The Consortium on the Genetics of Schizophrenia: neurocognitive endophenotypes

Replication of linkage on chromosome 7q22 and association of the regional Reelin gene with working memory in schizophrenia families

Schizophrenia is a common and complex mental disorder. Hereditary factors are important for its etiology, but despite linkage signals reported to several chromosomal regions in different populations, final identification of predisposing genes has remained a challenge. Utilizing a large family-based schizophrenia study sample from Finland, we have identified several linked loci: 1q32.2-q42, 2q, 4q31, 5q and 7q22. In this study, an independent sample of 352 nuclear schizophrenia families (n=1626) allowed replication of linkage on 7q21-32. In a sample of 245 nuclear families (n=1074) originating from the same geographical region as the families revealing the linkage, SNP and microsatellite association analyses of the four regional candidate genes, GRM3, RELN, SEMA3A and VGF, revealed no significant association to the clinical diagnosis of schizophrenia. Instead, quantifiable trait component analyses with neuropsychological endophenotypes available from 186 nuclear families (n=861) of the sample showed significant association to RELN variants for traits related to verbal (P=0.000003) and visual working memory (P=0.002), memory (P=0.002) and executive functioning (P=0.002). Trait-associated allele-positive subjects scored lower in the tests measuring working memory (P=0.0004-0.0000000004), memory (P=0.02-0.0001) and executive functioning (P=0.001). Our findings suggest that allelic variants of RELN contribute to the endophenotypes of schizophrenia.

Verbal as well as spatial working memory predicts visuospatial processing in male schizophrenia patients

BACKGROUND

Visuospatial processing (VSP) is impaired in schizophrenia. Recent studies showed significant associations between the Judgment of Line Orientation (JLO) test, a common test of VSP and Verbal (VWM) as well as Spatial (SWM) working memory. VWM and SWM show different associations with various genes so subgroups of patients with similar VSP but different WM impairment profiles may vary in genetic associations. In this study we investigated the relationship among VSP, VWM and SWM.

METHODS

Sixty seven men with schizophrenia and 51 healthy men completed computerized JLO and tests of VWM (digit span), and SWM (Dot test). Tests of attention (CPT) and psychomotor processing speed (Finger Tap) were also included.

RESULTS

Patients' performance was impaired on all tests. Multivariate regression with JLO as the outcome variable and VWM, SWM, attention, psychomotor processing speed and interactions between group and these variables, as predictors showed significant contribution of VWM and SWM. The model explained 34.4% of the variance (R(2)=0.344).

CONCLUSION

VSP, as measured by JLO, receives independent contributions from VWM and SWM. Patient subgroups matched for VSP may differ in the relative contributions and impairments of VWM and SWM. Such heterogeneity may limit the usefulness of VSP in genetic studies. The possibility that WM may be more useful than VSP in this regard deserves further study.

Divergent backward masking performance in schizophrenia and bipolar disorder: association with COMT

Schizophrenia has been reliably associated with impairments in backward masking performance, while bipolar disorder has less consistently been tied to such a deficit. To examine the genetic determinants of visual perception abnormalities in schizophrenia and bipolar disorder, this study evaluated the diagnostic specificity of backward masking performance deficits and whether masking deficits were associated with catechol-O-methyl transferase (COMT) genotype. A location-based backward masking task, which equated participants on the perceptual intensity of stimuli, was completed by 41 schizophrenia outpatients, 28 bipolar outpatients, and 43 nonpsychiatric controls. COMT genotype data were available for 39 schizophrenia outpatients, 28 bipolar outpatients, and 20 nonpsychiatric controls. Schizophrenia patients demonstrated impaired backward masking performance compared to controls and bipolar patients. A group by COMT genotype interaction was detected with schizophrenia Met homozygotes performing more poorly than control and bipolar Met homozygotes, and worse than Val homozygote and heterozygote schizophrenia patients. This study provides novel evidence for differential effects of the COMT gene on neural systems underlying visual perception in schizophrenia and bipolar disorder. The COMT Met allele may be associated with deficits in schizophrenia that are unrelated to neural systems supporting sustained attention or working memory.

