Consortium On The Genetics Of Schizophrenia Research Articles

The effects of age and sex on cognitive impairment in schizophrenia: Findings from the Consortium on the Genetics of Schizophrenia (COGS) study.

Recently emerging evidence indicates accelerated age-related changes in the structure and function of the brain in schizophrenia, raising a question about its potential consequences on cognitive function. Using a large sample of schizophrenia patients and controls and a battery of tasks across multiple cognitive domains, we examined whether patients show accelerated age-related decline in cognition and whether an age-related effect differ between females and males. We utilized data of 1,415 schizophrenia patients and 1,062 healthy community collected by the second phase of the Consortium on the Genetics of Schizophrenia (COGS-2). A battery of cognitive tasks included the Letter-Number Span Task, two forms of the Continuous Performance Test, the California Verbal Learning Test, Second Edition, the Penn Emotion Identification Test and the Penn Facial Memory Test. The effect of age and gender on cognitive performance was examined with a general linear model. We observed age-related changes on most cognitive measures, which was similar between males and females. Compared to controls, patients showed greater deterioration in performance on attention/vigilance and greater slowness of processing social information with increasing age. However, controls showed greater age-related changes in working memory and verbal memory compared to patients. Age-related changes (η2p of 0.001 to .008) were much smaller than between-group differences (η2p of 0.005 to .037). This study found that patients showed continued decline of cognition on some domains but stable impairment or even less decline on other domains with increasing age. These findings indicate that age-related changes in cognition in schizophrenia are subtle and not uniform across multiple cognitive domains.

Genome-wide Association of Endophenotypes for Schizophrenia From the Consortium on the Genetics of Schizophrenia (COGS) Study

The Consortium on the Genetics of Schizophrenia (COGS) uses quantitative neurophysiological and neurocognitive endophenotypes with demonstrated deficits in schizophrenia as a platform from which to explore the underlying neural circuitry and genetic architecture. Many of these endophenotypes are associated with poor functional outcome in schizophrenia. Some are also endorsed as potential treatment targets by the US Food and Drug Administration. To build on prior assessments of heritability, association, and linkage in the COGS phase 1 (COGS-1) families by reporting a genome-wide association study (GWAS) of 11 schizophrenia-related endophenotypes in the independent phase 2 (COGS-2) cohort of patients with schizophrenia and healthy comparison participants (HCPs). A total of 1789 patients with schizophrenia and HCPs of self-reported European or Latino ancestry were recruited through a collaborative effort across the COGS sites and genotyped using the PsychChip. Standard quality control filters were applied, and more than 6.2 million variants with a genotyping call rate of greater than 0.99 were available after imputation. Association was performed for data sets stratified by diagnosis and ancestry using linear regression and adjusting for age, sex, and 5 principal components, with results combined through weighted meta-analysis. Data for COGS-1 were collected from January 6, 2003, to August 6, 2008; data for COGS-2, from June 30, 2010, to February 14, 2014. Data were analyzed from October 28, 2016, to May 4, 2018. A genome-wide association study was performed to evaluate association for 11 neurophysiological and neurocognitive endophenotypes targeting key domains of schizophrenia related to inhibition, attention, vigilance, learning, working memory, executive function, episodic memory, and social cognition. The final sample of 1533 participants included 861 male participants (56.2%), and the mean (SD) age was 41.8 (13.6) years. In total, 7 genome-wide significant regions (P < 5 × 10-8) and 2 nearly significant regions (P < 9 × 10-8) containing several genes of interest, including NRG3 and HCN1, were identified for 7 endophenotypes. For each of the 11 endophenotypes, enrichment analyses performed at the level of P < 10-4 compared favorably with previous association results in the COGS-1 families and showed extensive overlap with regions identified for schizophrenia diagnosis. These analyses identified several genomic regions of interest that require further exploration and validation. These data seem to demonstrate the utility of endophenotypes for resolving the genetic architecture of schizophrenia and characterizing the underlying biological dysfunctions. Understanding the molecular basis of these endophenotypes may help to identify novel treatment targets and pave the way for precision-based medicine in schizophrenia and related psychotic disorders.

