Discerning the latent structure of hypothetical psychosis proneness through admixture analysis

Community Psychosis Risk Screening: An Instrument Development Investigation

Schizophrenia and other psychotic disorders are serious psychiatric disorders that are associated with substantial societal, family, and individual costs/distress. Evidence suggests that early intervention can improve prognostic outcomes; therefore, it is essential to accurately identify those at risk for psychosis before full psychotic symptoms emerge. The purpose of our study is to develop a brief, valid screening questionnaire to identify individuals at risk for psychosis in non-clinical populations across 3 large, community catchment areas with diverse populations. This is a needed study, as the current screening tools for at-risk psychotic populations in the US have been validated only in clinical and/or treatment seeking samples, which are not likely to generalize beyond these specialized settings. The specific aims are as follows: (1) to determine norms and prevalence rates of attenuated positive psychotic symptoms across 3 diverse, community catchment areas and (2) to develop a screening questionnaire, inclusive of both symptom-based and risk factor-based questions. Our study will develop an essential screening tool that will identify which individuals have the greatest need of follow-up with structured interviews in both research and clinical settings. Our study has the potential for major contributions to the early detection and prevention of psychotic disorders.

Testing the Validity of Taxonic Schizotypy Using Genetic and Environmental Risk Variables

BACKGROUND

Meehl regarded schizotypy as a categorial liability for schizophrenia that is the product of genes, environment, and gene-environment interactions. We sought to test whether schizophrenia-related genotypes and environmental risk factors predict membership in classes defined by taxometric analyses of positive (cognitive-perceptual), negative (interpersonal), and disorganized schizotypy.

METHODS

Participants (n = 500) completed the Schizotypal Personality Questionnaire (SPQ) and provided information on the following risk factors: cannabis use, pregnancy and obstetric complications, social adjustment, and family history of psychosis. Saliva samples were obtained so that the frequency of single-nucleotide polymorphism (SNP) alleles associated with risk for developing schizophrenia could be determined. Genotyped SNPs were rs1625579 (MIR137), rs7004633 (MMP16), rs7914558 (CNNM2), and rs12966547 (CCDC68). Sets of SPQ items were subject to multiple coherent cut kinetic (CCK) analyses, including mean-above-minus-below-a-cut, maximum covariance, maximum eigenvalue, and latent modes analyses.

RESULTS

CCK analyses indicated latent taxonicity of schizotypy across the 3 item sets. The cognitive-perceptual class had a base rate of 25%, and membership was predicted by the rs7004633 SNP (odds ratio = 2.33, 95% confidence interval = 1.15-4.72 in adjusted analyses). Poor social adjustment predicted memberships in the interpersonal (16%) and disorganized (21%) classes. Classes were found not to be mutually exclusive.

CONCLUSIONS

Schizotypy is taxonic and schizotypy class membership is predicted by genetic and environmental factors that predict schizophrenia. The findings hold the promise that a more complete understanding of schizotypy as a schizophrenia liability state will come from investigation of other genes and environmental factors associated with schizophrenia.

A hierarchical finite mixture model that accommodates zero-inflated counts, non-independence, and heterogeneity

A number of mixture modeling approaches assume both normality and independent observations. However, these two assumptions are at odds with the reality of many data sets, which are often characterized by an abundance of zero-valued or highly skewed observations as well as observations from biologically related (i.e., non-independent) subjects. We present here a finite mixture model with a zero-inflated Poisson regression component that may be applied to both types of data. This flexible approach allows the use of covariates to model both the Poisson mean and rate of zero inflation and can incorporate random effects to accommodate non-independent observations. We demonstrate the utility of this approach by applying these models to a candidate endophenotype for schizophrenia, but the same methods are applicable to other types of data characterized by zero inflation and non-independence.

Evidence of Commingling in Human Eating Behavior

This investigation tested whether distributions of certain aspects of eating behavior were consistent with the notion of a "mixture model;" that is, two or more distinct commingled component distributions, consistent with the possibility of major gene action. Undergraduates (n=901) completed self-report trait measures of hunger, disinhibition, and dietary restraint. Variables were residualized for gender and age and transformed to remove skewness. Residualized transformed distributions were tested for departure from unimodality with Hartigan's dip statistic. The distributions of all three aspects of eating behavior were significantly non-unimodal. Next, component multivariate normal distributions were estimated via maximum likelihood. Likelihood ratio tests were employed to compare nested models. A mixture of four distributions with unequal variance-covariance matrices fit significantly better than any more parsimonious model. In sum, these data strongly suggest that the distributions of several measures of eating behavior are composed of four component distributions. This finding is consistent with the possibility of major gene effects for eating behavior.

