Neurocognitive, behavioural and neurodevelopmental correlates of schizotypy clusters in adolescents from the general population

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Abstract

Introduction: Studies on the neurocognitive correlates of schizotypy dimensions have found inconsistent results. This might stem from the fact that correlational methods, in contrast to cluster analysis, do not account for the possibility that a subject presents high scores on more than one dimension simultaneously. We aimed to establish clusters of normal adolescents based on schizotypy dimensions and compare them on neurocognitive, behavioural, and neurodevelopmental markers. Methods: Two hundred seventy normal adolescents from the general population (mean age 13.4, SD=0.72) attending obligatory education were evaluated. Results: A K-means iterative cluster analysis was performed with the Perceptual Aberration, Revised Social Anhedonia and Physical Anhedonia Scales. A forced four-cluster model yielded the following clusters: ‘negative schizotypy’, ‘high or mixed schizotypy’, ‘positive schizotypy’, and ‘normal scorers’. Comparisons with ANOVAs showed that ‘high schizotypes’ performed poorly on neurocognition (Wechsler Intelligence Scales for Children-Revised (WISC-R) and Verbal Fluency (FAS)) and obtained the highest teacher ratings (TRF) of behavioural problems. ‘Negative schizotypes’ had the worst WCST results and more dermatoglyphic abnormalities. Both clusters had more neurological soft signs than ‘normal scorers’ and ‘positive schizotypes’. Conclusions: Our results with community adolescents found the same cluster structure than the previous cluster analytic studies conducted in adult college subjects. Furthermore, we showed differences among them on neurocognitive and malneurodevelopment markers consistent with the adult literature on schizotypy.

Introduction

The dimensional approach to schizophrenia has shown that the psychotic phenotype can be described as the simultaneous variation of distinct but correlated symptom dimensions (Stefanis et al., 2002), such as the positive, negative, and disorganisation dimensions Bilder et al., 1985, Liddle, 1987, Peralta et al., 1992. In turn, schizotypy has been shown to have a highly similar dimensional structure in the general population, with factors resembling the positive, negative, and cognitive disorganisation dimensions Raine et al., 1994, Claridge et al., 1996, Vollema and Van den Bosch, 1995.

It has been claimed that the heterogeneity of neurocognitive performance in schizophrenia/schizotypy may be explained by the predominant profile of symptom/trait dimensions. This hypothesis has produced a large but inconsistent bulk of studies, in which all dimensions have been more or less specifically associated with attention, memory, and executive dysfunctions (e.g., Strauss, 1993, Elliott and Sahakian, 1995).

These inconsistencies might stem from the fact that correlational methods, in contrast to cluster analysis, do not account for the possibility that a subject presents high scores on more than one dimension simultaneously (Walker and Lewine, 1988). Indeed, factor analyses are based on the interrelationships between measures and therefore cannot inform us about how subjects might be grouped according to their responses on those measures.

However, there have been much less cluster than factor analytic studies in both schizophrenia and schizotypy. Recently, Suhr and Spitznagel, 2001a, Suhr and Spitznagel, 2001b reviewed this sparce literature and conducted a series of cluster analytic studies of schizotypy in college students. They forced the analysis to four clusters since previous cluster analytic studies in both schizophrenia van der Does et al., 1993, Williams, 1996 and schizotypy Williams, 1994, Williams, 1995, Loughland and Williams, 1997 had consistently found four distinctive clusters. They analysed a large sample of normal undergraduate students (Suhr and Spitznagel, 2001a) and found one cluster high in both positive and disorganised features and three clusters with mixed features of varying levels of severity. In two further analyses, one with a subsample of high scorers on schizotypy (Suhr and Spitznagel, 2001a) and another one with a mixed sample of highly schizotypic subjects and normal controls (Suhr and Spitznagel, 2001b), they found three groups of schizotypals (predominantly negative schizotypy, predominantly positive schizotypy, and high on all dimensions) and a group of normal controls. They compared these latter clusters on neurocognitive measures and found that the cluster with predominantly negative schizotypy performed worse than all the remaining clusters on the Wisconsin Card Sorting Test (Suhr and Spitznagel, 2001b). However, the cluster of subjects high on both negative and positive schizotypy was rated as having the most unusual social behaviour by naı̈ve raters.

