Brain volumes in familial and non-familial schizophrenic probands and their unaffected relatives

Psychosis Endophenotypes: A Gene-Set-Specific Polygenic Risk Score Analysis

BACKGROUND AND HYPOTHESIS

Endophenotypes can help to bridge the gap between psychosis and its genetic predispositions, but their underlying mechanisms remain largely unknown. This study aims to identify biological mechanisms that are relevant to the endophenotypes for psychosis, by partitioning polygenic risk scores into specific gene sets and testing their associations with endophenotypes.

STUDY DESIGN

We computed polygenic risk scores for schizophrenia and bipolar disorder restricted to brain-related gene sets retrieved from public databases and previous publications. Three hundred and seventy-eight gene-set-specific polygenic risk scores were generated for 4506 participants. Seven endophenotypes were also measured in the sample. Linear mixed-effects models were fitted to test associations between each endophenotype and each gene-set-specific polygenic risk score.

STUDY RESULTS

After correction for multiple testing, we found that a reduced P300 amplitude was associated with a higher schizophrenia polygenic risk score of the forebrain regionalization gene set (mean difference per SD increase in the polygenic risk score: -1.15 µV; 95% CI: -1.70 to -0.59 µV; P = 6 × 10-5). The schizophrenia polygenic risk score of forebrain regionalization also explained more variance of the P300 amplitude (R2 = 0.032) than other polygenic risk scores, including the genome-wide polygenic risk scores.

CONCLUSIONS

Our finding on reduced P300 amplitudes suggests that certain genetic variants alter early brain development thereby increasing schizophrenia risk years later. Gene-set-specific polygenic risk scores are a useful tool to elucidate biological mechanisms of psychosis and endophenotypes, offering leads for experimental validation in cellular and animal models.

Structural network alterations and their association with neurological soft signs in schizophrenia: Evidence from clinical patients and unaffected siblings

BACKGROUND

Grey matter abnormalities and neurological soft signs (NSS) have been found in schizophrenia patients and their unaffected relatives. Evidence suggested that NSS are associated with grey matter morphometrical alterations in multiple regions in schizophrenia. However, the association between NSS and structural abnormalities at network level remains largely unexplored, especially in the schizophrenia and unaffected siblings.

METHOD

We used source-based morphometry (SBM) to examine the association of structural brain network characteristics with NSS in 62 schizophrenia patients, 25 unaffected siblings, and 60 healthy controls.

RESULTS

Two components, namely the IC-5 (superior temporal gyrus, inferior frontal gyrus and insula network) and the IC-10 (parahippocampal gyrus, fusiform, thalamus and insula network) showed significant grey matter reductions in schizophrenia patients compared to healthy controls and unaffected siblings. Further association analysis demonstrated separate NSS-related grey matter covarying patterns in schizophrenia, unaffected siblings and healthy controls. Specifically, NSS were negatively associated with IC-1 (hippocampus, caudate and thalamus network) and IC-5 in schizophrenia, but with IC-3 (caudate, superior and middle frontal cortices network) in unaffected siblings and with IC-5 in healthy controls.

CONCLUSION

Our results confirmed the key cortical and subcortical network abnormalities and NSS-related grey matter covarying patterns in the schizophrenia and unaffected siblings. Our findings suggest that brain regions implicating genetic liability to schizophrenia are partly separated from brain regions implicating neural abnormalities.

Obstetric Complications and Brain Imaging in Schizophrenia: A Systematic Review

Schizophrenia is a complex disorder in which clinical symptomatology typically reflects underlying brain abnormalities that coalign with multiple physical health comorbidities. The pathogenesis of schizophrenia involves the interplay between genetic and environmental factors, with obstetric complications widely described as key players in elevating the risk of psychosis. In this regard, understanding the anatomical and functional alterations associated with obstetric complications may help to elucidate potential mechanisms through which birth complications could contribute to schizophrenia pathogenesis. We conducted a systematic review of the extant literature describing brain abnormalities and obstetric complications in patients with schizophrenia and related disorders in accordance with the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) guidelines. A total of 471 studies were retrieved and screened, and 33 studies met inclusion criteria for our review. Studies varied considerably in their methods, with 11 studies employing computed tomography, 1 using magnetic resonance spectroscopy, and 21 using magnetic resonance imaging. The scientific quality of the included studies was assessed and documented. Obstetric complications increase the risk of provoking brain abnormalities. These abnormalities range from decreased gray matter volume and abnormal brain-ventricle ratios to a reduction of volume in limbic regions-which relate to what is commonly observed in schizophrenia. However, current evidence from neuroimaging studies remains scant in relation to establishing obstetric complications as an independent risk factor for schizophrenia.

Obstetric complications in patients with schizophrenia and their unaffected siblings

Objective

We sought to explore whether obstetric complications (OCs) are more likely to occur in the presence of familial/genetic susceptibility for schizophrenia or whether they themselves represent an independent environmental risk factor for schizophrenia.

Methods

The presence of OCs was assessed through maternal interview on 216 subjects, comprising 36 patients with schizophrenia from multiply affected families, 38 of their unaffected siblings, 31 schizophrenic patients with no family history of psychosis, 51 of their unaffected siblings and 60 normal comparison subjects. We examined the familiality of OCs and whether OCs were commoner in the patient and sibling groups than in the control group.

Results

OCs tended to cluster within families, especially in multiply affected families. Patients with schizophrenia, especially those from multiply affected families, had a significantly higher rate of OCs compared to normal comparison subjects, but there was no evidence for an elevated rate of OCs in unaffected siblings.

Conclusion

Our data provides little evidence for a link between OCs and genetic susceptibility to schizophrenia. If high rates of OCs are related to schizophrenia genes, this relationship is weak and will only be detected by very large sample sizes.

Associations between psychosis endophenotypes across brain functional, structural, and cognitive domains

BACKGROUND

A range of endophenotypes characterise psychosis, however there has been limited work understanding if and how they are inter-related.

METHODS

This multi-centre study includes 8754 participants: 2212 people with a psychotic disorder, 1487 unaffected relatives of probands, and 5055 healthy controls. We investigated cognition [digit span (N = 3127), block design (N = 5491), and the Rey Auditory Verbal Learning Test (N = 3543)], electrophysiology [P300 amplitude and latency (N = 1102)], and neuroanatomy [lateral ventricular volume (N = 1721)]. We used linear regression to assess the interrelationships between endophenotypes.

RESULTS

The P300 amplitude and latency were not associated (regression coef. -0.06, 95% CI -0.12 to 0.01, p = 0.060), and P300 amplitude was positively associated with block design (coef. 0.19, 95% CI 0.10-0.28, p 0.38). All the cognitive endophenotypes were associated with each other in the expected directions (all p < 0.001). Lastly, the relationships between pairs of endophenotypes were consistent in all three participant groups, differing for some of the cognitive pairings only in the strengths of the relationships.

CONCLUSIONS

The P300 amplitude and latency are independent endophenotypes; the former indexing spatial visualisation and working memory, and the latter is hypothesised to index basic processing speed. Individuals with psychotic illnesses, their unaffected relatives, and healthy controls all show similar patterns of associations between endophenotypes, endorsing the theory of a continuum of psychosis liability across the population.