A source, a cascade, a schizoid: a heuristic proposal from the Longitudinal Study of Personality Disorders

It is argued that personality pathology represents the final emergent product of a complex interaction of underlying neurobehavioral systems as well as environment inputs. A number of factors may be involved in the developmental pathway and a cascading of effects is plausible, although a unifying cascade for all personality disorders is not likely. The present study suggests a possible cascade relevant to one personality disorder: schizoid personality disorder in emerging adulthood. In brief, it is hypothesized that the absence of a relationship characterized by a rich degree of psychological proximal process in early childhood, which is associated with nurturance and the facilitation of more complex development, predicts impairment in the actualization of the affiliation system (i.e., that system that facilitates interpersonal connectedness and social bonds in human beings and is under substantial genetic influence), and this impairment in the affiliation system predicts the appearance of schizoid personality disorder symptoms in emerging adulthood (late teens/early 20s), which persists over time into emerging adulthood. The impairment in the affiliation system is argued to proceed through childhood sociality as reflected in temperament on through adult personality as reflected in communal positive emotion. Furthermore, it is also hypothesized that the relationship between proximal processes and the affiliation system maintains irrespective of other childhood temperament factors that might adversely impact early parent/caregiver and child relations. The data for a preliminary illustration of this possible cascade are drawn from The Longitudinal Study of Personality Disorders, which is a prospective, multiwave study of personality disorders, personality, and temperament in a large sample of adults drawn from a nonclinical population.

Current status of the scientific study of the personality disorders: an overview of epidemiological, longitudinal, experimental psychopathology, and neurobehavioral perspectives

Research on the nature and development of personality disorders has grown immensely over the past thirty years. A selective summary overview is given of the current status of the scientific study of the personality disorders from several perspectives, including the epidemiological, longitudinal, experimental psychopathology, and neurobehavioral perspectives. From this research, we now know that approximately 10 percent of the general population suffer from a diagnosable personality disorder. Moreover, contrary to nearly a century of theory and clinical pedagogy, modern longitudinal studies clearly suggest that personality disorders decrease in severity over time. The mechanisms by which this change occurs are not understood at present, though it is not likely that change in underlying normal personality systems drives the change in personality disorder. The methods of the experimental psychopathology laboratory, including neuroimaging approaches, are being brought to bear on the nature of personality disorders in efforts to relate neurobiological and neurocognitive functions to personality disorder symptomatology. A model that links personality disorder feature development to underlying, interacting brain-based neurobehavioral systems is reviewed in brief. Current issues and findings illustrative of these developments are given using borderline personality disorder as an exemplar. Finally, areas of intersection between psychoanalytic treatment approaches and the growing science of personality disorder are highlighted.

Sex differences in Wisconsin Schizotypy Scales--a meta-analysis

Previous single studies have found inconsistent results on sex differences in positive schizotypy, women scoring mainly higher than men, whereas in negative schizotypy studies have often found that men score higher than women. However, information on the overall effect is unknown. In this study, meta-analytic methods were used to estimate sex differences in Wisconsin Schizotypy Scales developed to measure schizotypal traits and psychosis proneness. We also studied the effect of the sample characteristics on possible differences. Studies on healthy populations were extensively collected; the required minimum sample size was 50. According to the results, men scored higher on the scales of negative schizotypy, ie, in the Physical Anhedonia Scale (n = 23 studies, effect size, Cohen d = 0.59, z test P < .001) and Social Anhedonia Scale (n = 14, d = 0.44, P < .001). Differences were virtually nonexistent in the measurements of the positive schizotypy, ie, the Magical Ideation Scale (n = 29, d = -0.01, P = .74) and Perceptual Aberration Scale (n = 22, d = -0.08, P = .05). The sex difference was larger in studies with nonstudent and older samples on the Perceptual Aberration Scale (d = -0.19 vs d = -0.03, P < .05). This study was the first one to pool studies on sex differences in these scales. The gender differences in social anhedonia both in nonclinical samples and in schizophrenia may relate to a broader aspect of social and interpersonal deficits. The results should be taken into account in studies using these instruments.

