9c
John G. Kerns
I greatly value the comments by Lenzenweger (this volume) and by Le and Cohen (this volume), and I think they add important complementary perspectives to understanding and conceptualizing Cluster A disorders. Professor Lenzenweger discusses Cluster A disorders in the context of previous theory and research on schizotypy and schizophrenia, for instance discussing how schizotypy is a distinct construct from schizotypal personality disorder. Le and Professor Cohen focus on situating Cluster A symptomatology in the context of efforts to move beyond traditional DSM categorical personality disorders as well as efforts to develop alternative assessment methods. I think these are both valuable complementary perspectives to my chapter that was focused primarily on research specifically on DSM Cluster A personality disorder categories. I have some additional comments to offer here in the hope this might further help us understand the nature of Cluster A disorders and symptomatology.
One point made by Professor Lenzenweger with which I strongly agree is that we should not be wedded to a particular methodology to study or conceptualize schizophrenia-spectrum conditions (e.g., his discussion of “psychometric schizotypy”). And as noted by Le and Cohen, new assessment techniques have great potential to help us assess and understand Cluster A disorders. A possibly related tangential comment is that researchers probably should not be constrained by DSM Cluster A disorders in assessing conditions reflective of schizophrenia risk. For instance, negative symptoms in people without schizophrenia do appear to reflect schizophrenia risk, yet the Cluster A disorder that on its surface is thought to be most directly reflective of schizophrenia negative symptoms, schizoid PD, is not strongly related to schizophrenia.
It is interesting to note that schizoid PD is the one Cluster A disorder that has been present in all versions of the DSM. However, given limited research on it, some have argued it should be removed from the DSM (e.g., Triebwasser, Chemerinski, Roussos, & Siever, 2012), further suggesting weaknesses in how well Cluster A disorders capture negative symptoms. Hence research on negative symptoms that potentially indicate increased risk for schizophrenia-spectrum conditions might need to also consider alternative conceptualizations of schizophrenia-spectrum disorders. For instance, Kwapil (1998) found that increased social anhedonia predicts increased risk for Cluster A personality disorders. But given problems with schizoid PD, one wonders if this could be underestimating to what extent social anhedonia predicts clinically relevant schizophrenia-spectrum conditions.
One issue discussed by both of the commentaries is whether Cluster A symptomatology relates to variation in normal personality traits. In this regard, a recent study examined relations between schizophrenia symptoms, schizotypy, and five normal personality traits, with psychoticism, but not openness, included as one of the five normal personality traits (Cicero, Jonas, Li, Perlman, & Kotov, in press). This study of people with psychotic disorders (n = 288) and people without psychosis (n = 257) found that best fitting models included both schizophrenia symptoms and schizotypy on the same factors as normal personality traits. Hence, this provides evidence that not only schizotypy but also schizophrenia symptoms are meaningfully related to normal personality. As noted by Professor Lenzenweger, this in some ways is not a surprising result. Further, this result could be interpreted in multiple ways. At the same time, it is somewhat interesting that models that included separate schizophrenia symptom factors exhibited poorer fit.
Maybe one perspective that could be useful in viewing this research is the idea that Cluster A disorders and schizophrenia, like most forms of psychopathology, might be highly heterogeneous. For instance, one factor in schizophrenia negative symptomatology might be low extraversion. Research focused on testing a low extraversion–negative symptoms link might be a productive line of research. As noted by Le and Cohen, one advantage of such a line of research is that it would benefit from the wealth of existing research on extraversion. But ultimately it would be very surprising to me if a low extraversion explanation would suffice to understand negative symptoms. However, by accounting for the influence of extraversion, and by illustrating aspects of negative symptoms not accounted for extraversion, this research then might help more clearly reveal other non-extraversion negative symptom mechanisms. And again, given heterogeneity, we might expect that any explanation (e.g., negative symptoms reflect low extraversion) to be only a partial explanation.
As noted by Le and Cohen, an RDoC approach might be very valuable in disentangling relations between Cluster A disorders, psychotic disorders, and normal personality. As an example, some positive Cluster A symptoms might lack certain mechanisms critical for schizophrenia (e.g., speculatively, perhaps lacking striatal dopamine dysregulation). However, perhaps these positive Cluster A symptoms might still share some mechanisms in common with schizophrenia. For instance, magical thinking in the general population has been related to cognitive biases (Risen, 2016). One could imagine that these biases on their own might not be sufficient to cause psychotic disorder. On the other hand, cognitive biases have been found to moderate delusion severity in psychotic disorder (Dudley, Taylor, Wickham, & Hutton, 2016). Hence, cognitive biases that contribute to magical thinking in people without psychotic disorder might also be deleterious in people with psychotic disorder. Therefore, an RDoC focus on mechanisms might be very valuable in helping to reveal similarities and differences between Cluster A disorders, psychotic disorders, and normal personality.
References
Cicero, D. C., Jonas, K. G., Li, K., Perlman, G., & Kotov, R. (in press). Common taxonomy of traits and symptoms: Linking schizophrenia symptoms, schizotypy, and normal personality. Schizophrenia Bulletin.
Dudley, R., Taylor, P., Wickham, S., & Hutton P. (2016). Psychosis, delusions and the “jumping to conclusions” reasoning bias: A systematic review and meta-analysis. Schizophrenia Bulletin, 42, 652–665.
Kwapil, T. R. (1998). Social anhedonia as a predictor of the development of schizophrenia-spectrum disorders. Journal of Abnormal Psychology, 107, 558–565.
Risen, J. L. (2016). Believing what we do not believe: Acquiescence to superstitious beliefs and other powerful intuitions. Psychological Review, 123, 182–207.
Triebwasser, J., Chemerinski, E., Roussos, P., & Siever, L. J. (2012). Schizoid personality disorder. Journal of Personality Disorders, 26, 919–926.