A polygenic risk score analysis of psychosis endophenotypes across brain functional, structural, and cognitive domains

This large multi-center study investigates the relationships between genetic risk for schizophrenia and bipolar disorder, and multi-modal endophenotypes for psychosis. The sample included 4,242 individuals; 1,087 patients with psychosis, 822 unaffected first-degree relatives of patients, and 2,333 controls. Endophenotypes included the P300 event-related potential (N = 515), lateral ventricular volume (N = 798), and the cognitive measures block design (N = 3,089), digit span (N = 1,437), and the Ray Auditory Verbal Learning Task (N = 2,406). Data were collected across 11 sites in Europe and Australia; all genotyping and genetic analyses were done at the same laboratory in the United Kingdom. We calculated polygenic risk scores for schizophrenia and bipolar disorder separately, and used linear regression to test whether polygenic scores influenced the endophenotypes. Results showed that higher polygenic scores for schizophrenia were associated with poorer performance on the block design task and explained 0.2% (p = 0.009) of the variance. Associations in the same direction were found for bipolar disorder scores, but this was not statistically significant at the 1% level (p = 0.02). The schizophrenia score explained 0.4% of variance in lateral ventricular volumes, the largest across all phenotypes examined, although this was not significant (p = 0.063). None of the remaining associations reached significance after correction for multiple testing (with alpha at 1%). These results indicate that common genetic variants associated with schizophrenia predict performance in spatial visualization, providing additional evidence that this measure is an endophenotype for the disorder with shared genetic risk variants. The use of endophenotypes such as this will help to characterize the effects of common genetic variation in psychosis.

Cerebellar Structural Abnormalities Associated With Cognitive Function in Patients With First-Episode Psychosis

Introduction: The fundamental role of the cerebellum in higher cognitive processing has recently been highlighted. However, inconsistent findings exist in schizophrenia with respect to the exact nature of cerebellar structural abnormalities and their associations with cognitive and clinical features. Materials and Methods: We undertook a detailed investigation of cerebellar lobular volumes in 40 patients with first-episode psychosis (FEP) and 40 healthy controls (HCs) using the spatially unbiased atlas template of the cerebellum (SUIT). We examined the functional significance of cerebellar structural abnormalities in relation to cognitive and clinical outcomes in patients. Results: We found that left cerebellar lobules VI and X volumes were lower in FEP patients, compared to HCs. Smaller left lobules VI and X volumes were associated with fewer number of categories completed on the Wisconsin Card Sorting Test (WCST) in patients. In addition, smaller left lobule X volume was related to performance delay on the Trail Making Test (TMT) Part B in patients. Conclusion: Our results demonstrate that cerebellar structural abnormalities are present at the early stage of schizophrenia. We suggest functional associations of cerebellar structural changes with non-verbal executive dysfunctions in FEP.

Neural Correlates of Enhanced Genetic Risk for Schizophrenia

Schizophrenia is a disabling psychotic disorder characterized by hallucinations, delusions, and impaired functioning in many aspects of everyday life. The established condition generally becomes manifest in early adulthood, and evidence suggests that one of the most important risk factors for developing the disorder is inherited vulnerability. The established illness has been shown to be associated with deficits in many domains of cognitive function, along with structural and functional brain abnormalities, most notably in pre-frontal and temporal lobes. However, such studies have not been able to determine the extent to which such deficits relate to the presence of a schizophrenic predisposition, the presence of symptoms, and/or medication effects. A number of research groups have therefore turned to the study of relatives of affected individuals with the aim of determining if similar cognitive deficits and brain abnormalities are also found in those with increased genetic vulnerability to the disorder. In this article, studies on such individuals are discussed. It is concluded that deficits are apparent in relatives that are similar to but less marked than those seen in patients with schizophrenia.

Animal models of gene-environment interaction in schizophrenia: A dimensional perspective

Schizophrenia has long been considered as a disorder with multifactorial origins. Recent discoveries have advanced our understanding of the genetic architecture of the disease. However, even with the increase of identified risk variants, heritability estimates suggest an important contribution of non-genetic factors. Various environmental risk factors have been proposed to play a role in the etiopathogenesis of schizophrenia. These include season of birth, maternal infections, obstetric complications, adverse events at early childhood, and drug abuse. Despite the progress in identification of genetic and environmental risk factors, we still have a limited understanding of the mechanisms whereby gene-environment interactions (G × E) operate in schizophrenia and psychoses at large. In this review we provide a critical analysis of current animal models of G × E relevant to psychotic disorders and propose that dimensional perspective will advance our understanding of the complex mechanisms of these disorders.

Family load impacts orbitofrontal volume in first-episode schizophrenia

In schizophrenia, reduced orbitofrontal cortex (OFC) volume is inconsistently reported. To investigate the impact of genetic load on OFC volume, manual MRI-tracing in 23 first-episode schizophrenia patients (FE-SZ) and 23 controls was performed. FE-SZ with genetic load showed a decrease in OFC volume compared to FE-SZ without load and controls.

Compromised small-world efficiency of structural brain networks in schizophrenic patients and their unaffected parents

Several lines of evidence suggest that efficient information integration between brain regions is disrupted in schizophrenia. Abnormalities in white matter tracts that interconnect brain regions may be directly relevant to this pathophysiological process. As a complex mental disorder with high heritability, mapping abnormalities in patients and their first-degree relatives may help to disentangle the risk factors for schizophrenia. We established a weighted network model of white matter connections using diffusion tensor imaging in 25 nuclear families with schizophrenic probands (19 patients and 41 unaffected parents) and two unrelated groups of normal controls (24 controls matched with patients and 26 controls matched with relatives). The patient group showed lower global efficiency and local efficiency. The decreased regional efficiency was localized in hubs such as the bilateral frontal cortices, bilateral anterior cingulate cortices, and left precuneus. The global efficiency was negatively correlated with cognition scores derived from a 5-factor model of schizophrenic psychopathology. We also found that unaffected parents displayed decreased regional efficiency in the right temporal cortices, left supplementary motor area, left superior temporal pole, and left thalamus. The global efficiency tended to be lower in unaffected parents. Our data suggest that (1) the global efficiency loss in neuroanatomical networks may be associated with the cognitive disturbances in schizophrenia; and (2) genetic vulnerability to schizophrenia may influence the anatomical organization of an individual's brain networks.

Effects of neonatal treatment with the TRPV1 agonist, capsaicin, on adult rat brain and behaviour

Treatment of neonatal rats with the transient receptor potential vanilloid 1 (TRPV1) channel agonist, capsaicin, produces life-long loss of sensory neurons expressing TRPV1 channels. Previously it was shown that rats treated on day 2 of life with capsaicin had behavioural hyperactivity in a novel environment at 5-7 weeks of age and brain changes reminiscent of those found in subjects with schizophrenia. The objective of the present study was to investigate brain and behavioural responses of adult rats treated as neonates with capsaicin. It was found that the brain changes found at 5-7 weeks in rats treated as neonates with capsaicin persisted into adulthood (12 weeks) but were less in older rats (16-18 weeks). Increased prepulse inhibition (PPI) of acoustic startle was found in these rats at 8 and 12 weeks of age rather than the deficit commonly found in animal models of schizophrenia. Subjects with schizophrenia also have reduced flare responses to niacin and methylnicotinate proposed to be mediated by prostaglandin D2 (PGD2). Flare responses are accompanied by cutaneous plasma extravasation. It was found that the cutaneous plasma extravasation responses to methylnicotinate and PGD2 were reduced in capsaicin-treated rats. In conclusion, several neuroanatomical changes observed in capsaicin-treated rats, as well as the reduced cutaneous plasma extravasation responses, indicate that the role of TRPV1 channels in schizophrenia is worthy of investigation.

Divergent structural brain abnormalities between different genetic subtypes of children with Prader-Willi syndrome

Background

Prader–Willi syndrome (PWS) is a complex neurogenetic disorder with symptoms that indicate not only hypothalamic, but also a global, central nervous system (CNS) dysfunction. However, little is known about developmental differences in brain structure in children with PWS. Thus, our aim was to investigate global brain morphology in children with PWS, including the comparison between different genetic subtypes of PWS. In addition, we performed exploratory cortical and subcortical focal analyses.

