Lower prepulse inhibition in children with the 22q11 deletion syndrome

Reduced amplitude and slowed latency of the acoustic startle response in adolescents and adults with 22q11.2 deletion syndrome

BACKGROUND

22q11.2 deletion syndrome (22q11DS) is one of the most robust genetic predictors of psychosis and other psychiatric illnesses. In this study, we examined 22q11DS subjects' acoustic startle responses (ASRs), which putatively index psychosis risk. Latency of the ASR is a presumptive marker of neural processing speed and is prolonged (slower) in schizophrenia. ASR measures correlate with increased psychosis risk, depend on glutamate and dopamine receptor signaling, and could serve as translational biomarkers in interventions for groups at high psychosis risk.

METHODS

Startle magnitude, latency, and prepulse inhibition were assessed with a standard acoustic startle paradigm in 31 individuals with 22q11.2DS and 32 healthy comparison (HC) subjects. Surface electrodes placed on participants' orbicularis oculi recorded the electromyographic signal in ASR eyeblinks. Individuals without measurable startle blinks in the initial habituation block were classified as non-startlers.

RESULTS

Across the startle session, the ASR magnitude was significantly lower in 22q11DS subjects than HCs because a significantly higher proportion of 22q11DS subjects were non-startlers. Latency of the ASR to pulse-alone stimuli was significantly slower in 22q11DS than HC subjects. Due to the overall lower 22q11DS startle response frequency and magnitudes prepulse inhibition could not be analyzed.

CONCLUSIONS

Reduced magnitude and slow latency of 22q11DS subjects' responses suggest reduced central nervous system and neuronal responsiveness. These findings are consistent with significant cognitive impairments observed in 22q11DS subjects. Further research is needed to untangle the connections among basic neurotransmission dysfunction, psychophysiological responsiveness, and cognitive impairment.

Evidence for Prepulse Inhibition of Visually Evoked Motor Response in Drosophila melanogaster

Prepulse inhibition (PPI) is a widely investigated behavior to study the mechanisms of disorders such as anxiety, schizophrenia, and bipolar mania. PPI has been observed across various vertebrate and invertebrate species; however, it has not yet been reported in adult Drosophila melanogaster. In this study, we describe the first detection of PPI of visually evoked locomotor arousal in flies. To validate our findings, we demonstrate that PPI in Drosophila can be partially reverted by the N-methyl D-aspartate (NMDA) receptor antagonist MK-801, known for inducing sensorimotor gating deficits in rodent models. Additionally, we show that the visually evoked response can be inhibited by multiple stimuli presentation, which can also be affected by MK-801. Given the versatility of Drosophila as a model organism for genetic screening and analysis, our results suggest that high-throughput behavioral screenings of adult flies can become a valuable tool for investigating the mechanisms behind PPI.

Df(h22q11)/+ mouse model exhibits reduced binding levels of GABAA receptors and structural and functional dysregulation in the inhibitory and excitatory networks of hippocampus

The 22q11.2 hemizygous deletion confers high risk for multiple neurodevelopmental disorders. Inhibitory signaling, largely regulated through GABA_A receptors, is suggested to serve a multitude of brain functions that are disrupted in the 22q11.2 deletion syndrome. We investigated the putative deficit of GABA_A receptors and the potential substrates contributing to the inhibitory and excitatory dysregulations in hippocampal networks of the Df(h22q11)/+ mouse model of the 22q11.2 hemizygous deletion. The Df(h22q11)/+ mice exhibited impairments in several hippocampus-related functional domains, represented by impaired spatial memory and sensory gating functions. Autoradiography using the [³H]muscimol tracer revealed a significant reduction in GABA_A receptor binding in the CA1 and CA3 subregions, together with a loss of GAD67⁺ interneurons in CA1 of Df(h22q11)/+ mice. Furthermore, electrophysiology recordings exhibited significantly higher neuronal activity in CA3, in response to the GABA_A receptor antagonist, bicuculline, as compared with wild type mice. Density and volume of dendritic spines in pyramidal neurons were reduced and Sholl analysis also showed a reduction in the complexity of basal dendritic tree in CA1 and CA3 subregions of Df(h22q11)/+ mice. Overall, our findings demonstrate that hemizygous deletion in the 22q11.2 locus leads to dysregulations in the inhibitory circuits, involving reduced binding levels of GABA_A receptors, in addition to functional and structural modulations of the excitatory networks of hippocampus.

Altered functional brain dynamics in chromosome 22q11.2 deletion syndrome during facial affect processing

Chromosome 22q11.2 deletion syndrome (22q11.2DS) is a multisystem disorder associated with multiple congenital anomalies, variable medical features, and neurodevelopmental differences resulting in diverse psychiatric phenotypes, including marked deficits in facial memory and social cognition. Neuroimaging in individuals with 22q11.2DS has revealed differences relative to matched controls in BOLD fMRI activation during facial affect processing tasks. However, time-varying interactions between brain areas during facial affect processing have not yet been studied with BOLD fMRI in 22q11.2DS. We applied constrained principal component analysis to identify temporally overlapping brain activation patterns from BOLD fMRI data acquired during an emotion identification task from 58 individuals with 22q11.2DS and 58 age-, race-, and sex-matched healthy controls. Delayed frontal-motor feedback signals were diminished in individuals with 22q11.2DS, as were delayed emotional memory signals engaging amygdala, hippocampus, and entorhinal cortex. Early task-related engagement of motor and visual cortices and salience-related insular activation were relatively preserved in 22q11.2DS. Insular activation was associated with task performance within the 22q11.2DS sample. Differences in cortical surface area, but not cortical thickness, showed spatial alignment with an activation pattern associated with face processing. These findings suggest that relative to matched controls, primary visual processing and insular function are relatively intact in individuals with 22q11.22DS, while motor feedback, face processing, and emotional memory processes are more affected. Such insights may help inform potential interventional targets and enhance the specificity of neuroimaging indices of cognitive dysfunction in 22q11.2DS.

