Deficient prepulse inhibition in schizophrenia detected by the multi-site COGS

Sexually dimorphic deficits of prepulse inhibition in patients with major depressive disorder and their relationship to symptoms: A large single ethnicity study

BACKGROUND

Sensorimotor gating deficits as measured by prepulse inhibition (PPI) of acoustic startle reflex have been repeatedly observed in patients with schizophrenia. However, studies investigating PPI in patients with major depressive disorder (MDD) are scarce, and this issue remains to be elucidated.

METHODS

Subjects were 221 patients with MDD and 250 age-matched healthy comparison subjects. Depressive symptoms were assessed by the 21-item version of the Hamilton Depression Rating Scale (HAM-D21), and the scores were divided into six factors. Thirty-five trials of startle reflex to pulse alone and pulse with prepulse were measured by electromyography. Startle magnitude, habituation, and PPI were compared between patients and comparisons stratified by sex. Relationships of startle measures to symptoms and antidepressant medication were assessed.

RESULTS

Male patients showed significantly reduced PPI compared to male comparisons, while no significant PPI difference was found between female patients and comparisons. HAM-D21 total score and several subscales were significantly correlated with PPI only in male patients. The effect of antidepressant medication was not significant for either male or female patients.

LIMITATIONS

Possible effects of the menstrual cycle could not be excluded among female subjects.

CONCLUSIONS

These findings suggest that male patients with MDD show sensorimotor gating deficits in a state-dependent manner. However, we obtained no evidence for such abnormalities in female patients with MDD.

The prolyl oligopeptidase inhibitor IPR19 ameliorates cognitive deficits in mouse models of schizophrenia

Cognitive deficits are considered a key feature of schizophrenia, and they usually precede the onset of the illness and continue after psychotic symptoms appear. Current antipsychotic drugs have little or no effect on the cognitive deficits of this disorder. Prolyl oligopeptidase (POP) is an 81-kDa monomeric serine protease that is expressed in brain and other tissues. POP inhibitors have shown neuroprotective, anti-amnesic and cognition-enhancing properties. Here we studied the potential of IPR19, a new POP inhibitor, for the treatment of the cognitive symptoms related to schizophrenia. The efficacy of the inhibitor was evaluated in mouse models based on subchronic phencyclidine and acute dizocilpine administration, and in adult offspring from mothers with immune reaction induced by polyinosinic:polycytidylic acid administration during pregnancy. Acute IPR19 administration (5mg/kg, i.p.) reversed the cognitive performance deficits of the three mouse models in the novel object recognition test, T-maze, and eight-arm radial maze. The compound also ameliorates deficits of the prepulse inhibition response. The in vitro inhibitory efficacy and selectivity, brain penetration and exposure time after injection of IPR19 were also addressed. Our results indicate that the inhibition of POP using IPR19 may offer a promising strategy to develop drugs to ameliorate the cognitive deficits of schizophrenia.

Sensorimotor gating in healthy adults tested over a 15 year period

BACKGROUND

Prepulse inhibition (PPI) of startle, an operational measure of sensorimotor gating, is used to study normal and pathological brain function. From 2001 to 2016, we screened healthy subjects (HS) to establish their suitability for tests of drug effects on PPI. Because of the size and systematic characterization of this sample across variables of relevance to PPI, we now report these screening results.

METHODS

Acoustic startle and PPI were assessed in HS to identify those eligible for studies of drug effects on PPI from 2001 to 2016, yielding 457 "eligible" subjects.

RESULTS

Data confirmed the consistency of PPI across this 15-year period, and supported the role of several variables previously reported to moderate either startle or PPI.

CONCLUSIONS

Startle and PPI are robust physiological measures that are predictably moderated by specific physiological variables in healthy adults. As such, these measures serve as robust markers of neurobiological processes in healthy and patient populations.

Using hiPSCs to model neuropsychiatric copy number variations (CNVs) has potential to reveal underlying disease mechanisms

Schizophrenia is a neuropsychological disorder with a strong heritable component; genetic risk for schizophrenia is conferred by both common variants of relatively small effect and rare variants with high penetrance. Genetically engineered mouse models can recapitulate rare variants, displaying some behavioral defects associated with schizophrenia; however, these mouse models cannot recapitulate the full genetic architecture underlying the disorder. Patient-derived human induced pluripotent stem cells (hiPSCs) present an alternative approach for studying rare variants, in the context of all other risk alleles. Genome editing technologies, such as CRISPR-Cas9, enable the generation of isogenic hiPSC lines with which to examine the functional contribution of single variants within any genetic background. Studies of these rare variants using hiPSCs have the potential to identify commonly disrupted pathways in schizophrenia and allow for the identification of new therapeutic targets. This article is part of a Special Issue entitled SI:StemsCellsinPsychiatry.