F186. Characterization of Pre-Deviant Standard Effects on MMN and P3a in Schizophrenia: Findings From Consortium on the Genetics of Schizophrenia (COGS)

F186. Characterization of Pre-Deviant Standard Effects on MMN and P3a in Schizophrenia: Findings From Consortium on the Genetics of Schizophrenia (COGS)

21.2 FAMILIAL RISK FOR SCHIZOPHRENIA

BackgroundLarry Seidman, Ph.D. was a key contributor to the Consortium on the Genetics of Schizophrenia (COGS) with its focus on understanding the genetic substrates of quantitative endophenotypes in schizophrenia patients. With his deep knowledge of neurocognition related to psychosis, Larry was able to help steer the COGS-1 family study of over 300 families. The subsequent COGS-2 case-control study used the same well curated, quality controlled extensive battery of testing with 1411 schizophrenia patients and 1500 extensively tested healthy control subjects. Larry was first author on the 2015 paper “Factor structure and heritability of endophenotypes and schizophrenia: findings from the Consortium on the Genetics of Schizophrenia.” It is important to note that related association studies examined the relationship of quantitative endophenotypes and genetic loci, and this is complementary to but distinct from case-control studies. These COGS studies identified a 42-gene network with a NRGL-ERBB4 hub underlying schizophrenia neurocognitive deficits. Thus, these Ns, modest for case-control studies, are quite powerful for gene finding using quantitative endophenotypic markers related to core “thought disorder” neurocognitive deficits in schizophrenia. These quantitative measures are up to 100 X more efficient and 10 X more powerful for gene finding than case-control studies as explained by Blangero, Williams and Almasy as early as 2005. Genes for SZ overlap with genes for key functionally important quantitative endophenotypes as shown by many groups, including COGENT and COGS, so case-control and endophenotype studies are best viewed as complementary in nature.MethodsSeidman et al (2015) examined 12 heritable neurocognitive and neurophysiological domains (including the Penn CNB Battery), as well as three neurophysiological measures reflecting inhibitory reprocessing from EEG and eye movements. Seidman et al’s analysis revealed five distinct factors in the composite COGS battery. These were 1-episodic memory, 2-working memory, 3-perceptual vigilance, 4-visual abstraction and 5-inhibitory processing. The five factors had similar structures across probands, siblings and controls. Also, heritability was significant for all 5 factors. These composite endophenotype factors will be used to enhance our neurobiological and genetic understanding of schizophrenia and its treatment as we move forward, and are related to the Biotype concept of psychosis. Larry Seidman was also an important contributor to the COGS mission as described below.ResultsThe COGS PsychChip GWAS of quantitative endophenotypes has now identified six regions of association with quantitative neurocognitive measures exceeding genome-wide significance (e.g. NRGL3-Abstaction and Mental Flexibility on the CNB). In addition, many associations between endophenotypes and specific loci exceed the suggestive threshold for further investigation.DiscussionThese data will be presented implicating synaptic plasticity and other crucial CNS processes in endophenotype dysfunction in SZ. NB: COGS interrogates the genetic architecture of endophenotypes associated with SZ and its functional outcome, not schizophrenia per se. Still, there is much overlap between risk genes for SZ and neurocognitive endophenotypes. Also neurocognitive endophenotypes are endorsed by the FDA and MATRICS as treatment targets for schizophrenia itself. This allows for data-guided drug and sensory-cognitive remediation of neurocognitive deficits to improve functional outcome in schizophrenia. Using this genomic information to enhance precision based selection of treatment options now seems to be an exciting and viable new treatment pathway.