A Methyltransferase Inhibitor (Decitabine) Alleviates Intergenerational Effects of Paternal Neonatal Exposure to Anesthesia With Sevoflurane

BACKGROUND

Neonatal exposure to sevoflurane induces neurobehavioral and neuroendocrine abnormalities in exposed male rats (generation F0) and neurobehavioral, but not neuroendocrine, abnormalities in their male, but not female, offspring (generation F1). These effects of sevoflurane are accompanied by a hypermethylated neuron-specific K-2Cl (Kcc2) Cl exporter gene in the F0 spermatozoa and the F1 male hypothalamus, while the gene's expression is reduced in the F0 and F1 hypothalamus. We investigated whether inhibition of deoxyribonucleic acid methyltransferases (DNMTs) before paternal sevoflurane exposure could alleviate the anesthetic's F0 and F1 effects.

METHODS

Sprague-Dawley male rats were anesthetized with 2.1% sevoflurane for 5 hours on postnatal day (P) 5 and mated with control females on P90 to generate offspring. The nonselective DNMT inhibitor decitabine (0.5 mg/kg, intraperitoneally) was administered 30 minutes before sevoflurane exposure. The F0 and F1 male rats were evaluated in in vivo and in vitro tests in adulthood.

RESULTS

Paternal exposure to sevoflurane induced impaired prepulse inhibition of the acoustic startle response and exacerbated corticosterone responses to stress in F0 males and impaired prepulse inhibition of the startle responses in F1 males. These effects were accompanied in both generations by reduced and increased expressions of hypothalamic Kcc2 and Dnmt3a/b, respectively. Decitabine deterred the effects of paternal exposure to sevoflurane in F0 and F1 males.

CONCLUSIONS

These results suggest that similar decitabine-sensitive mechanisms regulating expression of multiple genes are involved in the mediation of neurobehavioral abnormalities in sires neonatally exposed to sevoflurane and in their future unexposed male offspring.

Neural and behavioral measures suggest that cognitive and affective functioning interactions mediate risk for psychosis-proneness symptoms in youth with chromosome 22q11.2 deletion syndrome

Behavioral components of chromosome 22q11.2 deletion syndrome (22q), caused by the most common human microdeletion, include cognitive and adaptive functioning impairments, heightened anxiety, and an elevated risk of schizophrenia. We investigated how interactions between executive function and the largely overlooked factor of emotion regulation might relate to the incidence of symptoms of psychotic thinking in youth with 22q. We measured neural activity with event-related potentials (ERPs) in variants of an inhibitory function (Go/No-Go) experimental paradigm that presented affective or non-affective stimuli. The study replicated inhibition impairments in the 22q group that were amplified in the presence of stimuli with negative, more than positive affective salience. Importantly, the anterior N2 conflict monitoring ERP significantly increased when youth with 22q viewed angry and happy facial expressions, unlike the typically developing participants. This suggests that youth with 22q may require greater conflict monitoring resources when controlling their behavior in response to highly salient social signals. This evidence of both behavioral and neurophysiological differences in affectively influenced inhibitory function suggests that frequently anxious youth with 22q may struggle more with cognitive control in emotionally charged social settings, which could influence their risk of developing symptoms of psychosis.

Estimating the causal effect of prenatal lead exposure on prepulse inhibition deficits in children and adolescents

During pregnancy, maternal lead from earlier exposures mobilizes and crosses placental barriers, placing the developing fetus at risk for lead exposure and neurodevelopmental deficits. Some neuronal circuits known to be affected in neurodevelopment disorders can be probed with simple physiological behavioral paradigms. One such neural biomarker is Pre-Pulse Inhibition (PPI), an indicator of adequate sensorimotor gating processing. In clinical studies, deficits in PPI have been associated with neurodevelopmental disorders in human subjects. To our knowledge, no studies have examined the use of PPI as a biomarker of toxicant effects on the brain in epidemiological studies. We aimed to estimate the causal effect of prenatal lead exposure, assessed by maternal cortical bone lead concentrations, on PPI in 279 children from Mexico City. in vivo maternal cortical bone lead measurements were taken at four weeks postpartum at the mid-tibia shaft using a K-Shell X-ray fluorescence instrument. PPI recording occurred in an isolated clinical setting and eye blink responses were measured using electromyography. We assessed if the conditions for causal inference held in our study and used the results of our assessment to estimate the causal effect of prenatal lead exposure on PPI using an ordinary least squares regression model, a marginal structural model, and the parametric g-formula. Results were consistent across the three modeling approaches. For the parametric g-formula, a one standard deviation (10.0 μg/g) increase in prenatal lead significantly reduced PPI by approximately 19.0 % (95 % CI: 5.4 %, 34.3 %). This decrease is similar in magnitude to clinical studies on schizophrenia, which have observed PPI impairments in patients with schizophrenia as compared to controls. Our results are consistent with findings from other studies establishing an association between lead exposure and neurodevelopmental disorders in children and suggest that PPI may be useful as an objective biomarker of toxicant effects on the brain.

Socio-demographic predictors of prepulse inhibition: A prospective study in children and adolescents from Mexico City

Prepulse inhibition (PPI) is a sensorimotor gating mechanism that reduces interfering influences to the neural processing of incoming stimuli, and is associated with several neurodevelopmental disorders. To date, research on PPI and neurodevelopmental disorders has primarily been in cross-sectional, clinical settings. In this prospective, epidemiologic study, we used a data-driven prediction model to identify socio-demographic predictors of PPI in children and adolescents from Mexico City to inform future etiologic studies evaluating PPI. We conducted variable selection and validation using a modified version of the multiple imputation random lasso (MIRL) variable selection algorithm. MIRL identified six predictors of PPI at a stimulus onset asynchrony of 120 ms or 240 ms. Of those six predictors, maternal education, birthweight, and total breastfeeding months were highlighted as previously unstudied variables associated with enhanced PPI. Our findings highlight the potential value of PPI as an adjunct screening tool for identifying children at risk for neurodevelopmental disorders and underscore the relevance for validation research on this topic.

Can Animal Models of Copy Number Variants That Predispose to Schizophrenia Elucidate Underlying Biology?