Deictic and Propositional Meaning-New Perspectives on Language in Schizophrenia

Emerging linguistic evidence points at disordered language behavior as a defining characteristic of schizophrenia. In this article, we review this literature and demonstrate how a framework focusing on two core functions of language-reference and propositional meaning-can conceptualize schizophrenic symptoms, identify important variables for risk assessment, diagnosis, and treatment, and inform cognitive behavioral therapy and other remedial approaches. We introduce the linguistic phenomena of deictic anchoring and propositional complexity, explain how they relate to schizophrenic symptoms, and show how they can be tracked in language behavior.

Endophenotype best practices

This review examines the current state of electrophysiological endophenotype research and recommends best practices that are based on knowledge gleaned from the last decade of molecular genetic research with complex traits. Endophenotype research is being oversold for its potential to help discover psychopathology relevant genes using the types of small samples feasible for electrophysiological research. This is largely because the genetic architecture of endophenotypes appears to be very much like that of behavioral traits and disorders: they are complex, influenced by many variants (e.g., tens of thousands) within many genes, each contributing a very small effect. Out of over 40 electrophysiological endophenotypes covered by our review, only resting heart, a measure that has received scant advocacy as an endophenotype, emerges as an electrophysiological variable with verified associations with molecular genetic variants. To move the field forward, investigations designed to discover novel variants associated with endophenotypes will need extremely large samples best obtained by forming consortia and sharing data obtained from genome wide arrays. In addition, endophenotype research can benefit from successful molecular genetic studies of psychopathology by examining the degree to which these verified psychopathology-relevant variants are also associated with an endophenotype, and by using knowledge about the functional significance of these variants to generate new endophenotypes. Even without molecular genetic associations, endophenotypes still have value in studying the development of disorders in unaffected individuals at high genetic risk, constructing animal models, and gaining insight into neural mechanisms that are relevant to clinical disorder.

Sensorimotor gating of the startle reflex: what we said 25 years ago, what has happened since then, and what comes next

Our 1992 paper, 'The neural substrates of sensorimotor gating of the startle reflex: a review of recent findings and their implications', reviewed a series of (then) new and preliminary findings from cross-species studies of prepulse inhibition of the startle reflex, and commented on their implications. At the time that the report was composed, PubMed listed about 40 citations for studies using the search term 'prepulse inhibition'. In the ensuing 25 years, the field has added about 2700 such reports, reflecting the substantial growth in interest in prepulse inhibition and its utility across a number of different experimental applications. The 30th anniversary of the Journal of Psychopharmacology provides an opportunity to comment briefly on what was described in that 1992 report, how the field has progressed in the subsequent decades, and the paths forward for studies of prepulse inhibition and its use as an operational measure of sensorimotor gating. Among these future paths, we highlight the use of prepulse inhibition as: an endophenotype for genomic studies, and a biomarker for healthy brain circuitry, which may predict sensitivity to psychotherapeutics. Our 1992 report was highly speculative and based on paper-thin empirical data, yet viewed in a certain light, it appears to have contained a basic roadmap for a journey spanning the next 25 years of prepulse inhibition research… and 'what a long, strange trip it's been'.

A large single ethnicity study of prepulse inhibition in schizophrenia: Separate analysis by sex focusing on effect of symptoms

Deficits in sensorimotor gating, as measured with prepulse inhibition (PPI), have been considered an endophenotype of schizophrenia. However, the question remains whether these deficits are related to current symptoms. This single site study aimed to explore clinical features related to the modulation of startle reflex in a large sample of Japanese patients with schizophrenia (DSM-IV). The subjects comprised 181 patients and 250 healthy controls matched for age and sex. Schizophrenia symptoms were assessed with the Positive and Negative Syndrome Scale (PANSS). Startle reflex to acoustic stimuli was recorded using a startle stimulus of 115 dB and a prepulse of four different conditions (intensity: 86 dB or 90 dB; lead interval: 60 ms or 120 ms). Patients exhibited significantly reduced startle magnitude (p < 0.001), habituation (p = 0.001), and PPI (90 dB, 60 ms, p = 0.016; 90 dB, 120 ms, p = 0.001) compared with controls. Patients of both sexes exhibited significantly lower habituation and PPI (90 dB, 120 ms) compared with the same sex controls. We could not detect a significant correlation with any clinical variable in the entire patients, however, when men and women were examined separately, there was a negative correlation with the PANSS cognitive domain (ρ = -0.33, p = 0.008) in men, but not in women. Moreover, when patients were subdivided into four clusters, two clusters with high positive symptoms showed significant PPI deficits in men. Our results suggest that sensorimotor gating is impaired in schizophrenia of both sexes, and PPI deficits may be related to thought disturbance and disorganization in male patients with schizophrenia.