Does change in temperament predict change in schizoid personality disorder? A methodological framework and illustration from the Longitudinal Study of Personality Disorders

Personality disorders (PDs) have been thought historically to be enduring, inflexible, and set in psychological stone relatively firmly; however, empirical findings from recent prospective multiwave longitudinal studies establish otherwise. Nearly all modern longitudinal studies of personality disorder have documented considerable change in PDs over time, suggesting considerable flexibility and plasticity in this realm of psychopathology. The factors and mechanisms of change in the PDs remain essentially opaque, and this area of PD research is just beginning to be probed using candidate predictors of change, such as personality systems. In this report, we investigate whether change in temperament dimensions (emotionality, activity, and sociability) predicts change in schizoid personality disorder. We present a latent growth framework for addressing this question and provide an illustration of the approach using data from the Longitudinal Study of Personality Disorders. Schizoid personality disorder was assessed using two different methodologies (structured psychiatric interview and self-report) and temperament was assessed using a well-known psychometric measure of temperament. All constructs were measured at three time points over a 4-year time period. To analyze these panel data, we fitted a covariance structure model that hypothesized simultaneous relationships between initial levels and rates of change in temperament and initial levels and rates of change in schizoid personality disorder. We found that rates of change in the core temperament dimensions studied do not predict rates of change in schizoid personality over time. We discuss the methodological advantages of the latent growth approach and the substantive meaning of the findings for change in schizoid personality disorder.

Taxonic structure of schizotypal personality in nonclinical subjects: Issues of replicability and age consistency

To assess the replicability and age consistency of the taxonic structure and base-rate of schizotypy, 803 university students (21.9 years) and 929 high school students (16.4 years) were administered three self-report measures of schizotypal personality. The two groups came from the same town and were matched on gender. MAXCOV analyses were consistent with a low base-rate taxon of approximately 10% only in the university student group; in the younger group, the three schizotypal personality measures did not show clear evidence of taxonicity. These findings support the hypothesis of the taxonic structure of schizotypal personality in adult subjects, but they raise questions concerning the identification of schizotypy in younger samples.

Taxonic structure of schizotypal personality disorder: a multiple-instrument, multi-sample study based on mixture models

This study used a multi-sample, multiple-instrument strategy to evaluate the hypothesis that schizotypal personality disorder (SPD) is taxonic. In Study 1, 721 consecutively admitted inpatients and outpatients were evaluated with the Structured Clinical Interview for DSM-IV Axis II Personality Disorders (SCID-II) and the Personality Diagnostic Questionnaire-4+ (PDQ-4+). The data from both questionnaire types were submitted to multivariate normal mixture analysis, which was carried out on factor scores obtained from a three-factor model of SPD criteria; these results supported the hypothesis that SPD is taxonic. The same was true of Study 2, which administered the Semi-structured Interview for DSM-III-R Personality Disorders (SIDP-R) to an independent sample of 537 consecutively admitted outpatients. Similar findings were observed in Study 3, in which the SIDP-R was administered to 225 non-clinical subjects. The results show that the typology of DSM III-R and -IV SPD diagnosis is consistent with the latent structure of SPD features.

Schizotypy: a vulnerability factor for traumatic intrusions

Intrusive mental experiences occur within posttraumatic stress disorder (PTSD) and some psychotic disorders. Similarities in the phenomenology and content in the intrusions of both disorders have been noted. Currently there is little understanding of any common etiology in terms of information-processing styles. This study investigated predictors of analogue posttraumatic intrusive cognitions within a nonclinical sample, including schizotypy, dissociation, and trauma history. Forty-two participants watched a trauma video and recorded trauma-related intrusions occurring for 1 week. More reported intrusive experiences were associated with high positive symptom schizotypy. Our findings are discussed in relation to the possible role of trauma-related intrusions within psychotic disorders.

Finding the "genuine" schizotype: a model and method for resolving heterogeneity in performance on laboratory measures in experimental psychopathology research

Heterogeneity in the performance of persons affected with schizophrenia or schizotypic psychopathology on various laboratory tasks has long been recognized, both for its consistency across tasks and studies and for the massive methodological and substantive challenges it poses for experimental psychopathology, genetic, and other investigations. Traditional multivariate techniques, such as factor analysis, discriminant function analysis, and cluster analysis, have all been deemed inadequate for resolving heterogeneity, because of one or another statistical limitation. Here, an objective statistical approach based on a formal statistical model that uses the ubiquitous and well-developed expectation-maximization (EM) algorithm (A. P. Dempster, N. M. Laird, & D. B. Rubin, 1977) is presented, which enables one effectively to partition a group of experimental subjects, in this case identified initially using the well-known Perceptual Aberration Scale (L. J. Chapman, J. P. Chapman, & M. L. Raulin, 1978), in a manner that reduces heterogeneity and allows for the separation of what are termed genuine and false-positive schizotypes. The validity of the parsing strategy was supported by reference to other laboratory indexes of relevance to schizophrenia and schizotypy that were not included in the initial EM-based analyses. The potential utility of this approach is discussed with reference to future schizophrenia and schizotypy research.