21. IDENTIFYING INDIVIDUALS AT HIGH RISK FOR SCHIZOPHRENIA: LJ SEIDMAN MEMORIAL SYMPOSIUM

Overall : Lawrence J. Seidman was born and grew up in New York City. He obtained a PhD from Boston University in Psychology and stayed in Massachusetts to work for many years in the Harvard affiliated Hospitals, such as the VA-Boston Healthcare System, Massachusetts General Hospital and at his untimely passing, he was Professor of Psychology in the Department of Psychiatry at Beth Israel-Deaconess Hospital and the Massachusetts Mental Health Center. He was about to move to a new phase in his career, assuming a position at Children’s Hospital, Boston. He was a pioneer in the fields of the neuropsychology of schizophrenia, ADHD and related disorders, of using the tools of cognitive assessments and brain imaging to understand the genetic predisposition for serious mental illness, and in the last several years—prediction of conversion to psychosis in individuals at high risk. He contributed to many multicenter collaborations and had several collaborators world-wide, playing an important role in their work. This symposium is conducted in his honor with contributions from key collaborators on different aspects of his work. Drs. Tyronne Cannon and Elaine Walker will both represent the North American Prodrome Longitudinal Study (NAPLS) consortium by reviewing its findings in brain imaging and cognition. Dr. David Braff will review the work of the Consortium on the Genetics of Schizophrenia (COGS) multicenter collaboration, in which Dr. Seidman led one of its sites, and Dr. TianHong Zhang from Shanghai will present current data from the Shanghai-Boston SHARP collaboration on early detection of psychosis. The symposium will be concluded by Dr. Keshavan from Beth Israel-Deaconess, who was a close colleague of Dr. Seidman for the last decade. Together they worked side by side exploring many aspects of early detection of schizophrenia and educating trainees and the public on their findings. He will sum up the legacy of Dr. Seidman to the field and how we can continue it into the future.

Deficient prepulse inhibition in schizophrenia in a multi-site cohort: Internal replication and extension

BackgroundThe Consortium on the Genetics of Schizophrenia (COGS) collected case-control endophenotype and genetic information from 2457 patients and healthy subjects (HS) across 5 test sites over 3.5 years. Analysis of the first “wave” (W1) of 1400 subjects identified prepulse inhibition (PPI) deficits in patients vs. HS. Data from the second COGS “wave” (W2), and the combined W(1+2), were used to assess: 1) the replicability of PPI deficits in this design; 2) the impact of response criteria on PPI deficits; and 3) PPI in a large cohort of antipsychotic-free patients. MethodsPPI in W2 HS (n=315) and schizophrenia patients (n=326) was compared to findings from W1; planned analyses assessed the impact of diagnosis, “wave” (1 vs. 2), and startle magnitude criteria. Combining waves allowed us to assess PPI in 120 antipsychotic-free patients, including many in the early course of illness. ResultsANOVA of all W(1+2) subjects revealed robust PPI deficits in patients across “waves” (p<0.0004). Strict response criteria excluded almost 39% of all subjects, disproportionately impacting specific subgroups; ANOVA in this smaller cohort confirmed no significant effect of “wave” or “wave x diagnosis” interaction, and a significant effect of diagnosis (p<0.002). Antipsychotic-free, early-illness patients had particularly robust PPI deficits. DiscussionSchizophrenia-linked PPI deficits were replicable across two multi-site “waves” of subjects collected over 3.5years. Strict response criteria disproportionately excluded older, male, non-Caucasian patients with low-normal hearing acuity. These findings set the stage for genetic analyses of PPI using the combined COGS wave 1 and 2 cohorts.

