Transmission of a psychometric indicator for liability to schizophrenia in normal families

Differentiation of adoptees at high versus low genetic risk for schizophrenia by adjusted MMPI indices

The aim of this study was to find potential signs of genetic vulnerability to schizophrenia. The differences between adoptees at high genetic risk for schizophrenia (their biological mother had a schizophrenia spectrum disorder) and control adoptees of non-schizophrenia spectrum biological mothers were assessed. The comparisons between these groups were based on the Minnesota Multiphasic Personality Inventory (MMPI) test's subscale scores adjusted by gender, age at MMPI assessment, age at placement into the adoptive family and social class. The subjects were a subsamples of a total of 182 tested adoptees and 136 mentally healthy adoptees in the Finnish Adoptive Family Study. The high-risk group was found to be distinguishable from the low-risk group based on deviant scores on the Hostility, Hypomania and Lie scales. These scales may measure genetic vulnerability and also possibly be indicative of psychometric deviance predicting future onset of schizophrenia.

Premorbid self-disorders and lifetime diagnosis in the schizophrenia spectrum: a prospective high-risk study

AIM

The notion of a disordered self as a core disturbance of schizophrenia was proposed in many foundational texts. Recent studies, spurred by the development of the Examination of Anomalous Self-Experience (EASE), seem to indicate that self-disorders are a specific manifestation of schizophrenia vulnerability. Follow-up studies of help-seeking, prodromal and first-admission patients have demonstrated the utility of self-disorders for predicting later schizophrenia-spectrum disturbance. We wished to extend these findings by gauging the predictive value of self-disorders in a premorbid, non-clinical population at high risk for schizophrenia.

METHODS

Children from the Copenhagen High-Risk Project with high-genetic risk for schizophrenia (N = 212) were assessed premorbidly (average age = 15), and diagnostically re-evaluated after 10 and 25 years. Since the EASE was not available at the time of premorbid assessment, we hypothesized that a proxy scale drawn from the Minnesota Multiphasic Personality Inventory (MMPI) could distinguish those who later developed a schizophrenia-spectrum disorder (N = 68) from those who remained healthy (N = 64). The Self-Disorder Scale comprised 32 items whose content suggested an aspect of self-disorder as measured by the EASE.

RESULTS

Premorbid Self-Disorder Scale scores significantly predicted lifetime schizophrenia-spectrum diagnosis in the high-risk cohort. Although there was considerable item overlap between the new scale and an existing MMPI scale (psychoticism), the overlap did not account for the Self-Disorder Scale's predictive efficacy.

CONCLUSION

The results support the notion of self-disorders as a core vulnerability feature in schizophrenia, detectable premorbidly in those developing later schizophrenia-spectrum disorders.

Schizotypy and personality profiles of Cluster A in a group of schizophrenic patients and their siblings

BACKGROUND

Schizotypy, or the set of personality traits related to schizophrenia, is considered an endophenotypic manifestation that is more represented in first-degree relatives of patients with schizophrenia than in the general population. The assessment of schizotypy is primarily based on self-reports, and for this reason it presents several limitations. In order to assess schizotypy, this study proposes a diagnostic instrument based on clinical reports.

METHODS

A sample of 66 subjects, composed of 25 outpatients with schizophrenia, 18 siblings of these patients and 23 healthy controls, was subjected to the personality assessment test SWAP-200 by trained clinical interviewers. To test the hypothesis of the difference between the profiles of the Personality Disorders within the schizophrenia spectrum, a Multivariate Analysis of Variance and subsequent planned comparisons were conducted.

RESULTS

Patients with schizophrenia scored higher than both their siblings and the controls on all SWAP-200 scales; their siblings, compared to the healthy controls, showed significant statistical differences, with higher mean scores for paranoid (F(1,63) = 7.02; p = 0.01), schizoid (F(1,63) = 6.56; p = 0.013) and schizotypal (F(1,63) = 6.47; p = 0.013) traits (PD T scores of Cluster A and Q-factor scores for the schizoid scale [F(1,63) = 6.47; p = 0.013]).

CONCLUSIONS

Consistent with previous data, first-degree relatives of patients with schizophrenia scored higher on schizophrenia-related personality traits than a general population comparison sample. SWAP-200, as an alternative diagnostic instrument to self-report measures, is able to reveal the higher prevalence of schizotypal traits in siblings of patients with schizophrenia, suggesting its possible use as a complementary instrument for the assessment of schizophrenia.

MMPI measures as signs of predisposition to mental disorder among adoptees at high risk for schizophrenia

The DSM-III-R diagnoses of a group of adoptees were predicted by the MMPI (Minnesota Multiphasic Personality Inventory) schizophrenia-related scales in the Finnish Adoptive Family Study. The sample consisted of 60 high-risk (HR) adopted-away offspring of biologic mothers with a diagnosis of broad schizophrenia spectrum and 76 low-risk (LR) control adoptees. They were assessed with the MMPI before the onset of any psychiatric disorder at a mean age of 24 years. High scores on the Psychopathic Deviate scale predicted psychiatric disorder at 11-year follow-up. Furthermore, LR adoptees', but not HR adoptees', mental disorders could be predicted with the MMPI scales Psychopathic Deviate and Golden-Meehl Indicators. These scales measure schizophrenia-related personality traits, including a social behavior, anhedonia, ambivalence, interpersonal aversiveness, and formal thought disturbances.