The diagnosis of schizophrenia rests on clinical criteria that cannot be assessed in animal models. Together with absence of a clear underlying pathology and understanding of what causes schizophrenia, this has hindered development of informative animal models. However, recent large-scale genomic studies have identified copy number variants (CNVs) that confer high risk of schizophrenia and have opened a new avenue for generation of relevant animal models. Eight recurrent CNVs have reproducibly been shown to increase the risk of schizophrenia by severalfold: 22q11.2(del), 15q13.3(del), 1q21(del), 1q21(dup), NRXN1(del), 3q29(del), 7q11.23(dup), and 16p11.2(dup). Five of these CNVs have been modeled in animals, mainly mice, but also rats, flies, and zebrafish, and have been shown to recapitulate behavioral and electrophysiological aspects of schizophrenia. Here, we provide an overview of the schizophrenia-related phenotypes found in animal models of schizophrenia high-risk CNVs. We also discuss strengths and limitations of the CNV models, and how they can advance our biological understanding of mechanisms that can lead to schizophrenia and can be used to develop new and better treatments for schizophrenia.

Dependency of prepulse inhibition deficits on baseline startle reactivity in a mouse model of the human 22q11.2 microdeletion syndrome

Hemizygous microdeletion at the chromosomal locus 22q11.2 is a copy number variation with strong genetic linkage to schizophrenia and related disorders. This association, along with its phenotypic overlap with the 22q11.2 microdeletion syndrome, has motivated the establishment of Df[h22q11]/+ mice, in which the human 22q11.2 orthologous region is deleted. Previous investigations using this model showed the presence of reduced prepulse inhibition (PPI) of the acoustic startle reflex, a form of sensorimotor gating known to be impaired in a number of psychiatric disorders. Concomitantly to reduced PPI, however, Df[h22q11]/+ mice are also characterized by a robust increase in baseline startle reactivity, which may complicate or confound the interpretation of PPI. Therefore, the present study re-examined the relationship between acoustic startle reactivity and PPI in this mouse model. We found that while PPI is reduced in Df[h22q11]/+ mice when using its relative indexation (ie, % PPI), this deficit is no longer apparent when using the absolute quantification, that is, the direct comparison between pulse-alone and prepulse-plus-pulse conditions with successively increasing prepulse intensities. We further identified marked negative correlations between % PPI and startle reactivity in Df[h22q11]/+ mice. Moreover, when stratifying Df[h22q11]/+ mice into subgroups displaying low- and high-startle reactivity, only the latter subgroup displayed a significant reduction in % PPI. Collectively, our data suggest that alterations in baseline startle reactivity can confound the outcomes and interpretation of PPI in this mouse model of the human 22q11.2 microdeletion syndrome.

Meta-analysis on the association between genetic polymorphisms and prepulse inhibition of the acoustic startle response

Sensorimotor gating measured by prepulse inhibition (PPI) of the acoustic startle response (ASR) has been proposed as one of the most promising electrophysiological endophenotypes of schizophrenia. During the past decade, a number of publications have reported significant associations between genetic polymorphisms and PPI in samples of schizophrenia patients and healthy volunteers. However, an overall evaluation of the robustness of these results has not been published so far. Therefore, we performed the first meta-analysis of published and unpublished associations between gene polymorphisms and PPI of ASR. Unpublished associations between genetic polymorphisms and PPI were derived from three independent samples. In total, 120 single observations from 16 independent samples with 2660 study participants and 43 polymorphisms were included. After correction for multiple testing based on false discovery rate and considering the number of analyzed polymorphisms, significant associations were shown for four variants, even though none of these associations survived a genome-wide correction (P<5∗10-8). These results imply that PPI might be modulated by four genotypes - COMT rs4680 (primarily in males), GRIK3 rs1027599, TCF4 rs9960767, and PRODH rs385440 - indicating a role of these gene variations in the development of early information processing deficits in schizophrenia. However, the overall impact of single genes on PPI is still rather small suggesting that PPI is - like the disease phenotype - highly polygenic. Future genome-wide analyses studies with large sample sizes will enhance our understanding on the genetic architecture of PPI.

Sensorimotor gating deficits in "two-hit" models of schizophrenia risk factors

Genetic and environmental models of neuropsychiatric disease have grown exponentially over the last 20years. One measure that is often used to evaluate the translational relevance of these models to human neuropsychiatric disease is prepulse inhibition of startle (PPI), an operational measure of sensorimotor gating. Deficient PPI characterizes several neuropsychiatric disorders but has been most extensively studied in schizophrenia. It has become a useful tool in translational neuropharmacological and molecular genetics studies because it can be measured across species using almost the same experimental parameters. Although initial studies of PPI in rodents were pharmacological because of the robust predictive validity of PPI for antipsychotic efficacy, more recently, PPI has become standard common behavioral measures used in genetic and neurodevelopmental models of schizophrenia. Here we review "two hit" models of schizophrenia and discuss the utility of PPI as a tool in phenotyping these models of relevant risk factors. In the review, we consider approaches to rodent models of genetic and neurodevelopmental risk factors and selectively review "two hit" models of gene×environment and environment×environment interactions in which PPI has been measured.

Attentional functioning in individuals with 22q11 deletion syndrome: insight from ERPs

The 22q11 deletion syndrome (22q11DS), or DiGeorge syndrome (DG), is one of the most common genetic deletion syndromes. DG also carries a high risk for psychiatric disorders, with learning disabilities frequently being reported. Impairments in specific cognitive domains, such as executive functioning and attention, have also been described. The aim of this study was to investigate attentional functioning in a group of subjects with DG using ERPs, and in particular the P300 and CNV components. We studied ten patients with DG and ten healthy subjects that performed a P300 Novelty task and a CNV motor task. P3b amplitude was significantly lower in patients than in controls, while P3b latency was comparable in patients and controls. The P3a parameters were similar in both groups. All CNV amplitudes were significantly lower in DG patients than in controls. DG patients displayed slower reaction times in the CNV motor task than healthy subjects. These results point to a cognitive dysfunction related above all to executive attentional processing in DG patients. In particular, a specific difficulty emerged in selective attention and in the ability to orient and to sustain the anticipatory attention required for an executive motor response.