Prepulse inhibition in euthymic bipolar disorder patients in comparison with control subjects

OBJECTIVE

Deficient prepulse inhibition (PPI) of the startle response, indicating sensorimotor gating deficits, has been reported in schizophrenia and other neuropsychiatric disorders. This study aimed to assess sensorimotor gating deficits in patients with euthymic bipolar. Furthermore, we analysed the relationships between PPI and clinical and cognitive measures.

METHOD

Prepulse inhibition was measured in 64 patients with euthymic bipolar and in 64 control subjects matched for age, gender, education level and smoking status. Clinical characteristics and level of functioning were assessed in all participants using Hamilton Depression Rating Scale (HDRS), Young Mania Rating Scale (YMRS) and Functioning Assessment Short Test (FAST). Cognition was evaluated using the Measurement and Treatment Research to Improve Cognition in Schizophrenia Consensus Cognitive Battery (MCCB) and the Stroop test as an additional measure of executive function.

RESULTS

Compared with controls, patients with bipolar disorder exhibited PPI deficits at 60- and 120-millisecond prepulse-pulse intervals. Among patients with bipolar disorder, PPI was correlated with the social cognition domain of the MCCB. PPI was not significantly correlated with other clinical, functional and neurocognitive variables in either group.

CONCLUSIONS

Our data suggest that PPI deficit is a neurobiological marker in euthymic bipolar disorder, which is associated with social cognition but not with other clinical, functional or cognitive measures.

The Relationship of Common Risk Variants and Polygenic Risk for Schizophrenia to Sensorimotor Gating

BACKGROUND

Prepulse inhibition (PPI) of the startle reflex has been suggested as a candidate endophenotype for schizophrenia research, as it shows high heritability and has been found deficient in schizophrenia spectrum disorders. The objectives of the study were to 1) identify common genetic variants associated with baseline startle and PPI; 2) estimate the single nucleotide polymorphism heritability; and 3) examine the relationship of polygenic score for schizophrenia with baseline startle and PPI.

METHODS

A cohort of healthy young male subjects (n = 1493) originating from the Learning on Genetics of Schizophrenia Spectrum project was assessed for baseline startle and PPI. The most recent genome-wide association study in schizophrenia from the Psychiatric Genomics Consortium 2 was used to calculate polygenic scores.

RESULTS

Eleven loci showed suggestive association (p < 10(-6)) with baseline startle and PPI in the discovery cohort. Additional genotyping in a replication cohort identified genome-wide significant association at two loci (rs61810702 and rs4718984). These loci were co-localized with expression quantitative trait loci associated with gene expression of nerve growth factor (NGF) and calneuron 1 (CALN1) genes. Estimation of the genetic and environmental contributions to baseline startle and PPI showed a substantial single nucleotide polymorphism heritability for 120-ms PPI stimuli. Increased polygenic risk score for schizophrenia was associated with reduced PPI.

CONCLUSIONS

Common genetic variation has an important role in the etiology of schizophrenia and PPI impairments. Overall, these data support the idea that PPI is a valid endophenotype that can be used to explore the genetic architecture of schizophrenia.

Paternal age effect: Replication in schizophrenia with intriguing dissociation between bipolar with and without psychosis

Advanced paternal age (APA) is a risk factor for schizophrenia (Sz) and bipolar disorder (BP). Putative mechanisms include heritable genetic factors, de novo mutations, and epigenetic mechanisms. Few studies have explored phenotypic features associated with APA. The Genomic Psychiatry Cohort established a clinically characterized repository of genomic samples from subjects with a Sz-BP diagnosis or unaffected controls, 12,975 with parental age information. We estimated relative risk ratios for Sz, schizoaffective depressed and bipolar types (SA-D, SA-B), and BP with and without history of psychotic features (PF) relative to the control group, comparing each paternal age group to the reference group 20-24 years. All tests were two-sided with adjustment for multiple comparisons. Subjects with fathers age 45+ had significantly higher risk for all diagnoses except for BP w/o PF. APA also bore no significant relation to family psychiatric history. In conclusion, we replicated APA as a risk factor for Sz. To our knowledge, this is the first published report of APA in a BP sample stratified by psychosis history, extending this association only in BP w/PF. This suggests that phenotypic expression of the APA effect in Sz-BP spectrum is psychosis, per se, rather than other aspects of these complex disorders. The lack of a significant relationship between paternal age and familial disease patterns suggests that underlying mechanisms of the paternal age effect may involve a complex interaction of heritable and non-heritable factors. The authors discuss implications and testable hypotheses, starting with a focus on genetic mechanisms and endophenotypic expressions of dopaminergic function. © 2015 Wiley Periodicals, Inc.