5.4 From Phenomics to Genomics: The Endophenotype Bridge

Background: Most data sets currently included in genomic analyses of schizophrenia are comprised of case–control design that focuses on diagnostic categorization on those who meet diagnostic criteria for schizophrenia and of healthy participants. A hallmark of schizophrenia is impaired cognitive functioning. The goal of the study was to examine cognitive endophenotypes in 3 large-scale consortia that differ in recruitment and assess the pattern of neurocognitive performance across consortia. Methods: The 3 consortia were family based with different sampling strategies. The Multiplex Investigation of Multigenerational families (MGI) included Caucasian families with at least 2 first-degree relatives with schizophrenia spectrum disorders. The Project Among African-Americans to Explore Risks for Schizophrenia (PAARTNERS) included African American families—affected sibling pairs, TRIOs, or multiplex. The Consortium on the Genetics of Schizophrenia (COGS) included families with a proband, unaffected sibling and both parents (COGS-1) as well as a case–control design (COGS-2). The Penn computerized neurocognitive battery (CNB), based on tasks administered in functional neuroimaging, was administered across consortia. The CNB measures performance accuracy and response time in several domains including: Executive Functions, Episodic Memory, Complex Cognition, Social Cognition and Sensori-Speed. Results: Across consortia, probands with schizophrenia showed a similar pattern of neurocognitive deficits in performance accuracy and speed implicating frontotemporal impairment. Notably, family members manifested mild impairment, intermediate between probands and controls. The neurocognitive parameters were heritable and met established criteria for endophenotypes. Conclusion: Quantitative neurocognitive measures are endophenotypes that can be administered in large-scale consortia and integrated in genomic analyses. Such efforts can advance the understanding of the neurobiology of schizophrenia and be evaluated in treatment studies.

Endophenotypes, Epigenetics, Polygenicity and More: Irv Gottesman's Dynamic Legacy.

First, we describe the hallmark contributions of Irv Gottesman's pioneering scholarship for schizophrenia research including concepts of polygenicity, gene × environment interactions, epigenetics and the endophenotype concept. Gottesman and colleagues' twin studies showed that genes, not social factors, mediate schizophrenia risk. He then showed that schizophrenia is highly polygenic. Next, he introduced the concept of epigenetics into schizophrenia research. Gottesman then introduced the quantitative endophenotype concept. Endophenotypes are laboratory-based measures that show deficits in schizophrenia patients and lesser deficits in their first degree "unaffected" relatives and are viewed as being more proximal to genes and having a simpler genetic architecture than are "fuzzy" qualitative diagnostic disorders. Endophenotypes offer an exciting path to gene discovery, neural circuits, genetic architecture and new treatment pathways of schizophrenia and related psychotic disorders. Second, we were asked to discuss 2 of many endophenotype Consortia and related studies, in order to illustrate the impact of Gottesman's work. We describe the Consortium on the Genetics of Schizophrenia (COGS) exploring neurocognitive and neurophysiological endophenotypes in family and case-control studies. Association, linkage, sequencing and epigenetic studies are described. The Bipolar and Schizophrenia Network for Intermediate Phenotypes (BSNIP) uses an array of endophenotypes including brain imaging in studies across the psychosis dimension, allowing for dimensional analyses. BSNIP results have led to the concept of biotypes, advancing the field. Irv Gottesman was imaginatively prescient in generating novel insights and predicting many major issues which challenge schizophrenia researchers who still use his concepts to guide current research approaches.

Attention/vigilance in schizophrenia: Performance results from a large multi-site study of the Consortium on the Genetics of Schizophrenia (COGS)