Cortical Development Requires Mesodermal Expression of Tbx1, a Gene Haploinsufficient in 22q11.2 Deletion Syndrome

In mammals, proper temporal control of neurogenesis and neural migration during embryonic development ensures correct formation of the cerebral cortex. Changes in the distribution of cortical projection neurons and interneurons are associated with behavioral disorders and psychiatric diseases, including schizophrenia and autism, suggesting that disrupted cortical connectivity contributes to the brain pathology. TBX1 is the major candidate gene for 22q11.2 deletion syndrome (22q11.2DS), a chromosomal deletion disorder characterized by a greatly increased risk for schizophrenia. We have previously shown that Tbx1 heterozygous mice have reduced prepulse inhibition, a behavioral abnormality that is associated with 22q11.2DS and nonsyndromic schizophrenia. Here, we show that loss of Tbx1 disrupts corticogenesis in mice by promoting premature neuronal differentiation in the medio-lateral embryonic cortex, which gives rise to the somatosensory cortex (S1). In addition, we found altered polarity in both radially migrating excitatory neurons and tangentially migrating inhibitory interneurons. Together, these abnormalities lead to altered lamination in the S1 at the terminal stages of corticogenesis in Tbx1 null mice and similar anomalies in Tbx1 heterozygous adult mice. Finally, we show that mesoderm-specific inactivation of Tbx1 is sufficient to recapitulate the brain phenotype indicating that Tbx1 exerts a cell nonautonomous role in cortical development from the mesoderm.

Persistent gating deficit and increased sensitivity to NMDA receptor antagonism after puberty in a new mouse model of the human 22q11.2 microdeletion syndrome: a study in male mice

BACKGROUND

The hemizygous 22q11.2 microdeletion is a common copy number variant in humans. The deletion confers high risk for neurodevelopmental disorders, including autism and schizophrenia. Up to 41% of deletion carriers experience psychotic symptoms.

METHODS

We present a new mouse model (Df(h22q11)/+) of the deletion syndrome (22q11.2DS) and report on, to our knowledge, the most comprehensive study undertaken to date in 22q11.2DS models. The study was conducted in male mice.

RESULTS

We found elevated postpubertal N-methyl-D-aspartate (NMDA) receptor antagonist-induced hyperlocomotion, age-independent prepulse inhibition (PPI) deficits and increased acoustic startle response (ASR). The PPI deficit and increased ASR were resistant to antipsychotic treatment. The PPI deficit was not a consequence of impaired hearing measured by auditory brain stem responses. The Df(h22q11)/+ mice also displayed increased amplitude of loudness-dependent auditory evoked potentials. Prefrontal cortex and dorsal striatal elevations of the dopamine metabolite DOPAC and increased dorsal striatal expression of the AMPA receptor subunit GluR1 was found. The Df(h22q11)/+ mice did not deviate from wild-type mice in a wide range of other behavioural and biochemical assays.

LIMITATIONS

The 22q11.2 microdeletion has incomplete penetrance in humans, and the severity of disease depends on the complete genetic makeup in concert with environmental factors. In order to obtain more marked phenotypes reflecting the severe conditions related to 22q11.2DS it is suggested to expose the Df(h22q11)/+ mice to environmental stressors that may unmask latent psychopathology.

CONCLUSION

The Df(h22q11)/+ model will be a valuable tool for increasing our understanding of the etiology of schizophrenia and other psychiatric disorders associated with the 22q11DS.

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'.

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.

[Formula: see text]Executive functioning and its relation to ASD and ADHD symptomatology in 22q11.2 deletion syndrome

Children with 22q11.2 deletion syndrome (22q11DS; velo-cardio-facial-syndrome) are at risk for the developmental disorders, attention deficit hyperactivity disorder (ADHD) and autism spectrum disorder (ASD). In this study, the relation between executive functioning (EF) and the severity of ADHD and ASD symptoms is examined, since EF is known to be important in relation to emotional and behavioral problems. The participants consist of 58 children (38 females) with a mean age of 13.5 years (SD 2.6). Standardized assessment was used to evaluate the severity of ASD and ADHD symptomatology. The major aspects of EF, i.e., cognitive flexibility, inhibition, sustained attention, distractibility, working memory and reaction speed, were evaluated. The profile of EF in 22q11DS was found to be characterized by weaker performance compared to the norms on all subdomains of EF. Poor cognitive flexibility and inhibition, as well as high distractibility, were found to be related to more severe ASD symptoms, while poor quality of sustained attention and high distractibility were found to be related to more severe ADHD symptoms. It is concluded that children with 22q11DS experience impairments in EF, and that the degree of impairment on specific EF subdomains is related to the severity of ASD and/or ADHD symptomatology. These results may help in defining the mediating role of neurocognitive dysfunctions in the development of social and behavioral problems in 22q11DS.

Tbx1: Transcriptional and Developmental Functions

Recent data have paved the way to mechanistic studies into the role of Tbx1 during development. Tbx1 is haploinsufficient and is involved in an important genetic disorder. The gene encodes a T-box transcription factor that is expressed from approximately E7.5 in mouse embryos and continues to be expressed in a highly dynamic manner. It is neither a strong transcriptional activator nor a strong repressor, but it regulates a large number of genes through epigenetic modifications. Here, we review recent literature concerning mechanisms of gene regulation by Tbx1 and its role in mammalian development, with a special focus on the cardiac, vascular, and central nervous systems.

Visual perception and processing in children with 22q11.2 deletion syndrome: associations with social cognition measures of face identity and emotion recognition

BACKGROUND

People with 22q11.2 deletion syndrome (22q11DS) have difficulty processing social information including facial identity and emotion processing. However, difficulties with visual and attentional processes may play a role in difficulties observed with these social cognitive skills.

METHODS

A cross-sectional study investigated visual perception and processing as well as facial processing abilities in a group of 49 children and adolescents with 22q11DS and 30 age and socio-economic status-matched healthy sibling controls using the Birmingham Object Recognition Battery and face processing sub-tests from the MRC face processing skills battery.

RESULTS

The 22q11DS group demonstrated poorer performance on all measures of visual perception and processing, with greatest impairment on perceptual processes relating to form perception as well as object recognition and memory. In addition, form perception was found to make a significant and unique contribution to higher order social-perceptual processing (face identity) in the 22q11DS group.