Sleep duration, depression, and oxytocinergic genotype influence prepulse inhibition of the startle reflex in postpartum women

The postpartum period is characterized by a post-withdrawal hormonal status, sleep deprivation, and susceptibility to affective disorders. Postpartum mothering involves automatic and attentional processes to screen out new external as well as internal stimuli. The present study investigated sensorimotor gating in relation to sleep duration, depression, as well as catecholaminergic and oxytocinergic genotypes in postpartum women. Prepulse inhibition (PPI) of the startle reflex and startle reactivity were assessed two months postpartum in 141 healthy and 29 depressed women. The catechol-O-methyltransferase (COMT) Val158Met, and oxytocin receptor (OXTR) rs237885 and rs53576 polymorphisms were genotyped, and data on sleep duration were collected. Short sleep duration (less than four hours in the preceding night) and postpartum depression were independently associated with lower PPI. Also, women with postpartum depression had higher startle reactivity in comparison with controls. The OXTR rs237885 genotype was related to PPI in an allele dose-dependent mode, with T/T healthy postpartum women carriers displaying the lowest PPI. Reduced sensorimotor gating was associated with sleep deprivation and depressive symptoms during the postpartum period. Individual neurophysiological vulnerability might be mediated by oxytocinergic genotype which relates to bonding and stress response. These findings implicate the putative relevance of lower PPI of the startle response as an objective physiological correlate of liability to postpartum depression.

Sex and age specific effects of delta-9-tetrahydrocannabinol during the periadolescent period in the rat: The unique susceptibility of the prepubescent animal

Adolescents who use marijuana are more likely to exhibit anxiety, depression, and other mood disorders, including psychotic-like symptoms. Additionally, the age at onset of use and the stress history of the individual can affect responses to cannabis. To examine the effect of early life experience on adolescent Δ-9-tetrahydrocannabinol (THC) exposure, we exposed adolescent (postnatal day (P) 29-38) male and female rats, either shipped from a supplier or born in our vivarium, to once daily injections of 3mg/kg THC. Our findings suggest that males are more sensitive to the anxiolytic and antidepressant effects of THC, as measured by the elevated plus maze (EPM) and forced swim test (FST), respectively, than females. Exposure to the FST increased plasma corticosterone levels, regardless of drug treatment or origin and females had higher levels than males overall. Shipping increased THC responses in females (acoustic startle habituation) and in males (latency to immobility in FST). No significant effects of THC or shipping on pre-pulse inhibition were observed. Due to differences in timing of puberty in males and females during the P29-38 period of THC treatment, we also dosed female rats between P21-30 (pre-puberty) and male rats between P39-48 (puberty). Pre-pubertal animals showed reductions in anxiety on the EPM, an effect that was not seen in animals treated during puberty. These results suggest that both sexes are more susceptible to changes in emotional behavior when THC exposure occurs just prior to the onset of puberty. Within the animals dosed from P29-38, THC increased cannabinoid receptor 1 (CB1R) mRNA expression and tended to decrease CP55,940 stimulated [³⁵S]GTPγS binding in the central amygdala only of females. Therefore, early stress enhances THC responses in males (in FST) and females (ASR habituation), THC alters CB1R expression and function in females only and prepubescent rats are generally more responsive to THC than pubertal rats. In summary, THC and stress interact with the developing endocannabinoid system in a sex specific manner during the peri-pubertal period.

Memantine Effects On Sensorimotor Gating and Mismatch Negativity in Patients with Chronic Psychosis

Patients with chronic psychotic disorders (CPD) exhibit deficient sensorimotor gating (measured by prepulse inhibition (PPI) of startle) and mismatch negativity (MMN). In healthy subjects (HS), N-methyl-D-aspartate (NMDA) antagonists like memantine and ketamine increase PPI, and under some conditions, memantine enhances MMN; these findings present a challenge to understanding the basis for deficient PPI and MMN in psychotic disorders, as reduced NMDA activity is implicated in the pathogenesis of these disorders. Here we assessed for the first time the effects of memantine on PPI and MMN in CPD subjects. Baseline PPI was measured in HS and patients with a diagnosis of schizophrenia or schizoaffective disorder, depressed type. Subjects (total n=84) were then tested twice, in a double-blind crossover design, comparing either: (1) placebo vs 10 mg of memantine or (2) placebo vs 20 mg memantine. Tests included measures of acoustic startle magnitude and habituation, PPI, MMN, autonomic indices, and subjective self-rating scales. Memantine (20 mg) significantly enhanced PPI in CPD subjects, and enhanced MMN across subject groups. These effects on PPI were age dependent and most evident in older CPD patients, whereas those on MMN were most evident in younger subjects. The lower dose (10 mg) either had no detectable effect or tended to degrade these measures. The NMDA antagonist, memantine, has dose-dependent effects on preconscious, automatic measures of sensorimotor gating and auditory sensory processing that are associated with enhanced cognition and function in CPD patients. Ongoing studies will determine whether these memantine-induced changes predict acute pro-cognitive or otherwise clinically beneficial effects in CPD patients.