Attention/vigilance impairments are present in individuals with schizophrenia across psychotic and remitted states and in their first-degree relatives. An important question is whether deficits in attention/vigilance can be consistently and reliably measured across sites varying in many participant demographic, clinical, and functional characteristics, as needed for large-scale genetic studies of endophenotypes.We examined Continuous Performance Test (CPT) data from phase 2 of the Consortium on the Genetics of Schizophrenia (COGS-2), the largest-scale assessment of cognitive and psychophysiological endophenotypes relevant to schizophrenia. The CPT data from 2251 participants from five sites were examined. A perceptual-load vigilance task (the Degraded Stimulus CPT or DS-CPT) and a memory-load vigilance task (CPT-Identical Pairs or CPT-IP) were utilized.Schizophrenia patients performed more poorly than healthy comparison subjects (HCS) across sites, despite significant site differences in participant age, sex, education, and racial distribution. Patient–HCS differences in signal/noise discrimination (d′) in the DS-CPT varied significantly across sites, but averaged a medium effect size. CPT-IP performance showed large patient–HCS differences across sites. Poor CPT performance was independent of or weakly correlated with symptom severity, but was significantly associated with lower educational achievement and functional capacity. Current smoking was associated with poorer CPT-IP d′. Patients taking both atypical and typical antipsychotic medication performed more poorly than those on no or atypical antipsychotic medications, likely reflecting their greater severity of illness.We conclude that CPT deficits in schizophrenia can be reliably detected across sites, are relatively independent of current symptom severity, and are related to functional capacity.

Robust differences in antisaccade performance exist between COGS schizophrenia cases and controls regardless of recruitment strategies

The impaired ability to make correct antisaccades (i.e., antisaccade performance) is well documented among schizophrenia subjects, and researchers have successfully demonstrated that antisaccade performance is a valid schizophrenia endophenotype that is useful for genetic studies. However, it is unclear how the ascertainment biases that unavoidably result from recruitment differences in schizophrenia subjects identified in family versus case–control studies may influence patient–control differences in antisaccade performance. To assess the impact of ascertainment bias, researchers from the Consortium on the Genetics of Schizophrenia (COGS) compared antisaccade performance and antisaccade metrics (latency and gain) in schizophrenia and control subjects from COGS-1, a family-based schizophrenia study, to schizophrenia and control subjects from COGS-2, a corresponding case–control study. COGS-2 schizophrenia subjects were substantially older; had lower education status, worse psychosocial function, and more severe symptoms; and were three times more likely to be a member of a multiplex family than COGS-1 schizophrenia subjects. Despite these variations, which were likely the result of ascertainment differences (as described in the introduction to this special issue), the effect sizes of the control–schizophrenia differences in antisaccade performance were similar in both studies (Cohen's d effect size of 1.06 and 1.01 in COGS-1 and COGS-2, respectively). This suggests that, in addition to the robust, state-independent schizophrenia-related deficits described in endophenotype studies, group differences in antisaccade performance do not vary based on subject ascertainment and recruitment factors.

California Verbal Learning Test-II performance in schizophrenia as a function of ascertainment strategy: Comparing the first and second phases of the Consortium on the Genetics of Schizophrenia (COGS)

The first phase of the Consortium on the Genetics of Schizophrenia (COGS-1) showed performance deficits in learning and memory on the California Verbal Learning Test, Second Edition (CVLT-II) in individuals with schizophrenia (SZ), compared to healthy comparison subjects (HCS). A question is whether the COGS-1 study, which used a family study design (i.e. studying relatively intact families), yielded “milder” SZ phenotypes than those acquired subsequently in the COGS-2 case–control design that did not recruit unaffected family members. CVLT-II performance was compared for the COGS-1 and COGS-2 samples. Analyses focused on learning, recall and recognition variables, with age, gender and education as covariates. Analyses of COGS-2 data explored effects of additional covariates and moderating factors in CVLT-II performance. 324 SZ subjects and 510 HCS had complete CVLT-II and covariate data in COGS-1, while 1356 SZ and 1036 HCS had complete data in COGS-2. Except for recognition memory, analysis of covariance showed significantly worse performance in COGS-2 on all CVLT-II variables for SZ and HCS, and remained significant in the presence of the covariates. Performance in each of the 5 learning trials differed significantly. However, effect sizes comparing cases and controls were comparable across the two studies. COGS-2 analyses confirmed SZ performance deficits despite effects of multiple significant covariates and moderating factors. CVLT-II performance was worse in COGS-2 than in COGS-1 for both the SZ and the HCS in this large cohort, likely due to cohort effects. Demographically corrected data yield a consistent pattern of performance across the two studies in SZ.