CONCLUSIONS

The findings indicate evidence for impaired visual perception and processing capabilities in 22q11DS. In turn, these were found to influence cognitive skills needed for social processes such as facial identity recognition in the children with 22q11DS.

Assessing the Cognitive Translational Potential of a Mouse Model of the 22q11.2 Microdeletion Syndrome

A chromosomal microdeletion at the 22q11.2 locus is associated with extensive cognitive impairments, schizophrenia and other psychopathology in humans. Previous reports indicate that mouse models of the 22q11.2 microdeletion syndrome (22q11.2DS) may model the genetic basis of cognitive deficits relevant for neuropsychiatric disorders such as schizophrenia. To assess the models usefulness for drug discovery, a novel mouse (Df(h22q11)/+) was assessed in an extensive battery of cognitive assays by partners within the NEWMEDS collaboration (Innovative Medicines Initiative Grant Agreement No. 115008). This battery included classic and touchscreen-based paradigms with recognized sensitivity and multiple attempts at reproducing previously published findings in 22q11.2DS mouse models. This work represents one of the most comprehensive reports of cognitive functioning in a transgenic animal model. In accordance with previous reports, there were non-significant trends or marginal impairment in some tasks. However, the Df(h22q11)/+ mouse did not show comprehensive deficits; no robust impairment was observed following more than 17 experiments and 14 behavioral paradigms. Thus - within the current protocols - the 22q11.2DS mouse model fails to mimic the cognitive alterations observed in human 22q11.2 deletion carriers. We suggest that the 22q11.2DS model may induce liability for cognitive dysfunction with additional "hits" being required for phenotypic expression.

The hippocampi of children with chromosome 22q11.2 deletion syndrome have localized anterior alterations that predict severity of anxiety

BACKGROUND

Individuals with 22q11.2 deletion syndrome (22q11.2DS) have an elevated risk for schizophrenia, which increases with history of childhood anxiety. Altered hippocampal morphology is a common neuroanatomical feature of 22q11.2DS and idiopathic schizophrenia. Relating hippocampal structure in children with 22q11.2DS to anxiety and impaired cognitive ability could lead to hippocampus-based characterization of psychosis-proneness in this at-risk population.

METHODS

We measured hippocampal volume using a semiautomated approach on MRIs collected from typically developing children and children with 22q11.2DS. We then analyzed hippocampal morphology with Localized Components Analysis. We tested the modulating roles of diagnostic group, hippocampal volume, sex and age on local hippocampal shape components. Lastly, volume and shape components were tested as covariates of IQ and anxiety.

RESULTS

We included 48 typically developing children and 69 children with 22q11.2DS in our study. Hippocampal volume was reduced bilaterally in children with 22q11.2DS, and these children showed greater variation in the shape of the anterior hippocampus than typically developing children. Children with 22q11.2DS had greater inward deformation of the anterior hippocampus than typically developing children. Greater inward deformation of the anterior hippocampus was associated with greater severity of anxiety, specifically fear of physical injury, within the 22q11.2DS group.

LIMITATIONS

Shape alterations are not specific to hippocampal subfields.

CONCLUSION

Alterations in the structure of the anterior hippocampus likely affect function and may impact limbic circuitry. We suggest these alterations potentially contribute to anxiety symptoms in individuals with 22q11.2DS through modulatory pathways. Altered hippocampal morphology may be uniquely linked to anxiety risk factors for schizophrenia, which could be a powerful neuroanatomical marker of schizophrenia risk and hence protection.

PRODH rs450046 and proline x COMT Val¹⁵⁸ Met interaction effects on intelligence and startle in adults with 22q11 deletion syndrome

RATIONALE

22q11 deletion syndrome (22q11DS) is associated with an increased risk for psychotic disorders, suggesting a relationship between genotypes and the pathophysiology of psychotic disorders. Two genes in the deleted region, catechol-O-methyl-transferase (COMT) and proline dehydrogenase (oxidase) 1 (PRODH), contain polymorphisms associated with neuropsychiatric phenotypes.

OBJECTIVES

Here, we explored the association between polymorphisms and full-scale intelligence (FSIQ), startle reactivity (SR) and prepulse inhibition (PPI) in adults with 22q11DS.

METHODS

Forty-five adults with 22q11DS were genotyped for PRODH rs450046, rs372055 and COMT Val(158)Met. Plasma proline levels, FSIQ, SR and PPI were measured.

RESULTS

Thirty-five percent of the subjects were hyperprolinemic with a median proline value of 456 μmol/L. C allele carriers of PRODH rs450046 had a lower FSIQ compared to T allele carriers, indicating the C allele to be a risk allele (C allele: mean FSIQ 60.2 (sd 8.7); T allele: mean FSIQ 73.7 (sd 11.5); F 1,43 = 7.59; p = 0.009; partial η (2) = 0.15). A significant interaction effect of proline levels and COMT Val(158)Met genotype was found for SR (F 1,16 = 7.9; p = 0.01; partial η (2) = 0.33), but not for PPI and FSIQ. In subjects with hyperprolinemia, the COMT Val(158)Met genotype effect on SR was stronger than in subjects with normal proline levels.

CONCLUSIONS

Overall, these data provide further evidence for the risk effect of elevated proline levels combined with the COMT Met allele and support the possibilities of using 22q11DS as a model to investigate genotype effects on psychiatric disorders.

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.

Pre-pulse inhibition and antisaccade performance indicate impaired attention modulation of cognitive inhibition in 22q11.2 deletion syndrome (22q11DS)

BACKGROUND

22q11.2 deletion syndrome (22q11DS) is associated with a number of physical anomalies and neuropsychological deficits including impairments in executive and sensorimotor function. It is estimated that 25% of children with 22q11DS will develop schizophrenia and other psychotic disorders later in life. Evidence of genetic transmission of information processing deficits in schizophrenia suggests performance in 22q11DS individuals will enhance understanding of the neurobiological and genetic substrates associated with information processing. In this report, we examine information processing in 22q11DS using measures of startle eyeblink modification and antisaccade inhibition to explore similarities with schizophrenia and associations with neurocognitive performance.