Psychosis proneness and ADHD in young relatives of schizophrenia patients

Symptoms resembling the attentional deficit hyperactivity disorder (ADHD) are frequently observed in young relatives at risk for schizophrenia (HR). We examined the frequency of the ADHD syndrome and its relationship to psychosis related psychopathology and neurobehavioral abnormalities in young HR subjects (n=29) and healthy comparison subjects (HC; n=30). Thirty-one percent of HR subjects (n=9) had ADHD as a lifetime Axis-I diagnosis (HR-A). Compared to healthy comparison subjects, the HR-A group had impaired neurological function. The HR-A group but not the HR subjects without ADHD had higher scores on the Chapman's magical ideation and perceptual aberration scales. Thus, ADHD-like features are more prevalent in the HR population than the one described in the general population and are associated with more frequent psychosis-like clinical features. Longitudinal studies can clarify whether an "ADHD subgroup" within HR subjects predict an increased risk for future emergence of schizophrenia.

Variants of the MMPI 2-7-8 code type: schizotypal correlates of high point 2, 7, or 8

Our study sought to evaluate whether examination of the high-point scale among subjects with a 2-7-8 parent configuration on the MMPI could assist in the identification of individuals with schizotypal features. Additionally, this study compared male 2-7-8 subjects to female 2-7-8 subjects to determine whether gender mediates endorsement of items associated with these features. Subjects (N = 106) who produced a 2-7-8 parent profile were subdivided according to high point (2, 7, or 8), and the three subgroups were subsequently compared on other self-report measures associated with schizotypal attributes. Subgroup comparisons revealed that the High 8 and High 2 groups produced a pattern of responding consistent with schizotypal characteristics. In contrast, the at-risk status of the High 7 group appears doubtful. Comparisons based on gender generally revealed no differences among female and male 2-7-8 subjects.

Longitudinal changes in IQ among fragile X males: clinical evidence of more than one mutation?

Longitudinal changes in IQ among mentally retarded (MR) fragile X [fra(x)] males have been reported previously. While age is associated with decline in IQ, not all males are so affected. This suggests that there may be more than one subtype of affected fra(X) male. Therefore, we examined the distribution of standardized difference scores (Zdiff) in IQ to determine if subjects were from an admixture of at least 2 populations. Cluster analysis of Zdiff scores was used to partition subjects into 2 groups. Goodness-of-fit tests indicated that scores were more likely to come from an admixture. Discriminant functions (DF) were calculated to determine predictive validity of Zdiff scores. To eliminate the effect of skewing, a power transform was applied to Zdiff scores and DFs recomputed. Zdiff and transformed scores provided similar results. The mean and variance for one group showed no differences in test-retest scores as would be expected from examining any population while the mean for the second group indicated significant decline in IQ nearly 4 standard errors below the first test score. These results suggest that there may be clinical evidence for 2 types of fra(X) mutation: One which causes MR but is static, and a second mutation which causes MR but is dynamic and contributes to an apparent longitudinal decline in cognitive function.

Confirming schizotypic personality configurations in hypothetically psychosis-prone university students

The personality features of hypothetically psychosis-prone (or schizotypic) subjects were examined. Schizotypic (n = 32) and control (n = 44) subjects were identified within a pool of 726 randomly ascertained nonclinical university students who had completed the Perceptual Aberration Scale (PAS) during a large-scale screening study. Approximately 4-6 months after the initial screening, the schizotypic and control subjects completed the Minnesota Multiphasic Personality Inventory (MMPI). Schizotypic subjects as a group displayed an average MMPI profile consistent with schizotypic personality features, whereas the control subjects did not. Moreover, multivariate profile analysis revealed that the schizotypic group MMPI profile differed significantly in shape from the control group profile. Finally, schizophrenia-related MMPI high-point codes were five times as prevalent among the PAS-identified schizotypic subjects as among the controls. The results suggest that the PAS identifies individuals who show schizotypic personality MMPI configurations and may carry a latent vulnerability for schizophrenia or, more broadly, psychosis.