Variants Near CCK Receptors are Associated With Electrophysiological Responses to Pre-pulse Startle Stimuli in a Mexican American Cohort

Neurophysiological measurements of the response to pre-pulse and startle stimuli have been suggested to represent an important endophenotype for both substance dependence and other select psychiatric disorders. We have previously shown, in young adult Mexican Americans (MA), that presentation of a short delay acoustic pre-pulse, prior to the startle stimuli can elicit a late negative component at about 400 msec (N4S), in the event-related potential (ERP), recorded from frontal cortical areas. In the present study, we investigated whether genetic factors associated with this endophenotype could be identified. The study included 420 (age 18-30 years) MA men (n = 170), and women (n = 250). DNA was genotyped using an Affymetrix Axiom Exome1A chip. An association analysis revealed that the CCKAR and CCKBR (cholecystokinin A and B receptor) genes each had a nearby variant that showed suggestive significance with the amplitude of the N4S component to pre-pulse stimuli. The neurotransmitter cholecystokinin (CCK), along with its receptors, CCKAR and CCKBR, have been previously associated with psychiatric disorders, suggesting that variants near these genes may play a role in the pre-pulse/startle response in this cohort.

Neurobiological background of negative symptoms

Studies investigating neurobiological bases of negative symptoms of schizophrenia failed to provide consistent findings, possibly due to the heterogeneity of this psychopathological construct. We tried to review the findings published to date investigating neurobiological abnormalities after reducing the heterogeneity of the negative symptoms construct. The literature in electronic databases as well as citations and major articles are reviewed with respect to the phenomenology, pathology, genetics and neurobiology of schizophrenia. We searched PubMed with the keywords "negative symptoms," "deficit schizophrenia," "persistent negative symptoms," "neurotransmissions," "neuroimaging" and "genetic." Additional articles were identified by manually checking the reference lists of the relevant publications. Publications in English were considered, and unpublished studies, conference abstracts and poster presentations were not included. Structural and functional imaging studies addressed the issue of neurobiological background of negative symptoms from several perspectives (considering them as a unitary construct, focusing on primary and/or persistent negative symptoms and, more recently, clustering them into factors), but produced discrepant findings. The examined studies provided evidence suggesting that even primary and persistent negative symptoms include different psychopathological constructs, probably reflecting the dysfunction of different neurobiological substrates. Furthermore, they suggest that complex alterations in multiple neurotransmitter systems and genetic variants might influence the expression of negative symptoms in schizophrenia. On the whole, the reviewed findings, representing the distillation of a large body of disparate data, suggest that further deconstruction of negative symptomatology into more elementary components is needed to gain insight into underlying neurobiological mechanisms.

Supraphysiological hormonal status, anxiety disorders, and COMT Val/Val genotype are associated with reduced sensorimotor gating in women

Pregnancy is a period characterized by a supraphysiological hormonal status, and greater anxiety proneness, which can lead to peripartum affective symptoms with dramatic consequences not only for the woman but also for the child. Clinical psychiatry is heavily hampered by the paucity of objective and biology-based intermediate phenotypes. Prepulse inhibition (PPI) of the startle response, a neurophysiological measure of sensorimotor gating, has been poorly investigated in relation to anxiety and in pregnant women. In the present study, the PPI of healthy non-pregnant women (n = 82) and late pregnant women (n = 217) was investigated. Age, BMI, depression and anxiety symptoms, tobacco use, and antidepressant medication were considered. We investigated and provided evidence of lower PPI: (i) in healthy pregnant women compared to healthy non-pregnant controls, (ii) in pregnant women with anxiety disorders compared to healthy pregnant women, (iii) in pregnant women with anxiety disorders using SSRI compared to un-medicated pregnant women with anxiety disorders, and (iv) in healthy pregnant women carrying the COMT Val158Met Val/Val genotype compared to Met carriers. Altogether, a reduced sensorimotor gating as an effect of supraphysiological hormonal status, anxiety disorders, SSRIs, and catecholaminergic genotype, implicate the putative relevance of lower PPI as an objective biological correlate of anxiety proneness in pregnant women. These findings call for prospective studies to dissect the multifactorial influences on PPI in relation to mental health of pregnant women.