Interaction of genetic vulnerability to schizophrenia and Communication Deviance of adoptive parents associated with MMPI schizophrenia vulnerability indicators of adoptees

The aim of this study was to establish possible genotype-environment interaction in high-risk and low-risk adoptees' vulnerability to schizophrenia. The study population consisted of a subgroup of 41 adoptive families with a high genetic risk adoptee and 58 families with a low genetic risk adoptee from the Finnish Adoptive Family Study of Schizophrenia. Communication style was assessed based on the Communication Deviance (CD) of the adoptive parents, and the adoptees' vulnerability indicators were measured with the Minnesota Multiphasic Personality Inventory (MMPI). Taken separately, only the genetic liability to schizophrenia, but not the communication style of the adoptive parents, was significantly associated with the Lie, Correction and Hostility scales in the MMPI of the adoptees. Analyses of the genotype-environment interactions showed that the high-risk adoptees with high-CD rearing parents had an increased risk of vulnerability on the MMPI Social Maladjustment scale compared with the corresponding low-risk adoptees. Genetic vulnerability to schizophrenia and genotype-environment interaction are manifested in adoptees' MMPI.

Psychometric Deviance Measured by MMPI in Adoptees at High Risk for Schizophrenia and Their Adoptive Controls

Psychometric deviance in personality traits as assessed by the Minnesota Multiphasic Personality Inventory (MMPI; Dahlstrom, Welsh, & Dahlstrom, 1982) was compared between adopted-away, high-risk (HR) offspring of schizophrenic biologic mothers and low-risk (LR) controls. A subsample of the Finnish Adoptive Family Study (Tienari et al., 2000) included 60 HR adoptees and 76 LR control adoptees who were tested by the MMPI before the onset of any psychiatric disorder at the mean age of 24 years. The HR group was found to be distinguishable based on deviant scores on the scales HOS and HYP, indicating emotional unresponsiveness, restricted affectivity, and decreased energy. These may also be considered possible premorbid and prodromal signs of future schizophrenia among the HR adoptees.

Mixture distributions in human genetics research

The use of mixture distributions in genetics research dates back to at least the late 1800s when Karl Pearson applied them in an analysis of crab morphometry. Pearson's use of normal mixture distributions to model the mixing of different species of crab (or 'families' of crab as he referred to them) within a defined geographic area motivated further use of mixture distributions in genetics research settings, and ultimately led to their development and recognition as intuitive modelling devices for the effects of underlying genes on quantitative phenotypic (i.e. trait) expression. In addition, mixture distributions are now used routinely to model or accommodate the genetic heterogeneity thought to underlie many human diseases. Specific applications of mixture distribution models in contemporary human genetics research are, in fact, too numerous to count. Despite this long, consistent and arguably illustrious history of use, little mention of mixture distributions in genetics research is made in many recent reviews on mixture models. This review attempts to rectify this by providing insight into the role that mixture distributions play in contemporary human genetics research. Tables providing examples from the literature that describe applications of mixture models in human genetics research are offered as a way of acquainting the interested reader with relevant studies. In addition, some of the more problematic aspects of the use of mixture models in genetics research are outlined and addressed.

Commingling and segregation analysis of reading performance in families of normal reading probands

This paper reports the results of commingling and genetic segregation analyses performed on a quantitative reading phenotype in 125 families ascertained through normal, nondisabled readers. Commingling analysis using SKUMIX suggested that the reading phenotype best fit a skewed, single distribution model. Complex segregation using POINTER was then performed on the power adjusted data. While there were some analytical ambiguities and complexities, the segregation analysis indicated that there was familial transmission of the phenotype and that a significant percentage of the variance in this phenotype could be attributed to a major gene with dominance. Because the estimated frequency of the putative dominant allele is .35, 57% of the population would carry at least one copy of this allele. This common allele, with low penetrance, accounted for 54% of the phenotypic variance in reading scores. These findings are considered in the context of our earlier report of major gene influence ona qualitative dyslexic phenotype in a sample of 133 dyslexic proband families that were originally matched to the present sample of control families (Pennington et al., 1991). The applicability of a classic single gene, multifactorial-polygenic, and oligogenic or QTL models for reading ability/disability is discussed.

Familial resemblance of schizotypic traits

The goal of this study was to examine the familial resemblance of schizotypic traits, and to explore whether different schizotypic traits are familially related to one another. Several of the Chapmans' psychosis proneness scales were administered to a group of college students and their families. Evidence of at least some familial resemblance was found for both physical anhedonia and perceptual aberration, though it was stronger for anhedonia. Anhedonia and perceptual aberration appeared to be familially influenced independently of one another. Finally, the results indicated that offspring resembled their mothers more than they resembled their fathers on both anhedonia and perceptual aberration.