Methods

High resolution structural magnetic resonance images were acquired in 20 children with genetically confirmed PWS (11 children carrying a deletion (DEL), 9 children with maternal uniparental disomy (mUPD)), and compared with 11 age- and gender-matched typically developing siblings as controls. Brain morphology measures were obtained using the FreeSurfer software suite.

Results

Both children with DEL and mUPD showed smaller brainstem volume, and a trend towards smaller cortical surface area and white matter volume. Children with mUPD had enlarged lateral ventricles and larger cortical cerebrospinal fluid (CSF) volume. Further, a trend towards increased cortical thickness was found in children with mUPD. Children with DEL had a smaller cerebellum, and smaller cortical and subcortical grey matter volumes. Focal analyses revealed smaller white matter volumes in left superior and bilateral inferior frontal gyri, right cingulate cortex, and bilateral precuneus areas associated with the default mode network (DMN) in children with mUPD.

Conclusions

Children with PWS show signs of impaired brain growth. Those with mUPD show signs of early brain atrophy. In contrast, children with DEL show signs of fundamentally arrested, although not deviant brain development and presented few signs of cortical atrophy. Our results of global brain measurements suggest divergent neurodevelopmental patterns in children with DEL and mUPD.

The association of white matter volume in psychotic disorders with genotypic variation in NRG1, MOG and CNP: a voxel-based analysis in affected individuals and their unaffected relatives

We investigated the role of variation in putative psychosis genes coding for elements of the white matter system by examining the contribution of genotypic variation in three single-nucleotide polymorphisms (SNPs) neuregulin 1 (NRG1) SNP8NRG221533, myelin oligodendrocytes glycoprotein (MOG) rs2857766 and CNP (rs2070106) and one haplotype HAP(ICE) (deCODE) to white matter volume in patients with psychotic disorder and their unaffected relatives. Structural magnetic resonance imaging and blood samples for genotyping were collected on 189 participants including patients with schizophrenia (SZ) or bipolar I disorder (BDI), unaffected first-degree relatives of these patients and healthy volunteers. The association of genotypic variation with white matter volume was assessed using voxel-based morphometry in SPM5. The NRG1 SNP and the HAP(ICE) haplotype were associated with abnormal white matter volume in the BDI group in the fornix, cingulum and parahippocampal gyrus circuit. In SZ the NRG1 SNP risk allele was associated with lower white matter volume in the uncinate fasciculus (UF), right inferior longitudinal fasciculus and the anterior limb of the internal capsule. Healthy G-homozygotes of the MOG SNP had greater white matter volume in areas of the brainstem and cerebellum; this relationship was absent in those with a psychotic disorder and the unaffected relatives groups. The CNP SNP did not contribute to white matter volume variation in the diagnostic groups studied. Variation in the genes coding for structural and protective components of myelin are implicated in abnormal white matter volume in the emotion circuitry of the cingulum, fornix, parahippocampal gyrus and UF in psychotic disorders.

Stress abnormalities in individuals at risk for psychosis: a review of studies in subjects with familial risk or with "at risk" mental state

Increased sensitivity to stress is known to play an important role in the transition to first episode psychosis (FEP). Hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis, and, in general, an increased sensitivity to stress, have been hypothesised to be components of the vulnerability to psychosis, but whether these abnormalities are already present before the onset of psychosis has not yet been systematically reviewed. Here we have reviewed all studies examining psychological and biological markers of the stress response in the relatives of psychotic patients and in individuals at Ultra High Risk (UHR) for psychosis. In relatives, there is evidence of increased sensitivity to stress, as shown by increased emotional reactivity to daily life stress, increased adrenocorticotropic hormone (ACTH) in response to stress, increased pituitary volume and reduced hippocampal volume. However, evidence of increased cortisol levels is less consistent. On the other hand, subjects who experience attenuated psychotic symptoms show increased cortisol levels as well as increased pituitary and reduced hippocampal volumes. Moreover, this HPA axis hyperactivity seems to be even greater among those individuals who subsequently develop frank psychosis. In summary, an enhanced HPA axis response to stress appears to be part of the biological vulnerability to psychosis which is present prior to the onset of psychosis. A further increase in cortisol levels during the transition to FEP suggests the presence of an additive factor, possibly environmental, at this stage of the illness. Possible causes and consequences of HPA axis impairment in risk for psychosis are discussed.

A plausible model of schizophrenia must incorporate psychological and social, as well as neuro developmental, risk factors

Subtle alterations in brain development caused by genes or early environmental hazards, such as obstetric complications, play a role in projecting some individuals on a trajectory toward schizophrenia. High-risk and cohort studies demonstrate that children destined to develop schizophrenia tend to have delayed milestones and subtle neuromotor and cognitive impairments (particularly in coordination and language). These neurocognitive problems lead to difficulties in interpersonal relations, and their progressive alienation makes these at-risk children more likely to harbor odd or paranoid ideas. This cascade of increasingly deviant development may then be compounded by brain maturational changes during adolescence with a resultant lability of the dopaminergic response to stress. As a result, the individual is more susceptible to the effects of the abuse of dopamine-releasing drugs, and to other risk factors such as migration or stressful life events; social isolation may be a common pathway underlying several of the social risk factors.

Prefrontal deviations in function but not volume are putative endophenotypes for schizophrenia

This study sought to systematically investigate whether prefrontal cortex grey matter volume reductions are valid endophenotypes for schizophrenia, specifically investigating their presence in unaffected relatives, heritability, genetic overlap with the disorder itself and finally to contrast their performance on these criteria with putative neuropsychological indices of prefrontal functioning. We used a combined twin and family design and examined four prefrontal cortical regions of interest. Superior and inferior regions were significantly smaller in patients. However, the volumes of these same regions were normal in unaffected relatives and therefore, we could confirm that such deficits were not due to familial effects. Volumes of the prefrontal and orbital cortices were, however, moderately heritable, but neither shared a genetic overlap with schizophrenia. Total prefrontal cortical volume reductions shared a significant unique environmental overlap with the disorder, suggesting that the reductions were not familial. In contrast, prefrontal (executive) functioning deficits were present in the unaffected relatives, were moderately heritable and shared a substantial genetic overlap with liability to schizophrenia. These results suggest that the well recognized prefrontal volume reductions are not related to the same familial influences that increase schizophrenia liability and instead may be attributable to illness related biological changes or indeed confounded by illness trajectory, chronicity, medication or substance abuse, or in fact a combination of some or all of them.

Focal and global brain measurements in siblings of patients with schizophrenia

BACKGROUND

It remains unclear whether structural brain abnormalities in schizophrenia are caused by genetic and/or disease-related factors. Structural brain abnormalities have been found in nonpsychotic first-degree relatives of patients with schizophrenia, but results are inconclusive. This large magnetic resonance imaging study examined brain structures in patients with schizophrenia, their nonpsychotic siblings, and healthy control subjects using global and focal brain measurements.

METHODS

From 155 patients with schizophrenia, their 186 nonpsychotic siblings, and 122 healthy controls (including 25 sibling pairs), whole-brain scans were obtained. Segmentations of total brain, gray matter (GM), and white matter of the cerebrum, lateral and third ventricle, and cerebellum volumes were obtained. For each subject, measures of cortical thickness and GM density maps were estimated. Group differences in volumes, cortical thickness, and GM density were analyzed using Structural Equation Modeling, hence controlling for familial dependency of the data.

RESULTS

Patients with schizophrenia, but not their nonpsychotic siblings, showed volumetric differences, cortical thinning, and reduced GM density as compared with control subjects.

