness Scales has been to identify putatively schizotypal individuals in non-clinical samples. Individuals with elevated scores on the PerAb, MagId, SocAnh, and PhysAnh demonstrate psychological, neurocognitive, and psychophysiological disturbances resembling those of schizophrenia patients, while the presence of such disturbances is less clear in individuals with elevated ImpNon (Edell 1995
; Fernandes and Miller 1995
; Horan et al. 2004
). In the few prospective studies, PerAb and MagId predicted the development of symptoms of psychotic as well as other psychiatric disorders (Chapman et al. 1994
; Gooding et al. 2005
), SocAnh more specifically predicted symptoms of schizophrenia spectrum disorders (Gooding et al. 2005
; Kwapil 1998
), and PhysAnh and ImpNon did not predict later psychosis (Chapman et al. 1994
The status of these scales as vulnerability indictors has been directly evaluated in studies of unaffected biological relatives of schizophrenia patients and, to a very limited extent, in individuals who themselves have schizophrenia spectrum personality disorders (schizotypal, schizoid, and paranoid personality disorders) or schizophrenia. In biological relatives, elevations have most commonly been reported for PhysAnh and SocAnh (Edell 1995
; Horan et al. 2006a
). PerAb and MagId have typically not shown elevations in biological relatives ((Edell 1995
) but see (Lenzenweger and Loranger 1989
)). To our knowledge, no published reports have examined ImpNon in biological family members. The scant research in patients diagnosed with schizophrenia spectrum personality disorders suggests cross-sectional elevations on the Psychosis Proneness Scales ((Camisa et al. 2005
; Thaker et al. 1993
); also see (Bailey et al. 1993
)), though their specificity to these disorders is unclear.
Given the intent of the Psychosis Proneness scales to measure traits associated with vulnerability to schizophrenia, it is somewhat surprising that so few studies have examined them in individuals who are actually diagnosed with schizophrenia spectrum disorders. It is true that these scales were developed primarily for use in non-clinical samples, yet all definitions of vulnerability factors indicate that abnormalities should be present both prior to and following the emergence of clinical symptoms. Thus, if the scales are indeed valid vulnerability indicators, abnormalities should be detectable across time and clinical symptom status in people who meet diagnostic criteria for spectrum disorders.
Nuechterlein and Dawson (Nuechterlein and Dawson 1984
) delineated two criteria for evaluating candidate vulnerability indicators in schizophrenia patients: 1) patients should show abnormality from the general population, and 2) continued abnormality should be present throughout both symptomatic and asymptomatic periods. Studies of these scales in schizophrenia patients have been almost exclusively cross-sectional and therefore address only the first criterion. Patients have repeatedly shown elevated PhysAnh and SocAnh (Horan et al. 2006c
) and less frequently, but consistently, elevated PerAb (Edell 1995
). The remaining scales have been examined much less frequently, though elevated MagId (George and Neufeld 1987
) and ImpNon (Chapman et al. 1984
) have been reported in inpatient samples.
To evaluate the second criterion for a vulnerability indicator, it is essential to study schizophrenia patients longitudinally across different clinical states. To distinguish among indicators that reflect traits, clinical state, or combinations of traits and states, Neuchterlein and Dawson (Nuechterlein and Dawson 1984
) proposed the following tripartite model:
- Stable vulnerability indicators refer to abnormalities that are highly stable and independent of symptom fluctuations. This pattern would be expected for traits that are linked to vulnerability and not directly linked to development of psychotic episodes.
- Mediating vulnerability factors are abnormalities that are present during symptomatic and asymptomatic states, but are more deviant during and possibly somewhat before symptomatic periods. These vulnerability factors are more likely to be involved in subclinical processes leading to formation of clinical symptoms than stable vulnerability indicators.
- Episode indicators, on the other hand, are abnormal during symptomatic periods and normalize in remitting periods, and therefore reflect clinical state rather than enduring characteristics associated with proneness to schizophrenia.
To date, only the PhysAnh and SocAnh have been evaluated longitudinally in schizophrenia patients. During the more chronic stages of the illness, scores on PhysAnh and or SocAnh show good temporal stability across periods of three-months to 20 years (Blanchard et al. 1998
; Herbener and Harrow 2002
; Herbener et al. 2005
) and across acutely symptomatic versus remitted states (in contrast to state-related changes found in depressed patients (Blanchard et al. 2001
)). These findings suggest that anhedonia reflects an enduring trait in schizophrenia, at least among chronically ill patients.
This 15-month study evaluated scores on four Psychosis Proneness scales (PhysAnh, PerAb, MagId, ImpNon) at three time points in recent-onset patients and in healthy controls. The fluctuating early stage of schizophrenia, which includes periods of full remission more frequently than later stages of the illness (Nuechterlein et al. 2006
), provides an excellent opportunity to clarify the extent to which candidate vulnerability indicators represent state or trait phenomena, and minimizes confounds associated with prior treatment or chronicity. Based on the evidence reviewed above, we expected that PhysAnh would demonstrate the characteristics of a stable vulnerability indicator and that ImpNon would reflect an episode indicator. We also expected that PerAb and MagId would demonstrate characteristics of vulnerability indicators, but we did not have strong predictions as to whether they would more likely reflect stable or mediating vulnerability factors.