Diametrical diseases reflect evolutionary-genetic tradeoffs: Evidence from psychiatry, neurology, rheumatology, oncology and immunology

Tradeoffs centrally mediate the expression of human adaptations. We propose that tradeoffs also influence the prevalence and forms of human maladaptation manifest in disease. By this logic, increased risk for one set of diseases commonly engenders decreased risk for another, diametric, set of diseases. We describe evidence for such diametric sets of diseases from epidemiological, genetic and molecular studies in four clinical domains: (i) psychiatry (autism vs psychotic-affective conditions), (ii) rheumatology (osteoarthritis vs osteoporosis), (iii) oncology and neurology (cancer vs neurodegenerative disorders) and (iv) immunology (autoimmunity vs infectious disease). Diametric disorders are important to recognize because genotypes or environmental factors that increase risk for one set of disorders protect from opposite disorders, thereby providing novel and direct insights into disease causes, prevention and therapy. Ascertaining the mechanisms that underlie disease-related tradeoffs should also indicate means of circumventing or alleviating them, and thus reducing the incidence and impacts of human disease in a more general way.

Future clinical uses of neurophysiological biomarkers to predict and monitor treatment response for schizophrenia

Advances in psychiatric neuroscience have transformed our understanding of impaired and spared brain functions in psychotic illnesses. Despite substantial progress, few (if any) laboratory tests have graduated to clinics to inform diagnoses, guide treatments, and monitor treatment response. Providers must rely on careful behavioral observation and interview techniques to make inferences about patients' inner experiences and then secondary deductions about impacted neural systems. Development of more effective treatments has also been hindered by a lack of translational quantitative biomarkers that can span the brain-behavior treatment knowledge gap. Here, we describe an example of a simple, low-cost, and translatable electroencephalography (EEG) measure that offers promise for improving our understanding and treatment of psychotic illnesses: mismatch negativity (MMN). MMN is sensitive to and/or predicts response to some pharmacologic and nonpharmacologic interventions and accounts for substantial portions of variance in clinical, cognitive, and psychosocial functioning in schizophrenia (SZ). This measure has recently been validated for use in large-scale multisite clinical studies of SZ. Finally, MMN greatly improves our ability to forecast which individuals at high clinical risk actually develop a psychotic illness. These attributes suggest that MMN can contribute to personalized biomarker-guided treatment strategies aimed at ameliorating or even preventing the onset of psychosis.

Consortium on the Genetics of Schizophrenia (COGS) assessment of endophenotypes for schizophrenia: an introduction to this Special Issue of Schizophrenia Research

BACKGROUND

The COGS is a multi-site NIMH-sponsored investigation of the genetic basis of 12 primary and multiple secondary quantitative endophenotypes in schizophrenia.

METHODS

Since 2003, COGS has completed studies using a family-based ascertainment strategy (COGS-1), and a case-control ascertainment strategy (COGS-2) (cumulative "n">4000).

RESULTS

COGS-1 family study confirmed robust deficits in, and heritability of, these endophenotypes in schizophrenia, and provided evidence for a coherent genetic architecture underlying the risk for neurocognitive and neurophysiological deficits in this disorder. COGS-2 case-control findings, many reported herein, establish a foundation for fine genomic mapping and other analyses of these endophenotypes and risk genes for SZ. Several reports in this Special Issue compare findings of endophenotype deficits generated by fundamentally different COGS-1 vs. COGS-2 ascertainment strategies. Despite the expectation that family-based and case-control designs would establish demographically and potentially biologically distinct patient cohorts, findings generally revealed comparable patterns of endophenotype deficits across studies. The COGS-2 case-control design facilitated the accrual of a larger "n", permitting detailed analyses of factors moderating endophenotype performance. Some COGS-2 endophenotypes not assessed in COGS-1 are also reported, as is a new factor analytic strategy for identifying shared vs. unique factors among the COGS endophenotypes which can be used to develop composite variables with distinct genetic signatures.

DISCUSSION

The path to date of COGS-1 endophenotype and genetic findings, followed by replication and extension in COGS-2, establishes benchmarks for endophenotype deficits in SZ and their moderation by specific factors, and clear expectations for informative findings from upcoming COGS-2 genetic analyses.