METHODS

Startle modification (passive and active tasks; 120- and 480-ms pre-pulse intervals) and antisaccade inhibition were measured in 25 individuals with genetically confirmed 22q11DS and 30 healthy control subjects.

RESULTS

Individuals with 22q11DS exhibited increased antisaccade error as well as some evidence (trend-level effect) of impaired sensorimotor gating during the active condition, suggesting a dysfunction in controlled attentional processing, rather than a pre-attentive dysfunction using this paradigm.

CONCLUSIONS

The findings from the present study show similarities with previous studies in clinical populations associated with 22q11DS such as schizophrenia that may indicate shared dysfunction of inhibition pathways in these groups.

The development of cognitive control in children with chromosome 22q11.2 deletion syndrome

Chromosome 22q11.2 Deletion Syndrome (22q11.2DS) is caused by the most common human microdeletion, and it is associated with cognitive impairments across many domains. While impairments in cognitive control have been described in children with 22q11.2DS, the nature and development of these impairments are not clear. Children with 22q11.2DS and typically developing children (TD) were tested on four well-validated tasks aimed at measuring specific foundational components of cognitive control: response inhibition, cognitive flexibility, and working memory. Molecular assays were also conducted in order to examine genotype of catechol-O-methyltransferase (COMT), a gene located within the deleted region in 22q11.2DS and hypothesized to play a role in cognitive control. Mixed model regression analyses were used to examine group differences, as well as age-related effects on cognitive control component processes in a cross-sectional analysis. Regression models with COMT genotype were also conducted in order to examine potential effects of the different variants of the gene. Response inhibition, cognitive flexibility, and working memory were impaired in children with 22q11.2DS relative to TD children, even after accounting for global intellectual functioning (as measured by full-scale IQ). When compared with TD individuals, children with 22q11.2DS demonstrated atypical age-related patterns of response inhibition and cognitive flexibility. Both groups demonstrated typical age-related associations with working memory. The results of this cross-sectional analysis suggest a specific aberration in the development of systems mediating response inhibition in a sub-set of children with 22q11.2DS. It will be important to follow up with longitudinal analyses to directly examine these developmental trajectories, and correlate neurocognitive variables with clinical and adaptive outcome measures.

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".

Common and specific impairments in attention functioning in girls with chromosome 22q11.2 deletion, fragile X or Turner syndromes

Background

Chromosome 22q11.2 deletion syndrome (22q11.2DS), fragile X syndrome (FXS), and Turner syndrome (TS) are complex and variable developmental syndromes caused by different genetic abnormalities; yet, they share similar cognitive impairments in the domains of numbers, space, and time. The atypical development of foundational neural networks that underpin the attentional system is thought to result in further impairments in higher-order cognitive functions. The current study investigates whether children with similar higher-order cognitive impairments but different genetic disorders also show similar impairments in alerting, orienting, and executive control of attention.

Methods

Girls with 22q11.2DS, FXS, or TS and typically developing (TD) girls, aged 7 to 15 years, completed an attention network test, a flanker task with alerting and orienting cues. Exploration of reaction times and accuracy allowed us to test for potential commonalities in attentional functioning in alerting, orienting, and executive control. Linear regression models were used to test whether the predictors of group and chronological age were able to predict differences in attention indices.

Results

Girls with 22q11.2DS, FXS, or TS demonstrated unimpaired function of the alerting system and impaired function of the executive control system. Diagnosis-specific impairments were found such that girls with FXS made more errors and had a reduced orienting index, while girls with 22q11.2DS showed specific age-related deficits in the executive control system.

Conclusions

These results suggest that the control but not the implementation of attention is selectively impaired in girls with 22q11.2DS, TS or FXS. Additionally, the age effect on executive control in girls with 22q11.2DS implies a possible altered developmental trajectory.

The 22q11.2 deletion syndrome as a window into complex neuropsychiatric disorders over the lifespan

Evidence is rapidly accumulating that rare, recurrent copy number variants represent large effect risk factors for neuropsychiatric disorders. 22q11.2 deletion syndrome (22q11DS) (velocardiofacial syndrome or DiGeorge syndrome) is the most common known contiguous gene deletion syndrome and is associated with diverse neuropsychiatric disorders across the life span. One of the most intriguing aspects of the syndrome is the variability in clinical and cognitive presentation: children with 22q11DS have high prevalence of autism spectrum, attention deficit, and anxiety disorders, as well as psychotic-like features, and up to 30% of adolescents and adults develop schizophrenia-like psychosis. Recently, cases of early-onset Parkinson's disease in adults have been reported, collectively suggesting a role for disrupted dopaminergic neurotransmission in the observed neuropsychiatric phenotypes. There is also some evidence that 22q11DS-associated autism spectrum disorder and schizophrenia represent two unrelated phenotypic manifestations, consistent with a neuropsychiatric pleiotropy model. This genetic lesion thus provides a unique model for the discovery of specific genomic risk and (potentially) protective factors for neuropsychiatric disease. Here, we provide an overview of neuropsychiatric findings to date, which highlight the value of this syndrome in mapping the developmental trajectory of dimensional phenotypes that traverse multiple diagnostic categories. Potential sources of genetic variability that may contribute to the disorder's heterogeneous presentation are reviewed. Because of its known genetic etiology, animal models can readily be developed that recapitulate specific aspects of the syndrome. Future research directions involve translational models and potential for drug screenable targets in the context of this human model system.

Hearing loss in a mouse model of 22q11.2 Deletion Syndrome

22q11.2 Deletion Syndrome (22q11DS) arises from an interstitial chromosomal microdeletion encompassing at least 30 genes. This disorder is one of the most significant known cytogenetic risk factors for schizophrenia, and can also cause heart abnormalities, cognitive deficits, hearing difficulties, and a variety of other medical problems. The Df1/+ hemizygous knockout mouse, a model for human 22q11DS, recapitulates many of the deficits observed in the human syndrome including heart defects, impaired memory, and abnormal auditory sensorimotor gating. Here we show that Df1/+ mice, like human 22q11DS patients, have substantial rates of hearing loss arising from chronic middle ear infection. Auditory brainstem response (ABR) measurements revealed significant elevation of click-response thresholds in 48% of Df1/+ mice, often in only one ear. Anatomical and histological analysis of the middle ear demonstrated no gross structural abnormalities, but frequent signs of otitis media (OM, chronic inflammation of the middle ear), including excessive effusion and thickened mucosa. In mice for which both in vivo ABR thresholds and post mortem middle-ear histology were obtained, the severity of signs of OM correlated directly with the level of hearing impairment. These results suggest that abnormal auditory sensorimotor gating previously reported in mouse models of 22q11DS could arise from abnormalities in auditory processing. Furthermore, the findings indicate that Df1/+ mice are an excellent model for increased risk of OM in human 22q11DS patients. Given the frequently monaural nature of OM in Df1/+ mice, these animals could also be a powerful tool for investigating the interplay between genetic and environmental causes of OM.