CONCLUSIONS

This study did not reveal structural brain abnormalities in nonpsychotic siblings of patients with schizophrenia compared with healthy control subjects using multiple imaging methods. Therefore, the structural brain abnormalities observed in patients with schizophrenia are for the largest part explained by disease-related factors.

The genetic and environmental determinants of the association between brain abnormalities and schizophrenia: the schizophrenia twins and relatives consortium

BACKGROUND

Structural brain abnormalities are consistently found in schizophrenia (Sz) and have been associated with the familial risk for the disorder. We aim to define the relative contributions of genetic and nongenetic factors to the association between structural brain abnormalities and Sz in a uniquely powered cohort (Schizophrenia Twins and Relatives consortium).

METHODS

An international multicenter magnetic resonance imaging collaboration was set up to pool magnetic resonance imaging scans from twin pairs in Utrecht (The Netherlands), Helsinki (Finland), London (United Kingdom), and Jena (Germany). A sample of 684 subjects took part, consisting of monozygotic twins (n = 410, with 51 patients from concordant and 52 from discordant pairs) and dizygotic twins (n = 274, with 39 patients from discordant pairs). The additive genetic, common, and unique environmental contributions to the association between brain volumes and risk for Sz were estimated by structural equation modeling.

RESULTS

The heritabilities of most brain volumes were significant and ranged between 52% (temporal cortical gray matter) and 76% (cerebrum). Heritability of cerebral gray matter did not reach significance (34%). Significant phenotypic correlations were found between Sz and reduced volumes of the cerebrum (-.22 [-.30/-.14]) and white matter (-.17 [-.25/-.09]) and increased volume of the third ventricle (.18 [.08/.28]). These were predominantly due to overlapping genetic effects (77%, 94%, and 83%, respectively).

CONCLUSIONS

Some of the genes that transmit the risk for Sz also influence cerebral (white matter) volume.

Association between hippocampal volume and P300 event related potential in psychosis: support for the Kraepelinian divide

INTRODUCTION

Abnormalities of the P300 event related potential (ERP) and of hippocampal structure are observed in individuals with psychotic disorders and their unaffected relatives. The understanding and clinical management of psychotic disorders are largely based on the descriptive Kraepelinian distinction between 'dementia praecox' and 'manic depressive psychosis', and not dependant on any well demarcated biological underpinnings. The hippocampus is postulated to be one of the main P300 generators, yet it remains unknown whether hippocampal volume decrements are associated with P300 deficits in psychosis, and whether any association is shared across non-affective and affective psychotic disorders.

METHODS

228 subjects from the Maudsley Family Psychosis Study comprising 55 patients with non-affective psychosis, 23 patients with psychotic bipolar disorder, 98 unaffected relatives, and 52 unrelated controls contributed structural MRI and ERP data. To study the relationship between hippocampal volume and P300 ERP, a seemingly unrelated regression methodology was used, accounting for whole brain volumes, clinical groups, age and gender in the analysis.

RESULTS

An association between left hippocampal volume and P300 latency in the combined sample comprising non-affective and affective psychotic patients, their relatives and controls was observed. There was an inverse relationship between brain structure and function in that prolongation of P300 latencies was associated with smaller left hippocampal volumes. On subdividing the sample based on Kraepelinian dichotomy, this association remained significant only for the non-affective psychosis group, comprising patients and their unaffected relatives.

CONCLUSIONS

Based on our findings, P300 latency, a measure of the speed of neural transmission, appears to be related to the size of the left hippocampus in schizophrenia, but not in psychotic bipolar disorder. It seems that underlying neuro-biological characteristics could help in unravelling the traditional Kraepelinian differentiation between the two major psychoses. The specificity of this brain structure-function association for schizophrenia opens the scope for further research using integration of multimodal biological data for objective categorisation of psychosis.

Putative structural neuroimaging endophenotypes in schizophrenia: a comprehensive review of the current evidence

The genetic contribution to schizophrenia etiopathogenesis is underscored by the fact that the best predictor of developing schizophrenia is having an affected first-degree relative, which increases lifetime risk by tenfold, as well as the observation that when both parents are affected, the risk of schizophrenia increases to approximately 50%, compared with 1% in the general population. The search to elucidate the complex genetic architecture of schizophrenia has employed various approaches, including twin and family studies to examine co-aggregation of brain abnormalities, studies on genetic linkage and studies using genome-wide association to identify genetic variations associated with schizophrenia. ‘Endophenotypes’, or ‘intermediate phenotypes’, are potentially narrower constructs of genetic risk. Hypothetically, they are intermediate in the pathway between genetic variation and clinical phenotypes and can supposedly be implemented to assist in the identification of genetic diathesis for schizophrenia and, possibly, in redefining clinical phenomenology.

MRI and X-ray scanning images of the brain of 3-, 6- and 9-month-old rats with bilateral neonatal ventral hippocampus lesions

Rats with bilateral neonatal ventral hippocampus lesions (NVHL) are commonly used for modeling developmental aspects of the pathophysiology of schizophrenia. Given that functional changes become significant only after puberty, NVHL as well as sham-operated rats were analyzed at the ages of 21, 42 and 63days (i.e. as pups, adolescents and adults), using MRI to examine the damage caused by surgery over time. Morphometric evaluations were considered and lesions were classified as small, medium and large. The volume of lesions increased regularly with age, to a greater extent than increases in overall brain size. This was relatively linear, corresponding to a gradually shrinking forebrain, and these observations held true for each class of lesions considered. Following the observation that the lesion procedure elicited calcifications in the brain, the same rats were subjected to 3D X-ray scanning the day after each MRI session, allowing precise measurements of skull size to be carried out. The NVHL rats had smaller skulls; however, the dimensions of the calcifications did not grow more than the skull size over time. The mechanisms underlying the progressive anatomical changes following surgery are discussed, and we propose this in vivo follow-up method to investigate therapeutic strategies aimed at countering or limiting the post-lesion consequences of a neonatal brain damage.

No effect of obstetric complications on basal ganglia volumes in schizophrenia

BACKGROUND

Heterogeneous findings have been reported in studies of basal ganglia volumes in schizophrenia patients as compared to healthy controls. The basal ganglia contain dopamine receptors that are known to be involved in schizophrenia pathology and to be vulnerable to pre- and perinatal hypoxic insults. Altered volumes of other brain structures (e.g. hippocampus and lateral ventricles) have been reported in schizophrenia patients with a history of obstetric complications (OCs). This is the first study to explore if there is a relationship between OCs and basal ganglia volume in schizophrenia.

METHODS

Thorough clinical investigation (including information on medication) of 54 schizophrenia patients and 54 healthy control subjects was undertaken. MR images were obtained on a 1.5T scanner, and volumes of nucleus caudatus, globus pallidum, putamen, and nucleus accumbens were quantified automatically. Information on OCs was blindly collected from original birth records.

RESULTS

Unadjusted estimates demonstrated a relationship between increasing number of OCs and larger volume of nucleus accumbens in schizophrenia patients and healthy controls. No statistically significant relationships were found between OCs and the basal ganglia volumes when controlled for intracranial volume, age, and multiple comparisons. There were no effects of typical versus atypical medication on the basal ganglia volumes. The patients with schizophrenia had larger globus pallidum volumes as compared to healthy controls, but there were no case-control differences for accumbens, putamen, or caudate volumes.

CONCLUSION

The present results do not support the hypothesis that OCs are related to alterations in basal ganglia volume in chronic schizophrenia.