The importance of endophenotypes in schizophrenia research

Endophenotypes provide a powerful neurobiological platform from which we can understand the genomic and neural substrates of schizophrenia and other common complex neuropsychiatric disorders. The Consortium on the Genetics of Schizophrenia (COGS) has conducted multisite studies on carefully selected key neurocognitive and neurophysiological endophenotypes in 300 families (COGS-1) and then in a follow up multisite case-control study of 2471 subjects (COGS-2). Endophenotypes are neurobiologically informed quantitative measures that show deficits in probands and their first degree relatives. They are more amenable to statistical analysis than are "fuzzy" qualitative clinical traits or confoundingly heterogeneous diagnostic categories. Endophenotypes are also viewed as uniquely informative in traditional diagnosis-based as well as emerging NIMH Research Domain (RDoC) contexts, offering a bridge between the two approaches to psychopathology classification and research. Endo- or intermediate phenotypes are heritable, and in the COGS-1 cohort their level of heritability is in the same range as is the heritability of schizophrenia itself, using the same statistical methods and subjects to assess both. Because we can demonstrate endophenotypes link to both gene networks and neural circuits on the one hand and also to real-life function, endophenotypes provide a critically important bridge for "connecting the dots" between genes, cells, circuits, information processing, neurocognition and functional impairment and personalized treatment selection in schizophrenia patients. By connecting schizophrenia risk genes with neurobiologically informed endophenotypes, and via the use of association, linkage, sequencing, stem cell and other strategies, we can provide our field with new neurobiologically informed information in our efforts to understand and treat schizophrenia. Evolving views, data and new analytic strategies about schizophrenia risk, pathology and treatment are described in this Viewpoint and in the accompanying Special Issue reports.

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.

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.

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

BACKGROUND

Neurocognitive 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.

METHODS

The 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.

RESULTS

Demographically, 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.

CONCLUSIONS

Patients 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.

Future clinical uses of neurophysiological biomarkers to predict and monitor treatment response for schizophrenia

Advances in psychiatric neuroscience have transformed our understanding of impaired and spared brain functions in psychotic illnesses. Despite substantial progress, few (if any) laboratory tests have graduated to clinics to inform diagnoses, guide treatments, and monitor treatment response. Providers must rely on careful behavioral observation and interview techniques to make inferences about patients' inner experiences and then secondary deductions about impacted neural systems. Development of more effective treatments has also been hindered by a lack of translational quantitative biomarkers that can span the brain-behavior treatment knowledge gap. Here, we describe an example of a simple, low-cost, and translatable electroencephalography (EEG) measure that offers promise for improving our understanding and treatment of psychotic illnesses: mismatch negativity (MMN). MMN is sensitive to and/or predicts response to some pharmacologic and nonpharmacologic interventions and accounts for substantial portions of variance in clinical, cognitive, and psychosocial functioning in schizophrenia (SZ). This measure has recently been validated for use in large-scale multisite clinical studies of SZ. Finally, MMN greatly improves our ability to forecast which individuals at high clinical risk actually develop a psychotic illness. These attributes suggest that MMN can contribute to personalized biomarker-guided treatment strategies aimed at ameliorating or even preventing the onset of psychosis.

Animal Models of Deficient Sensorimotor Gating in Schizophrenia: Are They Still Relevant?

Animal models of impaired sensorimotor gating, as assessed by prepulse inhibition (PPI) of startle, have demonstrated clear validity at face, predictive, and construct levels for schizophrenia therapeutics, neurophysiological endophenotypes, and potential causative insults for this group of disorders. However, with the growing recognition of the heterogeneity of the schizophrenias, and the less sanguine view of the clinical value of antipsychotic (AP) medications, our field must look beyond "validity," to assess the actual utility of these models. At a substantial cost in terms of research support and intellectual capital, what has come from these models, that we can say has actually helped schizophrenia patients? Such introspection is timely, as we are reassessing not only our view of the genetic and pathophysiological diversity of these disorders, but also the predominant strategies for SZ therapeutics; indeed, our field is gaining awareness that we must move away from a "find what's broke and fix it" approach, toward identifying spared neural and cognitive function in SZ patients, and matching these residual neural assets with learning-based therapies. Perhaps, construct-valid models that identify evidence of "spared function" in neural substrates might reveal opportunities for future therapeutics and allow us to study these substrates at a mechanistic level to maximize opportunities for neuroplasticity. Such an effort will require a retooling of our models, and more importantly, a re-evaluation of their utility. For animal models to remain relevant in the search for schizophrenia therapeutics, they will need to focus less on what is valid and focus more on what is useful.

Sleep deprivation disrupts prepulse inhibition and induces psychosis-like symptoms in healthy humans

Translational biomarkers, such as prepulse inhibition (PPI) of the acoustic startle response, are playing an increasingly important role in the development of antipsychotic drugs for schizophrenia and related conditions. However, attempts to reliably induce a PPI deficit by psychotomimetic drugs have not been successful, leaving an unmet need for a cross-species psychosis model sensitive to this widely studied surrogate treatment target. Sleep deprivation (SD) might be such a model as it has previously been shown to induce PPI deficits in rats, which could be selectively prevented with antipsychotic but not anxiolytic or antidepressant compounds. Here, in a first proof-of-concept study we tested whether SD induces a deficit in PPI and an increase in psychosis-like symptoms in healthy humans. In two counterbalanced sessions, acoustic PPI and self-reported psychosis-like symptoms (Psychotomimetic States Inventory) were measured in 24 healthy human volunteers after a normal night's sleep and after a night of total SD. SD decreased PPI (p = 0.001) without affecting the magnitude or habituation of the startle response (all p > 0.13). SD also induced perceptual distortions, cognitive disorganization, and anhedonia (all p < 0.02). Thus, extending previous rodent work, we conclude that SD, in combination with the PPI biomarker, might be a promising translational surrogate model for psychosis as this method represents a possibility to partially and reversibly mimic the pathogenesis of psychotic states.