The results of these kinds of studies, showing that similar clusters of symptoms and traits are found in schizophrenic and normal populations and that they also have similar neurocognitive profiles, lend support to the notion of a continuum from normal personality variation to psychosis Crow et al., 1995, Claridge, 1997, van Os et al., 1999. An interesting extension of these studies would be to establish whether subjects displaying certain schizotypic profiles also exhibit a higher number of risk factors that are supposed to have an etiopathogenic value for schizophrenia. Given that one of the most relevant etiological hypotheses of schizophrenia is that of an abnormal neural development Murray and Lewis, 1987, Weinberger, 1987, markers of malneurodevelopment such as the presence of neurological soft signs, dermatoglyphic abnormalities, or minor physical anomalies, may be of great interest in this research context.

Our aims were twofold. First, we attempted to replicate the study by Suhr and Spitznagel (2001b) in a representative community adolescent sample; to that end, we established clusters of subjects according to their schizotypal profile and compared them on neurocognitive and behavioural measures. Secondly, we included some biological measures that inform us about malneurodevelopment, in order to discover whether the schizotypy-based clusters share some of the hypothesized etiopathogenic mechanisms assumed for schizophrenia. Based on the previous cluster analytic studies by Suhr and Spitznagel (2001b) and Williams (1994), we predicted that there would be a cluster with predominantly positive schizotypic traits and a cluster with negative traits, as well as a cluster of subjects with average or low schizotypy scores. Concerning the neurocognitive measures, and again departing from Suhr and Spitznagel's (2001b) results, we predicted that the cluster with high negative schizotypy would show a poorer performance than the other clusters. Finally, given that the negative symptom dimension has been shown to be more strongly associated with markers of neurodevelopmental deviance Murray et al., 1992, van Os et al., 1998, we predicted that the cluster of negative schizotypy would present with a higher rate of neurodevelopmental abnormalities.

Section snippets

Subjects

The sample analysed in this study consisted of 270 (141 boys, 129 girls) normal adolescents (mean age=13.43; SD=0.72) randomly selected by clusters from the educational centre census of Barcelona. They were attending the last year of primary education in both public and private schools, so there were no biases in terms of educational level.

Measures

We evaluated positive schizotypy with Chapman et al.'s (1978) Perceptual Aberration Scale, and negative schizotypy with the Revised Physical Anhedonia Scale

Cluster analysis

We performed a K-means iterative cluster analysis with the three schizotypy scales. Following the previous existing cluster studies in schizotypy Williams, 1994, Williams, 1995, Loughland and Williams, 1997, Suhr and Spitznagel, 2001a, Suhr and Spitznagel, 2001b, we forced a four-cluster model. We then carried out a multivariate analysis of variance (MANOVA) using the cluster assignment as the independent variable and the schizotypy scores as the dependent variables, in order to obtain a

Discussion

Our clusters resembled very closely Suhr and Spitznagel's (2001b) four-cluster solution in a mixed sample of high schizotypy scorers and normal controls: low on all scales, positive schizotypy, high on both positive and negative, negative schizotypy. As they noted, this pattern of clusters was similar to that found in cluster analyses with schizophrenic samples van der Does et al., 1993, Williams, 1996. Also, there is a great overlap with Williams' (1994) results with an undergraduate sample,

Acknowledgements

Neus Barrantes-Vidal, PhD, thanks the Comissionat per a Universitats i Recerca de la Generalitat de Catalunya for a pre-doctoral grant (1997FI 00427) that made possible this study. This project was funded by the Spanish government (DGICYT PM92-0069).

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