The validity of Psychosis Proneness Scales as vulnerability indicators in recent-onset schizophrenia patients

The Psychosis Proneness Scales developed by the Chapmans and colleagues [Chapman, J.P., Chapman, L.J., Kwapil, T.R. Scales for the measurement of schizotypy. In: Raine., A., Lencz, T., Mednick, S.A., (Eds.). Schizotypal Personality. New York: Cambridge University Press, 1995. pp. 79-109] are widely used to identify non-patient individuals who are hypothesized to possess heightened vulnerability to schizophrenia and related psychopathology. Yet surprisingly little is known about whether schizophrenia patients themselves show abnormalities on these scales across different clinical states, as would be expected for vulnerability indicators. Scores on four of the Psychosis Proneness Scales were evaluated at three assessment points over a 15-month period in healthy controls (n=54) and in recent-onset schizophrenia patients (n=72) who experienced symptom fluctuations across assessments. Patients showed steady elevations on the Physical Anhedonia Scale across time and clinical state, consistent with a stable vulnerability indicator. Patients had higher scores on the Perceptual Aberration and Magical Ideation Scales than controls throughout the follow-up period but scores also changed across clinical states, consistent with a mediating vulnerability indicator. Patients had higher scores on the Impulsive Non-Conformity Scale than controls only during a psychotic state, reflecting an episode indicator. The longitudinal characteristics of these scales in people who are actually diagnosed with schizophrenia provide key evidence for the validity of three commonly used psychometric indicators of vulnerability to psychosis.

Schizophrenia, "Just the Facts": what we know in 2008 part 1: overview

For every disorder, there is a set of established findings and accepted constructs upon which further understanding is built. The concept of schizophrenia as a disease entity has been with us for a little more than a century, although descriptions resembling this condition predate this conceptualization. In 1988, for the inaugural issue of Schizophrenia Research, at the invitation of the founding editors, a senior researcher, since deceased (RJ Wyatt) published a summary of generally accepted ideas about the disorder, which he termed "the facts" of schizophrenia. Ten years later, in conjunction with two of the authors (MSK, RT), he compiled a more extensive set of "facts" for the purpose of evaluating conceptual models or theoretical constructs developed to understand the nature of schizophrenia. On the 20th anniversary of this journal, we update and substantially expand our effort to periodically summarize the current body of information about schizophrenia. We compile a body of seventy-seven representative major findings and group them in terms of their specific relevance to schizophrenia -- etiologies, pathophysiology, clinical manifestations, and treatments. We rate each such "fact" on a 0-3 scale for measures of reproducibility, whether primary to schizophrenia, and durability over time. We also pose one or more critical questions with reference to each "fact", answers to which might help better elucidate the meaning of that finding for our understanding of schizophrenia. We intend to follow this paper with the submission to the journal of a series of topic-specific articles, critically reviewing the evidence.

Effects of acute metabolic stress on the dopaminergic and pituitary-adrenal axis activity in patients with schizophrenia, their unaffected siblings and controls

A genetically mediated abnormal sensitivity to stress is thought to play a role in the onset, exacerbation and relapse of schizophrenia. In a double blind, placebo-controlled crossover study, peak increases in plasma ACTH (Delta ACTH) and homovanillic-acid, a dopamine metabolite, (Delta HVA) following exposure to a metabolic stressor(2DG) were studied in unaffected siblings of patients with schizophrenia (n=15), their patient relatives (n=15) and healthy controls (n=14). Siblings showed a stress response (both Delta ACTH and Delta HVA) that was significantly greater compared to controls and significantly less pronounced compared to patients. The results suggest that the genetic risk for schizophrenia may be characterized by an enhanced sensitivity to stress.

Dimensions of impulsivity are associated with poor spatial working memory performance in monkeys

Impulsive behavior and novelty seeking are dimensions of temperament that are behavioral determinants of risk for attention deficit/hyperactivity disorder and its neurocognitive endophenotypes, and variation in the dopamine D4 receptor gene (DRD4) explains at least a portion of the variance in the traits. To further characterize the dimensional phenotype associated with impulsiveness, adolescent male monkeys were evaluated using ecologically valid tests of impulsive approach and aggression in response to social or nonsocial stimuli; subsequently, a delayed response task was implemented to assess spatial working memory performance. Subjects were selected into this study based on their response to the social challenge task or by DRD4 genotype, resulting in three groups: low-impulsivity/common DRD4 allele, high-impulsivity/common DRD4 allele, or rare DRD4 allele. All animals acquired the delayed response task and could perform at near ceiling levels when a approximately 0 s delay version was imposed, but as delays were lengthened, high-impulsive animals, regardless of DRD4 genotype, made fewer correct responses than did low-impulsive subjects; an inverse relationship existed for working memory and impulsivity. Notably, impulsive behavior evoked by social and nonsocial stimuli explained overlapping and independent portions of the variance in working memory performance. CSF levels of monoamine metabolites did not significantly differentiate the high- and low-impulsive animals, although monkeys carrying the DRD4 rare allele tended to exhibit higher monoamine turnover. These data indicate that dimensions of impulsivity may impact on working memory performance in qualitatively similar ways but through different mechanisms.