Cerebral cortical thickness and a history of obstetric complications in schizophrenia

INTRODUCTION

Magnetic resonance imaging (MRI) studies have demonstrated that patients with schizophrenia have thinner brain cortices compared with healthy control subjects. Neurodevelopment is vulnerable to obstetric complications (OCs) such as hypoxia and birth trauma, factors that are also related to increased risk of developing schizophrenia. With the hypothesis that OCs might explain the thinner cortices found in schizophrenia, we studied patients with schizophrenia and healthy controls subjects for association between number and severity of OCs and variation in cortical thickness.

METHODS

MRI scans of 54 adults with schizophrenia or schizoaffective disorder and 54 healthy controls were acquired at Karolinska Institutet, Stockholm, Sweden. Measures of brain cortical thickness were obtained using automated computer processing (FreeSurfer). OCs were assessed from obstetric records and scored blindly according to the McNeil-Sjöström scale. At numerous cortical locations, putative effects of OCs on cortical thickness variation were tested for each trimester, for labour, for composite OC scores, severe OC scores, and hypoxia scores among patients and controls separately.

RESULTS

Number and severity of OCs varied among both patient and control subjects but were not associated with cortical thickness in either of the groups. Patients demonstrated thinner brain cortices but there were no significant differences in number and severity of OC scores across groups.

CONCLUSION

In the present study, number and severity of obstetric complications were not associated with brain cortical thickness, in patients with schizophrenia or in healthy control subjects. The thinner brain cortices found in patients with schizophrenia were not explained by a history of OCs.

Additive effect of NRG1 and DISC1 genes on lateral ventricle enlargement in first episode schizophrenia

Neuregulin 1 (NRG1) and Disrupted-in-schizophrenia (DISC1) genes, which are candidate genes for schizophrenia, are implicated in brain development. We have previously reported an association between the T allele of the rs6994992 SNP within NRG1 gene and lateral ventricle (LV) enlargement in first-episode schizophrenia patients. Moreover, transgenic mice with mutant DISC1 have also been reported as showing LV enlargement. In this study, we examined the possible interactive effects of NRG1 and DISC1 on brain volumes in a sample of first-episode schizophrenia patients. Ninety-one patients experiencing their first episode of schizophrenia underwent genotyping of three SNPs within DISC1 and structural brain MRI. These results were combined with our previously reported genotypes on three SNPs within NRG1. The T/T genotype of rs2793092 SNP in DISC1 was significantly associated with increased LV volume. However, taking into account the rs6994992 SNP in the NRG1 gene, which was also associated with LV volume in a previous study, the DISC1 SNP only predicted LV enlargement among those patients carrying the T allele in the NRG1 SNP. Those patients with the "at risk" allelic combinations in both genes had LV volumes which were 48% greater than those with none of the allelic combinations. Our findings suggest that NRG1 and DISC1 genes may be associated with brain abnormalities in schizophrenia through their influence on related pathways of brain development.

The effect of COMT, BDNF, 5-HTT, NRG1 and DTNBP1 genes on hippocampal and lateral ventricular volume in psychosis

BACKGROUND

Morphometric endophenotypes which have been proposed for psychotic disorders include lateral ventricular enlargement and hippocampal volume reductions. Genetic epidemiological studies support an overlap between schizophrenia and bipolar disorder, and COMT, BDNF, 5-HTT, NRG1 and DTNBP1 genes have been implicated in the aetiology of both these disorders. This study examined associations between these candidate genes and morphometric endophenotypes for psychosis.

METHOD

A total of 383 subjects (128 patients with psychosis, 194 of their unaffected relatives and 61 healthy controls) from the Maudsley Family Psychosis Study underwent structural magnetic resonance imaging and genotyping. The effect of candidate genes on brain morphometry was examined using linear regression models adjusting for clinical group, age, sex and correlations between members of the same family.

RESULTS

The results showed no evidence of association between variation in COMT genotype and lateral ventricular, and left or right hippocampal volumes. Neither was there any effect of the BDNF, 5-HTTLPR, NRG1 and DTNBP1 genotypes on these regional brain volumes.

CONCLUSIONS

Abnormal hippocampal and lateral ventricular volumes are among the most replicated endophenotypes for psychosis; however, the influences of COMT, BDNF, 5-HTT, NRG1 and DTNBP1 genes on these key brain regions must be very subtle if at all present.

Neuropsychological correlates of eye movement abnormalities in schizophrenic patients and their unaffected relatives

Impairments on neuropsychological and eye movement tasks have been demonstrated in schizophrenic patients and also reported in their unaffected relatives. However, it is not clear to what extent these phenotypes overlap. This study examined the relationship between specific eye movement and neuropsychological measures. The relationship between performance on eye movement and neuropsychological tasks was measured in 79 schizophrenic patients (63% from multiply affected families), 129 of their healthy first-degree relatives, and 72 normal controls. Antisaccade scores were correlated with most measures of neurocognitive functioning, and this correlation was strongest in schizophrenic patients in all cases. In the schizophrenic patients, but not their relatives or controls, the antisaccade distractibility error (ADE) score correlated significantly with current intelligence, verbal memory (immediate and delayed recall), and associative learning. In the case of crystallised IQ and delayed verbal memory, smaller correlations were present in unaffected relatives, although neither survived Bonferroni correction. Smooth pursuit performance was unrelated to any neuropsychological measure. Our study suggests that antisaccade errors are likely to represent part of a generalized neuropsychological deficit in schizophrenia.

A neuregulin 1 variant is associated with increased lateral ventricle volume in patients with first-episode schizophrenia

BACKGROUND

Structural brain abnormalities are already present at early phases of psychosis and might be the consequence of neurodevelopmental deviance. Neuregulin 1 gene (NRG1) is a candidate gene for schizophrenia, and its protein has different roles in nervous system development and plasticity. A single nucleotide polymorphism (SNP) within NRG1, SNP8NRG243177, has been associated with brain function among healthy and high-risk subjects and with reduced cell migration among patients with schizophrenia. We examined whether variations in this polymorphism influence brain volumes in first-episode schizophrenia subjects.

METHODS

Ninety-five minimally medicated patients experiencing their first episode of schizophrenia underwent genotyping of three SNPs within the NRG1 gene and structural brain magnetic resonance imaging (MRI). A comparison of volumes of lobar gray matter (GM), lateral ventricles, and cortical cerebrospinal fluid (CSF) was made between the groups according to their genotype after controlling for total intracranial volume.

RESULTS

The SNP8NRG243177 risk T allele was significantly associated, in an allele copy number-dependent fashion, with increased lateral ventricle volume. Genotype explained 7% of the variance of lateral ventricle volume. No significant differences in GM lobar or cortical CSF volumes were found among subgroups.

CONCLUSIONS

Our findings suggest that genetic variations of the NRG1 gene can contribute to the enlargement of the lateral ventricles described in early phases of schizophrenia. These results suggest novel lines of research into potential mechanisms by which schizophrenia susceptibility genes might exert their effect on brain structure.

Influence of obstetric complication severity on brain morphology in schizophrenia: an MR study

INTRODUCTION

The purpose of this study was to determine if a causal relationship exists between obstetric complications (OCs) severity and linear magnetic resonance (MR) measurements of brain atrophy in patients with schizophrenia.

MATERIALS AND METHODS

Linear measurements of ventricular enlargement (bifrontal span, Evans ratio, and bicaudate ratio) and hippocampal atrophy (interuncal distance) were completed on MR images obtained in 47 patients with schizophrenia. Regression analysis was used to look at association with OCs severity, assessed by the "Midwife protocol" of Parnas and colleagues. The relationship between MR measurements and phenomenologic variables such as age at onset, illness duration, and exposure to antipsychotic medications was explored. The relationship between MR measurements, OCs severity, and symptom presentation was also investigated.