Prolonged temporal interaction for peripheral visual processing in schizophrenia: evidence from a three-flash illusion

BACKGROUND

Coherent perception of the visual world requires orderly processing of spatially and temporally distributed visual information across the visual field. The organization of this visual information is impaired in schizophrenia. We previously found that visual temporal integration in patients is prolonged, using flashes presented to the central fovea. In this study, we investigated this temporal interaction in both the fovea and fairly far out in the peripheral visual field.

METHODS

We used a 'three-flash' illusion paradigm in which two spatially-coincident light pulses (of 1 ms each) are perceived by healthy individuals as one, two or three flashes depending on the time interval between the pulses. In each trial, two light pulses were presented in the fovea or 34° out in the right visual field. The inter-stimulus pulse interval (ISI) ranged from 30 to 310 ms. The task for patients (n=28) and controls (n=26) was to indicate the number of flashes (one, two or three) perceived after each two-pulse presentation.

RESULTS

For the controls, the peak of the three-flash illusion was shifted to longer ISIs (150 ms) in the periphery compared to the fovea (110 ms). For the patients, the three-flash illusion was greater and occurred at longer ISIs (270 ms in the periphery and 190 ms at the fovea).

CONCLUSION

Compared to the central visual field, the range of temporal interactions in the periphery is prolonged to a greater extent in schizophrenia. This exacerbated temporal expansion in peripheral vision suggests a coarse temporal resolution for visual and cognitive organization in this mental disorder.

Neurophysiological biomarkers informing the clinical neuroscience of schizophrenia: mismatch negativity and prepulse inhibition of startle

With the growing recognition of the heterogeneity of major brain disorders, and particularly the schizophrenias (SZ), biomarkers are being sought that parse patient groups in ways that can be used to predict treatment response, prognosis, and pathophysiology. A primary focus to date has been to identify biomarkers that predict damage or dysfunction within brain systems in SZ patients, that could then serve as targets for interventions designed to "undo" the causative pathology. After almost 50 years as the predominant strategy for developing SZ therapeutics, evidence supporting the value of this "find what's broke and fix it" approach is lacking. Here, we suggest an alternative strategy of using biomarkers to identify evidence of spared neural and cognitive function in SZ patients, and matching these residual neural assets with therapies toward which they can be applied. We describe ways to extract and interpret evidence of "spared function," using neurocognitive, and neurophysiological measures, and, suggest that further evidence of available neuroplasticity might be gleaned from studies in which the response to drug challenges and "practice effects" are measured. Finally, we discuss examples in which "better" (more normal) performance in specific neurophysiological measures predict a positive response to a neurocognitive task or therapeutic intervention. We believe that our field stands to gain tremendous therapeutic leverage by focusing less on what is "wrong" with our patients, and instead, focusing more on what is "right".

An Overview of the Association between Schizotypy and Dopamine

Schizotypy refers to a constellation of personality traits that are believed to mirror the subclinical expression of schizophrenia in the general population. Evidence from pharmacological studies indicates that dopamine (DA) is involved in the etiology of schizophrenia. Based on the assumption of a continuum between schizophrenia and schizotypy, researchers have begun investigating the association between DA and schizotypy using a wide range of methods. In this article, we review published studies on this association from the following areas of work: (1) experimental investigations of the interactive effects of dopaminergic challenges and schizotypy on cognition, motor control, and behavior (2), dopaminergically supported cognitive functions (3), studies of associations between schizotypy and polymorphisms in genes involved in dopaminergic neurotransmission, and (4) molecular imaging studies of the association between schizotypy and markers of the DA system. Together, data from these lines of evidence suggest that DA is important to the expression and experience of schizotypy and associated behavioral biases. An important observation is that the experimental designs, methods, and manipulations used in this research are highly heterogeneous. Future studies are required to replicate individual observations, to enlighten the link between DA and different schizotypy dimensions (positive, negative, cognitive disorganization), and to guide the search for solid DA-sensitive behavioral markers. Such studies are important in order to clarify inconsistencies between studies. More work is also needed to identify differences between dopaminergic alterations in schizotypy compared to the dysfunctions observed in schizophrenia.