Deficits in facial affect recognition in unaffected siblings of Xhosa schizophrenia patients: evidence for a neurocognitive endophenotype

The present study in an African Xhosa sample examined whether familial vulnerability to schizophrenia is associated with deficits in facial affect recognition. Healthy comparison subjects, unaffected siblings of schizophrenia patients, and schizophrenia patients were tested with a task requiring rapid recognition of matched positive (happy), negative (angry), and neutral facial expressions. Siblings and patients demonstrated impaired recognition of negative relative to positive facial expressions whereas comparison subjects recognized negative and positive expressions at an equal level of accuracy. These results suggest that deficits in the processing negative affect from social cues are transmitted in families and may represent a heritable endophenotype of schizophrenia.

The stability of inhibitory and working memory deficits in children and adolescents who are children of parents with schizophrenia

Cognitive deficits are a central feature of schizophrenia and occur in first-degree relatives of schizophrenic probands, even in the absence of psychotic symptoms. A number of cognitive domains have been implicated including measures of response inhibition and working memory. While the stability of cognitive deficits has been demonstrated in individuals with schizophrenia, stability of deficits has not been explored in first-degree relatives. This report focuses on 25 children (ages 6-15 years), all with at least one schizophrenic parent. The children were assessed twice, utilizing inhibitory and working memory tasks, with a mean 2.6 years between visits. Stop reaction time (a measure of motor inhibition) and performance on a counting span task (a measure of verbal working memory) were borderline to mildly impaired (compared with a typically developing comparison group) at both visits with similar effect sizes (stopping task time 1, effect size = 0.46, time 2 effect size = 0.50; counting span time 1 effect size = 0.53, time 2 effect size = 0.42). For these 2 tasks, individual age-adjusted scores also correlated across both time points (r = 0.41-0.76) suggesting that individual children maintained deficits across time. As etiologically driven strategies are developed for the cognitive deficits of schizophrenia, expansion of these treatments to relatives who share the cognitive but not the psychotic symptoms may be worth exploring.

Initial heritability analyses of endophenotypic measures for schizophrenia: the consortium on the genetics of schizophrenia

CONTEXT

Exploration of the genetic architecture of specific endophenotypes may be a powerful strategy for understanding the genetic basis of schizophrenia.

OBJECTIVE

To characterize the genetic architecture of some key endophenotypic measures selected for their reported heritabilities in schizophrenia.

DESIGN

Family-based heritability study.

SETTING

Seven sites across the United States.

PARTICIPANTS

At the time of these initial data analyses, the members of 183 nuclear families ascertained through probands with schizophrenia had been assessed for these endophenotypes.

MAIN OUTCOME MEASURES

Variance component models were used to assess the heritability of and the environmental and genetic correlations among the endophenotypes. The Consortium on the Genetics of Schizophrenia assesses the neurophysiologic measures of prepulse inhibition of acoustic startle, P50 event-related potential suppression, and the antisaccade task for eye movements and the neurocognitive measures of the Continuous Performance Test (Degraded Stimulus version), the California Verbal Learning Test, the Letter-Number Sequencing test, and 6 measures from the University of Pennsylvania Computerized Neurocognitive Battery. The heritabilities of these 12 measures are the focus of this article.

RESULTS

All of the endophenotypes and the University of Pennsylvania Computerized Neurocognitive Battery measures were found to be significantly heritable (P < or = .005), with heritabilities ranging from 24% to 55%. Significant environmental and genetic correlations were also observed between many of the endophenotypic measures.

CONCLUSION

This is the first large-scale, multisite, family-based heritability study of a collection of endophenotypes for schizophrenia and suggests that endophenotypes are important measures to consider in characterizing the genetic basis of schizophrenia.

Working memory in siblings of schizophrenia patients

Working memory (WM) has hardly been explored in non-psychotic relatives of schizophrenic patients despite its potential suitability as a neurocognitive endophenotype. Indeed, WM modalities, components and processes have rarely been compared in the same group of relatives. The present study examined neurocognitive performance in healthy siblings of schizophrenic patients, including both spatial and verbal WM modalities and tests tapping maintenance (Spatial Span Backwards and CPT-IP d') and manipulative (Letters and Numbers Sequencing) WM processes.

METHODS

68 schizophrenia patients, 38 healthy siblings and 63 controls were assessed on IQ, attention, memory, WM, and executive functions. Cluster A symptoms were screened out in siblings and controls.

RESULTS

Siblings had an intermediate performance between that of schizophrenic patients and controls. They performed worse than controls on IQ, LNS, animal naming, backwards spatial span, phonemic fluency, numbers d', and forward spatial span.