RESULTS

OCs severity was significantly associated with MR measurements of ventricular enlargement (bifrontal span, Evans ratio). As the severity of OCs increased, bifrontal span and Evans ratio increased. This effect was independent of age at onset, illness duration, or even antipsychotic treatment. Interestingly, bifrontal span, Evans ratio, and OCs severity score all showed a significant positive correlation with hallucinatory symptomatology.

CONCLUSION

Although confirmatory studies are needed, our findings would support the idea that environmental factors, in this case severe OCs, might partly contribute to ventricular abnormalities in schizophrenia.

Functional magnetic resonance imaging (fMRI) of attention processes in presumed obligate carriers of schizophrenia: preliminary findings

BACKGROUND

Presumed obligate carriers (POCs) are the first-degree relatives of people with schizophrenia who, although do not exhibit the disorder, are in direct lineage of it. Thus, this subpopulation of first-degree relatives could provide very important information with regard to the investigation of endophenotypes for schizophrenia that could clarify the often contradictory findings in schizophrenia high-risk populations. To date, despite the extant literature on schizophrenia endophenotypes, we are only aware of one other study that examined the neural mechanisms that underlie cognitive abnormalities in this group. The aim of this study was to investigate whether a more homogeneous group of relatives, such as POCs, have neural abnormalities that may be related to schizophrenia.

METHODS

We used functional magnetic resonance imaging (fMRI) to collect blood oxygenated level dependent (BOLD) response data in six POCs and eight unrelated healthy controls while performing under conditions of sustained, selective and divided attention.

RESULTS

The POCs indicated alterations in a widely distributed network of regions involved in attention processes, such as the prefrontal and temporal (including the parahippocampal gyrus) cortices, in addition to the anterior cingulate gyrus. More specifically, a general reduction in BOLD response was found in these areas compared to the healthy participants during attention processes.

CONCLUSION

These preliminary findings of decreased activity in POCs indicate that this more homogeneous population of unaffected relatives share similar neural abnormalities with people with schizophrenia, suggesting that reduced BOLD activity in the attention network may be an intermediate marker for schizophrenia.

Schizophrenia: from developmental deviance to dopamine dysregulation

Two major theories of schizophrenia are respectively, the neurodevelopmental hypothesis and the dopamine hypothesis. Each of these has recently been revised. Firstly, the classical neurodevelopmental hypothesis has been modified to include the pathogenic effects of psychostimulants and cannabis abuse, and also of chronic social adversity; it is perhaps now more appropriately termed, the developmental hypothesis. Secondly, recent amendments to the dopamine hypothesis suggest that excess striatal dopamine is responsible for increased salience being given to insignificant events and thoughts, and that this underpins the development of psychotic symptoms. Traditionally, it has been thought that this striatal dopamine dysregulation might be secondary to frontal dysfunction. However, recent animal research shows that over-expression of striatal D(2) receptors results in frontal dysfunction manifesting as cognitive difficulties and animal equivalents of so-called negative symptoms. This raises the question whether early intervention may prevent the development of these latter problems. Finally, the two theories are beginning to be integrated through the growing evidence that all the developmental risk factors which increase risk of schizophrenia appear to act by facilitating dopamine dysregulation.

Auditory P300 in patients with bipolar disorder and their unaffected relatives

OBJECTIVES

There is evidence that genetic susceptibility may be shared between bipolar disorder (BD) and schizophrenia, but electrophysiological phenotypes which have been extensively used in studies of genetic susceptibility for schizophrenia remain far less explored in bipolar illness. This study assesses whether auditory P300 latency delays and amplitude reductions, which have been demonstrated in patients with schizophrenia and their unaffected first-degree relatives, are associated with familial liability to psychotic bipolar illness.

METHODS

The P300 auditory evoked potential was obtained using an oddball task from 37 participants with BD who had a history of psychotic symptoms, 38 of their unaffected first-degree relatives and 42 healthy unrelated comparison subjects. Patients and relatives came from families multiply affected with BD or another functional psychotic disorder. P300 amplitude and latency at midline sites were compared between the groups, using linear regression analyses and robust variance estimators for clustered data, including age and gender as covariates.

RESULTS

Bipolar disorder patients with a history of psychosis and their unaffected relatives showed significantly delayed P300 latency at Pz compared to controls. The groups did not differ in P300 amplitude.

CONCLUSIONS

P300 latency delays are associated with both psychotic BD and familial liability for this illness. Sample size limited our ability to test for multimodal distribution of P300 measures among relatives, which might be expected if only a subgroup inherits any deficits. In future it will be of interest to directly compare groups of families with psychotic and non-psychotic forms of BD to explore further the role of psychotic symptoms with regard to P300 measures in the disorder. Our results indicate that delayed P300 latency is a promising candidate endophenotype for psychotic BD, as well as schizophrenia, and may reflect the impact of shared susceptibility genes for both types of psychosis.

Executive function and genetic predisposition to schizophrenia--the Maudsley family study

Executive cognitive impairment has been found in families affected by schizophrenia and is a putative endophenotype. We wished to explore its genetic basis further by studying the association between impairment and genetic loading for schizophrenia. We studied 30 schizophrenia patients with a family history of schizophrenia, 53 of their nonpsychotic first-degree relatives (familial), 32 patients with schizophrenia but no known family history of psychosis, 52 of their first-degree relatives (nonfamilial), and 47 normal controls. They were tested using the National Adult Reading Test (NART), Trails A and B, Verbal fluency tasks, and a computerized version of the Wisconsin Card Sorting Test (WCST). Familial, but not nonfamilial, relatives were impaired on NART, letter fluency, Trails B, and WCST total errors. They were inferior to nonfamilial relatives on letter fluency and Trails A. Both sets of relatives were impaired on Trails B controlling for Trails A, and on WCST categories achieved. There were no significant differences between schizophrenia patients with and without a family history. Our results suggest that executive deficits qualitatively similar to those seen in those with schizophrenia reflect familial susceptibility, even taking early IQ and education into consideration, consistent with a genetic mechanism.

MRI brain volume abnormalities in young, nonpsychotic relatives of schizophrenia probands are associated with subsequent prodromal symptoms

Schizophrenia is characterized by subtle but well-replicated total and regional (frontal and temporal) brain tissue volume deficits. Studies of individuals at-risk for developing schizophrenia suggest that the onset of brain volume decrement may closely pre-date overt manifestations of schizophrenia, making brain volume abnormalities potential predictors for early identification. In an ongoing longitudinal morphometric MRI study of young, nonpsychotic first- or second-degree relatives of schizophrenia probands, we compared brain volumes in 46 relatives who are still within age range for developing schizophrenia against comparison groups of 46 schizophrenia patients and 46 healthy volunteers without family history of schizophrenia. Relatives had similar brain volume abnormalities as schizophrenia patients albeit less severe. Relatives had significantly larger whole brain, frontal, temporal and parietal gray matter (GM) volumes than patients. Relatives also had significantly smaller frontal GM volumes than healthy volunteers. Both relatives and patients had significantly larger whole brain WM (specifically parietal WM) volumes compared to healthy volunteers. Abnormally greater WM volumes in relatives and patients are suggestive of genetically-mediated dysmaturation of the age-expected myelination during adolescence through mid adulthood. On prodromal symptoms assessed in relatives one year after MRI brain scans, initial GM deficits as well as larger WM volumes correlated significantly with greater severity of subsequent prodromal symptoms. Together with previous genetic high-risk studies of adolescent or young adult relatives, these findings indicate that premorbid MRI brain abnormalities may be of predictive value for the early identification of schizophrenia.