Copy number variation at 22q11.2: from rare variants to common mechanisms of developmental neuropsychiatric disorders

Recently discovered genome-wide rare copy number variants (CNVs) have unprecedented levels of statistical association with many developmental neuropsychiatric disorders, including schizophrenia, autism spectrum disorders, intellectual disability and attention deficit hyperactivity disorder. However, as CNVs often include multiple genes, causal genes responsible for CNV-associated diagnoses and traits are still poorly understood. Mouse models of CNVs are in use to delve into the precise mechanisms through which CNVs contribute to disorders and associated traits. Based on human and mouse model studies on rare CNVs within human chromosome 22q11.2, we propose that alterations of a distinct set of multiple, noncontiguous genes encoded in this chromosomal region, in concert with modulatory impacts of genetic background and environmental factors, variably shift the probabilities of phenotypes along a predetermined developmental trajectory. This model can be further extended to the study of other CNVs and may serve as a guide to help characterize the impact of genes in developmental neuropsychiatric disorders.

Schizophrenia-like neurophysiological abnormalities in 22q11.2 deletion syndrome and their association to COMT and PRODH genotypes

22q11.2 deletion syndrome (22q11.2DS) is a common genetic risk factor for the development of schizophrenia. We investigated two neurophysiological endophenotypes of schizophrenia - P50 sensory gating and mismatch negativity in 22q11.2DS subject and evaluated their association with catechol O-methyltransferase (COMT) and proline dehydrogenase (PRODH) genetic variants. We also assessed the association of neurophysiological measures with schizophrenia-like symptomatology in 22q11.2DS. Fifty-nine subjects, 41 with 22q11.2DS and 18 typically developing controls, participated in the study. The participants with 22q11.2DS were genotyped for the COMT Val(158)Met (rs4680) and PRODH Gln(19)Pro (rs2008720) and Arg(185)Trp (rs4819756) polymorphisms. Following psychiatric evaluation, all the participants underwent neurophysiological recordings and executive function assessment. The 22q11.2DS group showed poorer sensory gating of the P50 response than the controls. Within the 22q11.2DS group, the COMT Met allele was associated with poorer sensory gating, while both the COMT Met allele and the PRODH Pro-Arg haplotype were associated with smaller mismatch negativity amplitudes. Smaller mismatch negativity amplitudes predicted greater impairment of executive functions and greater severity of schizophrenia-like negative symptoms in 22q11.2DS. The current study demonstrates that sensory gating impairments that are typical of schizophrenia are found in 22q11.2DS subjects. Our results further suggest that COMT and PRODH genetic variations contribute to sensory gating and mismatch negativity schizophrenia-like impairments in 22q11.2DS, possibly via dopaminergic/glutamatergic networks. The associations of mismatch negativity impairments with increased severity of schizophrenia-like negative symptoms and poorer executive functions performance in our 22q11.2DS sample suggest that mismatch negativity is a potential endophenotype for schizophrenia in 22q11.2DS.

Forebrain gene expression predicts deficits in sensorimotor gating after isolation rearing in male rats

Compared to socially housed (SH) rats, adult isolation-reared (IR) rats exhibit phenotypes relevant to schizophrenia (SZ), including reduced prepulse inhibition (PPI) of startle. PPI is normally regulated by the medial prefrontal cortex (mPFC) and nucleus accumbens (NAC). We assessed PPI, auditory-evoked local field potentials (LFPs) and expression of seven PPI- and SZ-related genes in the mPFC and NAC, in IR and SH rats. Buffalo (BUF) rats were raised in same-sex groups of 2-3 (SH) or in isolation (IR). PPI was measured early (d53) and later in adulthood (d74); LFPs were measured approximately on d66. Brains were processed for RT-PCR measures of mPFC and NAC expression of Comt, Erbb4, Grid2, Ncam1, Slc1a2, Nrg1 and Reln. Male IR rats exhibited PPI deficits, most pronounced at d53; male and female IR rats had significantly elevated startle magnitude on both test days. Gene expression levels were not significantly altered by IR. PPI levels (d53) were positively correlated with mPFC expression of several genes, and negatively correlated with NAC expression of several genes, in male IR but not SH rats. Late (P90) LFP amplitudes correlated significantly with expression levels of 6/7 mPFC genes in male rats, independent of rearing. After IR that disrupts early adult PPI in male BUF rats, expression levels of PPI- and SZ-associated genes in the mPFC correlate positively with PPI, and levels in the NAC correlate negatively with PPI. These results support the model that specific gene-behavior relationships moderate the impact of early-life experience on SZ-linked behavioral and neurophysiological markers.

Coupling of gene expression in medial prefrontal cortex and nucleus accumbens after neonatal ventral hippocampal lesions accompanies deficits in sensorimotor gating and auditory processing in rats

BACKGROUND

After neonatal ventral hippocampal lesions (NVHLs), adult rats exhibit evidence of neural processing deficits relevant to schizophrenia, including reduced prepulse inhibition (PPI) of acoustic startle and impaired sensory processing. In intact rats, the regulation of PPI by the ventral hippocampus (VH) is mediated via interactions with medial prefrontal cortex (mPFC) and nucleus accumbens (NAC). We assessed PPI, auditory-evoked responses and expression of 7 schizophrenia-related genes in mPFC and NAC, in adult rats after sham- or real NVHLs.