Neurocognitive performance in family-based and case-control studies of schizophrenia

BackgroundNeurocognitive deficits in schizophrenia (SZ) are established and the Consortium on the Genetics of Schizophrenia (COGS) investigated such measures as endophenotypes in family-based (COGS-1) and case-control (COGS-2) studies. By requiring family participation, family-based sampling may result in samples that vary demographically and perform better on neurocognitive measures. MethodsThe Penn computerized neurocognitive battery (CNB) evaluates accuracy and speed of performance for several domains and was administered across sites in COGS-1 and COGS-2. Most tests were included in both studies. COGS-1 included 328 patients with SZ and 497 healthy comparison subjects (HCS) and COGS-2 included 1195 patients and 1009 HCS. ResultsDemographically, COGS-1 participants were younger, more educated, with more educated parents and higher estimated IQ compared to COGS-2 participants. After controlling for demographics, the two samples produced very similar performance profiles compared to their respective controls. As expected, performance was better and with smaller effect sizes compared to controls in COGS-1 relative to COGS-2. Better performance was most pronounced for spatial processing while emotion identification had large effect sizes for both accuracy and speed in both samples. Performance was positively correlated with functioning and negatively with negative and positive symptoms in both samples, but correlations were attenuated in COGS-2, especially with positive symptoms. ConclusionsPatients ascertained through family-based design have more favorable demographics and better performance on some neurocognitive domains. Thus, studies that use case-control ascertainment may tap into populations with more severe forms of illness that are exposed to less favorable factors compared to those ascertained with family-based designs.

Validation of mismatch negativity and P3a for use in multi-site studies of schizophrenia: Characterization of demographic, clinical, cognitive, and functional correlates in COGS-2

Mismatch negativity (MMN) and P3a are auditory event-related potential (ERP) components that show robust deficits in schizophrenia (SZ) patients and exhibit qualities of endophenotypes, including substantial heritability, test–retest reliability, and trait-like stability. These measures also fulfill criteria for use as cognition and function-linked biomarkers in outcome studies, but have not yet been validated for use in large-scale multi-site clinical studies. This study tested the feasibility of adding MMN and P3a to the ongoing Consortium on the Genetics of Schizophrenia (COGS) study. The extent to which demographic, clinical, cognitive, and functional characteristics contribute to variability in MMN and P3a amplitudes was also examined. Participants (HCS n=824, SZ n=966) underwent testing at 5 geographically distributed COGS laboratories. Valid ERP recordings were obtained from 91% of HCS and 91% of SZ patients. Highly significant MMN (d=0.96) and P3a (d=0.93) amplitude reductions were observed in SZ patients, comparable in magnitude to those observed in single-lab studies with no appreciable differences across laboratories. Demographic characteristics accounted for 26% and 18% of the variance in MMN and P3a amplitudes, respectively. Significant relationships were observed among demographically-adjusted MMN and P3a measures and medication status as well as several clinical, cognitive, and functional characteristics of the SZ patients. This study demonstrates that MMN and P3a ERP biomarkers can be feasibly used in multi-site clinical studies. As with many clinical tests of brain function, demographic factors contribute to MMN and P3a amplitudes and should be carefully considered in future biomarker-informed clinical studies.