The neurobiological underpinnings of risk and conversion in relatives of patients with schizophrenia

Schizophrenia is associated with deficits in many domains of cognitive function, along with structural and functional brain abnormalities, most notably in prefrontal and temporal lobes. In recent years, a number of research groups have turned to the study of relatives of affected individuals with the aim of determining if similar cognitive deficits and brain abnormalities are also found in those with increased genetic vulnerability to the disorder. In this article studies on such individuals are discussed. It is concluded that deficits are generally apparent in relatives, which are similar to but less marked than those seen in patients with schizophrenia. The literature on predictors of conversion in people at genetic high risk is much smaller, but suggests a combination of baseline trait severity and further change in key measures.

Three-dimensional MRI perfusion maps: a step beyond volumetric analysis in mental disorders

A new type of magnetic resonance imaging analysis, based on fusion of three-dimensional reconstructions of time-to-peak parametric maps and high-resolution T1-weighted images, is proposed in order to evaluate the perfusion of selected volumes of interest. Because in recent years a wealth of data have suggested the crucial involvement of vascular alterations in mental diseases, we tested our new method on a restricted sample of schizophrenic patients and matched healthy controls. The perfusion of the whole brain was compared with that of the caudate nucleus by means of intrasubject analysis. As expected, owing to the encephalic vascular pattern, a significantly lower time-to-peak was observed in the caudate nucleus than in the whole brain in all healthy controls, indicating that the suggested method has enough sensitivity to detect subtle perfusion changes even in small volumes of interest. Interestingly, a less uniform pattern was observed in the schizophrenic patients. The latter finding needs to be replicated in an adequate number of subjects. In summary, the three-dimensional analysis method we propose has been shown to be a feasible tool for revealing subtle vascular changes both in normal subjects and in pathological conditions.

Which perspectives can endophenotypes and biological markers offer in the early recognition of schizophrenia?

The early recognition of schizophrenia seems crucial; various studies relate a longer duration-of-untreated-psychosis to a worse prognosis. We give an overview over common psychopathological early recognition instruments (BSABS, CAARMS, SIPS, IRAOS, ERIraos). However, many clinical symptoms of prodromal schizophrenia stages are not sufficiently specific. Thus we review recent contributions of neuroimaging and electrophysiological as well as genetic studies: which new diagnostic perspectives offer endophenotypes (such as P300, P50 sensory gating, MMN, smooth pursuit eye movements; indicating a specific genetic vulnerability) together with a better understanding of schizophrenic pathophysiology (state-dependent biological markers, e.g. aggravated motor neurological soft signs during psychosis) in prodromal schizophrenia when still ambiguous clinical symptoms are present. Several examples (e.g. from COMT polymorphisms to working memory deficits) illustrate more specific underlying neuronal mechanisms behind behavioural symptoms. This way, a characteristic pattern of disturbed cerebral maturation might be distinguished in order to complement clinical instruments of early schizophrenia detection.

TRP's: links to schizophrenia?

Schizophrenia is a chronic psychiatric disorder the cause of which is unknown. It is considered to be a neurodevelopmental disorder that results from an interaction of genetic and environmental factors. Direct evidence for links between schizophrenia and TRP channels is lacking. However, several aspects of the pathophysiology of the disorder point to a possible involvement of TRP channels. In this review evidence for links between TRP channels and schizophrenia with respect to neurodevelopment, dopaminergic and cannabinoid systems, thermoregulation, and sensory processes, is discussed. Investigation of these links holds the prospect of a new understanding of schizophrenia with resultant therapeutic advances.

Relationship of catechol-O-methyltransferase variants to brain structure and function in a population at high risk of psychosis

BACKGROUND

There is growing evidence that the gene catechol-O-methyltransferase (COMT) is involved in the etiopathogenesis of schizophrenia. This study sought to clarify the effects of the COMT Val158Met polymorphism on brain structure, function, and risk of developing schizophrenia in a well-characterized cohort of individuals at high risk of schizophrenia for familial reasons.

METHODS

In a sample of 78 people at high genetic risk of schizophrenia, the risk of progression to schizophrenia associated with the COMT Val allele was estimated. The relationship of the Val allele to brain structure and function was investigated using structural magnetic resonance imaging (sMRI) and functional magnetic resonance imaging (fMRI) data collected on the high-risk subjects before their disease outcome was known.

RESULTS

The COMT Val allele increased the risk of schizophrenia in this cohort in a dose-dependent manner. Subjects with the COMT Val allele had reduced gray matter density in anterior cingulate cortex. In addition, there was evidence of increased activation in lateral prefrontal cortex and anterior and posterior cingulated, with increasing sentence difficulty in those with the COMT Val allele despite a similar level of performance.

CONCLUSIONS

The COMT Val allele is associated with an increased risk of schizophrenia in subjects at increased familial risk, in whom it has demonstrable effects on prefrontal brain structure and function. These patterns of altered brain structure and function have previously been associated with schizophrenia in this and other samples.

Adjudicating neurocognitive endophenotypes for schizophrenia

Although genetic influences on schizophrenia are well established, localization of the genes responsible for this illness has proven extremely difficult. Given evidence that genes predisposing to schizophrenia may be transmitted without expression of the clinical phenotype, efforts have focused on developing endophenotypes. While several neuropsychological measures have been proposed to be endophenotypes, few studies have systematically assessed batteries of neurocognitive tests to determine which tests are most sensitive to liability for the illness. Two hundred sixty-nine Latino individuals were administered a standard neuropsychological battery. Two hundred fourteen of these were members of families with at least two siblings diagnosed with schizophrenia or schizoaffective disorder. The remaining were community controls without history of major psychiatric illness. Neurocognitive measures found to be heritable were entered into analyses designed to determine which tests covary with the degree of genetic relationship to affected individuals. Although five measures were found to uniquely model genetic liability for schizophrenia, digit symbol coding was the most sensitive. To assess the specificity of these endophenotypes, performance on these measures were compared to family members with bipolar and unipolar affective disorders. These markers clearly distinguished between individuals with psychotic illnesses and those with major depression. As measures contributed uniquely to discriminate individuals at varying risk for schizophrenia, our findings imply multiple independently inherited elements to the liability for the illness. We present a practical model for adjudicating endophenotypes and determining which measures are best suited for use in linkage analyses.

The endophenotype concept in psychiatric genetics

The idea that some phenotypes bear a closer relationship to the biological processes that give rise to psychiatric illness than diagnostic categories has attracted considerable interest. Much effort has been devoted to finding such endophenotypes, partly because it is believed that the genetic basis of endophenotypes will be easier to analyse than that of psychiatric disease. This belief depends in part on the assumption that the effect sizes of genetic loci contributing to endophenotypes are larger than those contributing to disease susceptibility, hence increasing the chance that genetic linkage and association tests will detect them. We examine this assumption by applying meta-analytical techniques to genetic association studies of endophenotypes. We find that the genetic effect sizes of the loci examined to date are no larger than those reported for other phenotypes. A review of the genetic architecture of traits in model organisms also provides no support for the view that the effect sizes of loci contributing to phenotypes closer to the biological basis of disease is any larger than those contributing to disease itself. While endophenotype measures may afford greater reliability, it should not be assumed that they will also demonstrate simpler genetic architecture.