DISCUSSION

Consistent with the WM literature in schizophrenia, both verbal and spatial WM differed significantly between siblings and controls, suggesting that WM deficits are modality independent. Our results failed to support the hypothesis that tests tapping WM manipulative processes heavily loading on DLFPC are quantitatively more impaired in relatives and, therefore, more sensitive to liability for schizophrenia. However, firm conclusions cannot be drawn until more studies assessing both maintenance and manipulative WM processes in relatives are available.

Impairment in error monitoring predicts poor executive function in schizophrenia patients

BACKGROUND

Impaired ability to detect and correct errors may contribute to poor cognitive and social function in schizophrenia.

OBJECTIVE

To test the hypothesis that impairment in error monitoring contributes to impaired executive function in schizophrenia.

METHODS

56 schizophrenia patients and 77 healthy individuals were tested with the Penn Conditional Exclusion test (PCET), a computerised test of executive function which allowed collection of accuracy and latency performance parameters. Error monitoring was assessed by analyzing reaction times for correct (RTC) and incorrect (RTI) responses. Tests of face recognition, working memory (WM) and processing speed were also administered.

RESULTS

Executive error-monitoring effort (EXER), calculated by dividing the difference between RTI and RTC by the sum of RTC and RTI, was significantly smaller in patients than controls. A regression model with the executive function (PCET total errors) as dependent variable showed independent contributions of EXER, verbal WM and spatial WM to test performance and explained 35% of the variance. EXER showed significant association with error-monitoring effort for face recognition in patients but not controls.

CONCLUSION

Impaired error-monitoring contributes to poor executive function in schizophrenia. Independent contributions of error-monitoring effort and verbal WM to executive functions may reflect distinct contributions of prefrontal and medial frontal cortical dysfunctions. Error-monitoring mechanisms in different cognitive domains may share more neural resources in schizophrenia than in healthy individuals, reflecting inefficient processing.

Statistical genetics concepts and approaches in schizophrenia and related neuropsychiatric research

Statistical genetics is a research field that focuses on mathematical models and statistical inference methodologies that relate genetic variations (ie, naturally occurring human DNA sequence variations or "polymorphisms") to particular traits or diseases (phenotypes) usually from data collected on large samples of families or individuals. The ultimate goal of such analysis is the identification of genes and genetic variations that influence disease susceptibility. Although of extreme interest and importance, the fact that many genes and environmental factors contribute to neuropsychiatric diseases of public health importance (eg, schizophrenia, bipolar disorder, and depression) complicates relevant studies and suggests that very sophisticated mathematical and statistical modeling may be required. In addition, large-scale contemporary human DNA sequencing and related projects, such as the Human Genome Project and the International HapMap Project, as well as the development of high-throughput DNA sequencing and genotyping technologies have provided statistical geneticists with a great deal of very relevant and appropriate information and resources. Unfortunately, the use of these resources and their interpretation are not straightforward when applied to complex, multifactorial diseases such as schizophrenia. In this brief and largely nonmathematical review of the field of statistical genetics, we describe many of the main concepts, definitions, and issues that motivate contemporary research. We also provide a discussion of the most pressing contemporary problems that demand further research if progress is to be made in the identification of genes and genetic variations that predispose to complex neuropsychiatric diseases.

Deconstructing schizophrenia: an overview of the use of endophenotypes in order to understand a complex disorder

The genetics of schizophrenia has been approached utilizing a variety of methods. One emerging strategy is the use of endophenotypes in order to understand and identify the functional importance of genetically transmitted, brain-based deficits across schizophrenia kindreds. The endophenotype strategy is a topic of this issue of Schizophrenia Bulletin. Endophenotypes are quantitative, heritable, trait-related deficits typically assessed by laboratory-based methods rather than clinical observation. Endophenotypes are seen as closer to genetic variation than are clinical symptoms of schizophrenia, and are therefore closely linked to heritable risk factors. There has been a broad expansion of opportunities available to psychiatric neuroscientists who use the endophenotype strategy to understand the genetic basis of schizophrenia. In this context, genetic variation such as single nucleotide polymorphisms (SNPs) induces abnormalities in endophenotypic domains such as neurocognition, neurodevelopment, metabolism, and neurophysiology. This article discusses the challenges that abound in genetic research of schizophrenia, including issues in ascertainment, epistasis, ethnic diversity, and the potentially normalizing effects of second-generation antipsychotic medications on neurocognitive and neurophysiological measures. Robust strategies for meeting these challenges are discussed in this review and the subsequent articles in this issue. This article summarizes conceptual advances and progress in the measurement and use of endophenotypes in schizophrenia that form the basis of the multisite National Institute of Mental Health Consortium on the Genetics of Schizophrenia. The endophenotype strategy offers powerful and exciting opportunities to understand the genetically conferred neurobiological vulnerabilities and possible new strong inference and molecularly based treatments for schizophrenia.