The genetics of personality disorder

Most measurable aspects of normal personality appear to be at least moderately heritable, with direct evidence coming from family, twin and adoption studies and indirect support deriving from psychophysiological research and breeding experiments on animals. Interestingly, genetic studies also shed light on the environmental sources of variation in personality and suggest that shared family environment rarely, if ever, has any positive effect on similarity between relatives. Despite problems of classification, and variations in the use of terms, a survey of the literature provides reasonably consistent evidence of a genetic contribution to several categories of abnormal personality, which we here divide into three groups, antisocial, anxious/avoidant, and schizoid-schizotypal personalities. However, personality disorders are complex traits that do not show simple mendelian patterns of inheritance and so far molecular genetics has been of no help in understanding their aetiology. Fortunately, techniques are now becoming available that enable the detection and potential localisation of genes of small effect and which may help elucidate the molecular basis even of (probably) polygenic traits such as abnormal personality.

Current perspectives on the genetics of unipolar depression

Evidence regarding the heritability of unipolar depression is evaluated. The data reviewed here support the involvement of genetic factors in the etiology of unipolar depression and its suitability for independent genetic inquiry, despite our inability to identify the mode(s) of transmission or identify a candidate locus. Continued progress in testing etiologic hypotheses requires (a) clarification of the mode of transmission; (b) resolution of phenotypic and potential genotypic heterogeneity; (c) general agreement on a "gold standard" for assessment of the unipolar phenotype; (d) the continued application of available quantitative methods to take into account the effects of ascertainment bias, sex effects, cohort effects, and variable/late age at onset; and (e) incorporation of quantitative indicators correlated with liability in multivariate analysis to improve the stability/validity of phenotypic determinations in segregation and linkage analysis. We present several recommendations regarding the extension of current methodologies in human population and quantitative genetics to help resolve these issues.

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.

Discerning the latent structure of hypothetical psychosis proneness through admixture analysis

The application of psychometric procedures to a normal population sample to detect individuals with increased liability for schizophrenia is a useful methodological adjunct to the traditional genetic high-risk strategy. A necessary and reasonable step in the process of establishing the utility of a viable psychometric index of schizotypy is the formal investigation of the latent structure of psychometric values. The present study used admixture analysis to examine the distribution of scores on the Perceptual Aberration Scale (PAS), an objective measure of hypothetical psychosis-proneness, in a randomly ascertained sample of 18-year-old university students (n = 707). We applied parametric methods that assumed normally distributed component distributions; viewed in this context, our results are hypothesis-generating and not definitive confirmation of specific hypotheses. Within our methodological framework, the results provide strong evidence for the commingling of normal distributions, even after allowing for unequal variances across components and after removing skewness. The overall distribution of power-transformed data is consistent with the existence of three qualitatively distinct classes of PAS responders. We discuss our results in light of Meehl's model of schizotaxia, a "mixed model" of inheritance of liability to schizophrenia, and we review the methodological implications of our findings for future research.

Psychometric deviance in offspring at risk for schizophrenia: II. Resolving heterogeneity through admixture analysis

The longitudinal and prospective study of offspring at risk for schizophrenia is complicated by within-group heterogeneity in liability, as only a subgroup of those at risk will ultimately become affected. Here, we attempt to resolve such heterogeneity in the New York High-Risk Project by conducting an admixture analysis of values on a psychometric index of liability to schizophrenia derived from the Minnesota Multiphasic Personality Inventory (MMPI). We fit mixtures of components to the overall distribution in 171 children from three criterion groups: offspring at risk (HR) for schizophrenia, psychiatric comparison (PC) offspring at risk for affective illness, and normal comparison (NC) offspring not at increased risk for psychiatric morbidity. The distribution of psychometric scores was bimodal, and separation of two latent classes showed that there is a valid and nonarbitrary distinction between a subgroup of MMPI-deviant (primarily HR) offspring and a larger homogeneous group of MMPI-nondeviant HR, PC, and NC subjects. While continued followup is required to demonstrate a correspondence between these two classes and an underlying taxonomy of liability to schizophrenia, our findings demonstrate the utility of objective psychometric measurement and admixture analysis for resolving within-group heterogeneity in high-risk research. The wider implications of including our MMPI indicators in other genetic investigations of schizophrenia are discussed.

Estimation of disease risk under bivariate models of multifactorial inheritance

Adjunct consideration of both qualitative (affection status) and quantitative (correlated liability indicator) information to define a bivariate phenotype can increase considerably the accuracy and efficiency of disease risk estimation. A general approach for calculating morbid risks to offspring on the basis of parental affection status and an offspring quantitative trait is presented. We also describe two different bivariate models of multifactorial inheritance, as implemented in the computer programs POINTER and YPOINT, and make explicit their assumptions/constraints when estimating the within-person and parent-offspring correlations necessary for calculation of morbid risks. We use psychometric family data on schizophrenia from the New York High-Risk Project to estimate these correlations and illustrate our methods. Our results show that even when a trait is only moderately correlated with liability, incorporation of quantitative trait information can lead to resolution of a range of risk to offspring that is not possible through reliance on parental affection status alone. Bivariate models provide a useful methodology for incorporating quantitative indicators of liability in the investigation of genetically complex diseases.