Verbal working memory in schizophrenia from the Consortium on the Genetics of Schizophrenia (COGS) Study: The moderating role of smoking status and antipsychotic medications

ObjectivesWorking memory impairment has been extensively studied in schizophrenia, but less is known about moderators of the impairment. Using the Consortium on the Genetics of Schizophrenia case-control study (COGS-2), we examined smoking status, types of antipsychotic medication, and history of substance as moderators for working memory impairment in schizophrenia. MethodsFrom 5 sites, 1377 patients with schizophrenia or schizoaffective, depressed type and 1037 healthy controls completed the letter–number span (LNS) task. The LNS uses intermixed letter and digit stimuli that increase from 2 up to 8 stimuli. In the forward condition, participants repeated the letters and numbers in the order they were presented. In the reorder condition, participants repeated the digits in ascending order followed by letters in alphabetical order. ResultsSchizophrenia patients performed more poorly than controls, with a larger difference on reorder than forward conditions. Deficits were associated with symptoms, functional capacity, and functional outcome. Patients who smoked showed larger impairment than nonsmoking patients, primarily due to deficits on the reorder condition. The impairing association of smoking was more pronounced among patients taking first-generation than those taking second-generation antipsychotic medications. Correlations between working memory and community functioning were stronger for nonsmokers. History of substance use did not moderate working memory impairment. ConclusionsResults confirm the working memory impairment in schizophrenia, and indicate smoking status as an important moderator for these deficits. The greater impairment in smokers may reflect added burden of smoking on general health or that patients with greater deficits are more likely to smoke.

Is There an Association between Advanced Paternal Age and Endophenotype Deficit Levels in Schizophrenia?

The children of older fathers have increased risks of developing schizophrenia spectrum disorders, and among those who develop these disorders, those with older fathers present with more severe clinical symptoms. However, the influence of advanced paternal age on other important domains related to schizophrenia, such as quantitative endophenotype deficit levels, remains unknown. This study investigated the associations between paternal age and level of endophenotypic impairment in a well-characterized family-based sample from the Consortium on the Genetics of Schizophrenia (COGS). All families included at least one affected subject and one unaffected sibling. Subjects met criteria for schizophrenia (probands; n = 293) or were unaffected first-degree siblings of those probands (n = 382). Paternal age at the time of subjects’ birth was documented. Subjects completed a comprehensive clinical assessment and a battery of tests that measured 16 endophenotypes. After controlling for covariates, potential paternal age–endophenotype associations were analyzed using one model that included probands alone and a second model that included both probands and unaffected siblings. Endophenotype deficits in the Identical Pairs version of the 4-digit Continuous Performance Test and in the Penn Computerized Neurocognitive Battery verbal memory test showed significant associations with paternal age. However, after correcting for multiple comparisons, no endophenotype was significantly associated with paternal age. These findings suggest that factors other than advanced paternal age at birth may account for endophenotypic deficit levels in schizophrenia.

Molecular Etiologies of Schizophrenia: Are We Almost There Yet?

Molecular Etiologies of Schizophrenia: Are We Almost There Yet?

Group and site differences on the California Verbal Learning Test in persons with schizophrenia and their first-degree relatives: Findings from the Consortium on the Genetics of Schizophrenia (COGS)

Genetic studies of schizophrenia focus increasingly on putative endophenotypes because their genetic etiology may be simpler than clinical diagnosis. The Consortium on the Genetics of Schizophrenia (COGS), a multisite family study, aims to identify the genetic basis of several endophenotypes including verbal declarative memory (VDM), a neurocognitive function that shows robust impairment in schizophrenia. We present data on one type of measure of VDM, the California Verbal Learning Test, Second Edition (CVLT-II), in schizophrenia probands (n = 305), their full biological siblings (n = 449) and parents (n = 232), and in community comparison subjects (CCS; n = 509) across seven sites. Probands performed more poorly on each of five CVLT-II measures compared to related sibling and parent groups and CCS. Siblings and parents performed significantly worse than CCS on one measure (Discriminability), but with smaller effect sizes and less impairment than observed previously. The results raise questions about the homogeneity of VDM as an endophenotype, about methodological issues related to sampling, and about psychometric issues that impact the utility of the CVLT for detecting VDM deficits in nonpsychotic relatives of persons with schizophrenia.