Sensory gating deficits, pattern completion, and disturbed fronto-limbic balance, a model for description of hallucinations and delusions in schizophrenia

Schizophrenia, if not the most difficult, is one of the most difficult mysterious puzzles for psychiatrists, psychologists, and neuroscientists to solve. In this paper, based on the previously known pathologies of schizophrenia, a new model is proposed for explanation of the formation of positive psychotic symptoms of hallucinations and delusions. This model can be used for understanding psychotic or psychotic-like positive symptoms of bipolar mood disorder, posttraumatic stress disorder, obsessive compulsive, and amphetamine and drug-induced psychotic disorders. Based on the postulated model, a spectral view on these disorders with psychotic features is also proposed. These pathologies include auditory sensory gating deficits in hippocampus, abnormal emotional coding in amygdala, pattern completion in thalamic and cortical areas, and disturbed fronto-limbic balance. This model includes anatomical and neurotransmitter defects of hippocampus, amygdala, thalamus, cingula, and prefrontal cortex and their interconnections. A role for hippocampal sensory gating deficits in the pathogenesis of positive psychotic symptoms and interrelation between amygdala and its dopamine level with hippocampus is speculated. This model also hires the interesting function of pattern completion in thalamus and cortical areas for a better explanation of the pathogenesis of hallucinations and delusional psychotic symptoms. Furthermore, there is also explanation for the polygenic etiology of the schizophrenic and psychotic disorders and relation between schizophrenia and bipolar mood disorder in anatomy and neural systems involved. A spectral view is proposed that explains the absence of clear cut border between different psychotic or psychotic-like disorders in their form and severity based on the involved genes and brain functional systems. Including excessive prefrontal pruning, there is also explanation for the appearance of positive psychotic symptoms in early adulthood. An explanation for the high dopamine level of amygdala despite its decreased size and abnormal anatomy is also suggested as a compensatory function which might explain the decline in positive psychotic symptoms when schizophrenics age according to amygdala burn out. Based on this model, speculations are provided for: late onset of the effects of antipsychotics on positive psychotic symptoms, mechanism for the therapeutic effect of serotonin type 2A receptor blockers and GABAergic medications in psychosis, role of smoking in diminution of psychotic symptoms, and relationship between biological and psychological issues in the formation of psychotic symptoms. Finally, based on this model, a new role for nicotinic cholinergic drugs (such as galantamine) for treatment of schizophrenia and other psychotic or psychotic-like disorders is proposed.

Cerebral asymmetry in 14 year olds born very preterm

The normal pattern of cerebral asymmetry may be altered in neurodevelopmental disorders such as autism and schizophrenia. Babies born very preterm have an increased risk of brain damage, and brain abnormalities which persist into adolescence. This study aimed to ascertain whether preterm birth affects the development of fronto-occipital asymmetry. Structural MRI (magnetic resonance imaging) scans from 14 year old individuals born very preterm (n = 61; mean age 14 years 11 months; 29 male) and age-matched full-term controls (n = 49; mean age 14 years 11 months; 31 male) underwent morphometric analysis, using well-validated stereological methods. Measurements of right and left prefrontal, premotor, sensorimotor and occipitoparietal regional volumes were made and asymmetry indices calculated. These factors underwent a reductive factor analysis. There were no significant between-group differences in fronto-occipital asymmetry between the preterm adolescents and their full-term counterparts. It seems unlikely, therefore, that preterm birth per se deviates the development of normal fronto-occipital asymmetry. Neonatal periventricular haemorrhage with ventricular dilatation revealed by ultrasound may be associated with reversal of asymmetry in the sensorimotor area.

Intrinsic sensory deprivation induced by neonatal capsaicin treatment induces changes in rat brain and behaviour of possible relevance to schizophrenia

Schizophrenia is considered to be a neurodevelopmental disorder with origins in the prenatal or neonatal period. Brains from subjects with schizophrenia have enlarged ventricles, reduced cortical thickness (CT) and increased neuronal density in the prefrontal cortex compared with those from normal subjects. Subjects with schizophrenia have reduced pain sensitivity and niacin skin flare responses, suggesting that capsaicin-sensitive primary afferent neurons might be abnormal in schizophrenia. This study tested the hypothesis that intrinsic somatosensory deprivation, induced by neonatal capsaicin treatment, causes changes in the brains of rats similar to those found in schizophrenia. Wistar rats were treated with capsaicin, 50 mg kg(-1) subcutaneously, or vehicle (control) at 24-36 h of life. At 5-7 weeks behavioural observations were made, and brains removed, fixed and sectioned. The mean body weight of capsaicin-treated rats was not significantly different from control, but the mean brain weight of male, but not female, rats, was significantly lower than control. Capsaicin-treated rats were hyperactive compared with controls. The hyperactivity was abolished by haloperidol. Coronal brain sections of capsaicin-treated rats had smaller cross-sectional areas, reduced CT, larger ventricles and aqueduct, smaller hippocampal area and reduced corpus callosum thickness, than brain sections from control rats. Neuronal density was increased in several cortical areas and the caudate putamen, but not in the visual cortex. It is concluded that neonatal capsaicin treatment of rats produces brain changes that are similar to those found in brains of subjects with schizophrenia.

Magnetic resonance imaging study of the ventricle-brain ratio in parents of schizophrenia subjects

Structural abnormalities found in probands with schizophrenia have been reported to occur to some degree in their unaffected relatives. However, there has yet to be a study that has focused on brain changes of parents of schizophrenics who are not the presumed obligate carriers. Using MRI, the authors studied the ventricle-brain ratio (VBR) of 9 pairs of parents of schizophrenics and 18 age- and sex-matched healthy controls. VBRs of the unaffected parents of schizophrenics were significantly larger than those of the controls. Our results suggest that large VBRs aggregate in the parents of schizophrenics and may serve as an indicator of vulnerability to the disorder.

Reduced cerebellar volume and neurological soft signs in first-episode schizophrenia

Recent studies indicate that morphological and functional abnormalities of the cerebellum are associated with schizophrenia. Since the cerebellum is crucial for motor coordination, one may ask whether the respective changes are associated with motor dysfunction in the disease. To test these hypotheses in a clinical study, we investigated cerebellar volumes derived from volumetric magnetic resonance imaging of 37 first-episode patients with schizophrenia, schizophreniform or schizoaffective disorder and 18 healthy controls matched for age, gender and handedness. To control for potential interindividual differences in head size, intracranial volume was entered as a covariate. Neurological soft signs (NSS) were examined after remission of acute symptoms. Compared with the controls, patients had significantly smaller cerebellar volumes for both hemispheres. Furthermore, NSS in patients were inversely correlated with tissue volume of the right cerebellar hemisphere partialling for intracranial volume. No associations were detected between cerebellar volumes and psychopathological measures obtained at hospital admission when patients were in the acute psychotic state or after remission, treatment duration until remission, treatment response or prognostic factors, respectively. These findings support the hypothesis of cerebellar involvement in schizophrenia and indicate that the respective changes are associated with NSS.

Eye tracking in schizophrenia: does the antisaccade task measure anything that the smooth pursuit task does not?

Smooth pursuit and antisaccade eye-tracking abnormalities have been proposed as endophenotypes for schizophrenia. However, it is not clear whether these tasks measure the same underlying abnormality. We hypothesised that these measures would be correlated. The association between smooth pursuit and antisaccade task performance was assessed in 50 schizophrenic patients, 80 unaffected first-degree relatives and 40 unaffected controls. Smooth pursuit measures included gain, number of saccades and a qualitative measure of smooth pursuit. The antisaccade distractibility error (ADE) score was the only measure of the antisaccade task. A significant correlation was found between reduced gain and an increased ADE score for all the subjects in the three groups combined. The total number of saccades was negatively correlated with the ADE score in the schizophrenic group, but positively in the relative group. Qualitative ratings of smooth pursuit correlated with the ADE score. Our results suggest that the antisaccade distractibility error score is related to gain and qualitative measures of smooth pursuit, although the relationship with number of saccades did not conform to this pattern. The finding may reflect a shared genetic liability, that affects both eye-tracking phenotypes. It is likely that both measures reflect frontal cortical dysfunction.