Inhibition of the P50 cerebral evoked response to repeated auditory stimuli: Results from the Consortium on Genetics of Schizophrenia

Inhibition of the P50 evoked electroencephalographic response to the second of paired auditory stimuli has been frequently examined as a neurophysiological deficit in schizophrenia. The Consortium on the Genetics of Schizophrenia (COGS), a 7-site study funded by the National Institute of Mental Health, examined this endophenotype in recordings from 181 probands with schizophrenia, 429 of their first degree relatives, and 333 community comparison control subjects. Most probands were treated with second generation antipsychotic medications. Highly significant differences in P50 inhibition, measured as either the ratio of amplitudes or their difference in response to the two stimuli, were found between the probands and the community comparison sample. There were no differences between the COGS sites for these findings. For the ratio parameter, an admixture analysis found that nearly 40% of the relatives demonstrated deficiencies in P50 inhibition that are comparable to the deficit found in the probands. These results indicate that P50 auditory evoked potentials can be recorded across multiple sites and reliably demonstrate a physiological abnormality in schizophrenia. The appearance of the physiological abnormality in a substantial proportion of clinically unaffected first degree relatives is consistent with the hypothesis that deficits in cerebral inhibition are a familial neurobiological risk factor for the illness.

Antisaccade performance in schizophrenia patients, their first-degree biological relatives, and community comparison subjects: Data from the COGS study

The antisaccade task is a widely used technique to measure failure of inhibition, an important cause of cognitive and clinical abnormalities found in schizophrenia. Although antisaccade performance, which reflects the ability to inhibit prepotent responses, is a putative schizophrenia endophenotype, researchers have not consistently reported the expected differences between first-degree relatives and comparison groups. Schizophrenia participants (n=219) from the large Consortium on the Genetics of Schizophrenia (COGS) sample (n=1078) demonstrated significant deficits on an overlap version of the antisaccade task compared to their first-degree relatives (n=443) and community comparison subjects (CCS; n=416). Although mean antisaccade performance of first-degree relatives was intermediate between schizophrenia participants and CCS, a linear mixed-effects model adjusting for group, site, age, and gender found no significant performance differences between the first-degree relatives and CCS. However, admixture analyses showed that two components best explained the distributions in all three groups, suggesting two distinct doses of an etiological factor. Given the significant heritability of antisaccade performance, the effects of a genetic polymorphism is one possible explanation of our results.

Abnormal Auditory N100 Amplitude: A Heritable Endophenotype in First-Degree Relatives of Schizophrenia Probands

N100 evoked potential amplitude and gating abnormalities have been widely observed in schizophrenia patients. However, previous studies have been inconclusive as to whether similar deficits are present in unaffected family members. The Consortium on the Genetics of Schizophrenia (COGS) is a multisite National Institute of Mental Health (NIMH) initiative examining neurocognitive and neurophysiological measures as endophenotypes for genetic studies of schizophrenia. We report initial results from the COGS dataset of auditory N100 amplitude and gating as candidate endophenotypes. Evoked potential data were acquired from 142 schizophrenia probands, 373 unaffected first-degree relatives, and 221 community comparison subjects (CCS), using an auditory paired-click stimulation paradigm. Amplitude of the N100 response to each click and the click 2/click 1 ratio were dependent variables. Heritability was estimated based on kinships using Solar v.2.1.2. Group differences were examined after subjects were categorized as either "broad" or "narrow," based on the presence (broad) or absence (narrow) of nonpsychotic psychiatric comorbidity. Heritability estimates were .40 and .29 for click1 and click2 amplitudes and .22 for the ratio. Broad and narrow patients both had impaired click 1 amplitudes. Broad relatives, but not narrow relatives, exhibited similar impairments. There were no group differences for either click 2 amplitude or the gating ratio. N100 amplitude is a heritable measure that is abnormal in patients and a subset of relatives for whom psychiatric comorbidity may be a genetically associated phenotype. Auditory N100 gating, although heritable, is less viable as a schizophrenia endophenotype.