METHODS

Male inbred Buffalo (BUF) rat pups (d7; n=36) received either vehicle or ibotenic acid infusion into the VH. PPI and auditory-evoked dentate gyrus local field potentials (LFPs) were measured on d56 and d66, respectively. Brains were processed for RT-PCR measures of mPFC and NAC Comt, Erbb4, Grid2, Ncam1, Slc1a2, Nrg1 and Reln.

RESULTS

NVHL rats exhibited significant deficits in PPI (p=0.005) and LFPs (p<0.015) proportional to lesion size. Sham vs. NVHL rats did not differ in gene expression levels in mPFC or NAC. As we previously reported, multiple gene expression levels were highly correlated within- (mean r's≈0.5), but not across-brain regions (mean r's≈0). However, for three genes--Comt, Slc1a2 and Ncam1--after NVHLs, expression levels became significantly correlated, or "coupled," across the mPFC and NAC (p's<0.03, 0.002 and 0.05, respectively), and the degree of "coupling" increased with VH lesion size.

CONCLUSIONS

After NVHLs that disrupt PPI and auditory processing, specific gene expression levels suggest an abnormal functional coupling of the mPFC and NAC. This model of VH-mPFC-NAC network dysfunction after NVHLs may have implications for understanding the neural basis for PPI- and related sensory processing deficits in schizophrenia patients.

Exploring a neurogenic basis of velopharyngeal dysfunction in Tbx1 mutant mice: no difference in volumes of the nucleus ambiguus

OBJECTIVE

Velopharyngeal hypotonia seems to be an important factor in velopharyngeal dysfunction in 22q11.2 deletion syndrome, but the etiology is not understood. Because TBX1 maps within the typical 22q11.2 deletion and Tbx1-deficient mice phenocopy many findings in patients with the 22q11.2 deletion syndrome, TBX1 is considered the major candidate gene in the etiology of these defects. Tbx1 heterozygosity in mice results in abnormal vocalization 7 days postnatally, suggestive of velopharyngeal dysfunction. Previous case-control studies on muscle specimens from patients and mice revealed no evidence for a myogenic cause of velopharyngeal dysfunction. Velopharyngeal muscles are innervated by cranial nerves that receive signals from the nucleus ambiguus in the brainstem. In this study, a possible neurogenic cause underlying velopharyngeal dysfunction in Tbx1 heterozygous mice was explored by determining the size of the nucleus ambiguus in Tbx1 heterozygous and wild type mice.

METHODS

The cranial motor nuclei in the brainstems of postnatal day 7 wild type (n=4) and Tbx1 heterozygous (n=4) mice were visualized by in situ hybridization on transverse sections to detect Islet-1 mRNA, a transcription factor known to be expressed in motor neurons. The volumes of the nucleus ambiguus were calculated.

RESULTS

No substantial histological differences were noted between the nucleus ambiguus of the two groups. Tbx1 mutant mice had mean nucleus ambiguus volumes of 4.6 million μm(3) (standard error of the mean 0.9 million μm(3)) and wild type mice had mean volumes of 3.4 million μm(3) (standard error of the mean 0.6 million μm(3)). Neither the difference nor the variance between the means were statistically significant (t-test p=0.30, Levene's test p=0.47, respectively).

CONCLUSIONS

Based on the histology, there is no difference or variability between the volumes of the nucleus ambiguus of Tbx1 heterozygous and wild type mice. The etiology of velopharyngeal hypotonia and variable speech in children with 22q11.2 deletion syndrome warrants further investigation.

Converging levels of analysis on a genomic hotspot for psychosis: insights from 22q11.2 deletion syndrome

Schizophrenia is a devastating neurodevelopmental disorder that, despite extensive research, still poses a considerable challenge to attempts to unravel its heterogeneity, and the complex biochemical mechanisms by which it arises. While the majority of cases are of unknown etiology, accumulating evidence suggests that rare genetic mutations, such as 22q11.2 Deletion Syndrome (22qDS), can play a significant role in predisposition to the illness. Up to 25% of individuals with 22qDS eventually develop schizophrenia; conversely, this deletion is estimated to account for 1-2% of schizophrenia cases overall. This locus of Chromosome 22q11.2 contains genes that encode for proteins and enzymes involved in regulating neurotransmission, neuronal development, myelination, microRNA processing, and post-translational protein modifications. As a consequence of the deletion, affected individuals exhibit cognitive dysfunction, structural and functional brain abnormalities, and neurodevelopmental anomalies that parallel many of the phenotypic characteristics of schizophrenia. As an illustration of the value of rare, highly penetrant genetic subtypes for elucidating pathological mechanisms of complex neuropsychiatric disorders, we provide here an overview of the cellular, network, and systems-level anomalies found in 22qDS, and review the intriguing evidence for this disorder's association with schizophrenia. This article is part of the Special Issue entitled 'Neurodevelopmental Disorders'.

Prepulse inhibition in psychiatric disorders--apart from schizophrenia

Prepulse inhibition (PPI) is a robust operational measure of sensorimotor gating. In schizophrenic patients PPI is deficient. The aim of our review was to investigate the state of science regarding PPI and psychiatric disorders aside from schizophrenia. We used the online database PubMed in order to search for original published reports on PPI studies. The terms "prepulse inhibition", "sensorimotor gating", "blink recovery", and "blink reflex excitability" have been combined with the names of psychiatric disorders. We found that PPI is deficient in obsessive compulsive disorder (OCD) and Gilles de la Tourette's syndrome (GTS). In bipolar disorder dysfunctional PPI seems to be rather state dependent. Studies on depression and attention deficit/hyperactivity disorder (ADHD) consistently report no alterations. Evidence regarding sensorimotor gating in anxiety, autism, fragile X syndrome, posttraumatic stress disorder (PTSD), substance disorders, and Huntington's disease is still poor. There is a strong need for further studies on PPI in psychiatric disorders. PPI is highly applicable for translational research and might also be a very useful tool to investigate the mode of action of innovative, neuro-modulative techniques. Future PPI studies should control for influencing variables such as smoking, sex, or medication.

A cross-sectional analysis of the development of response inhibition in children with chromosome 22q11.2 deletion syndrome

Chromosome 22q11.2 deletion syndrome (22q11.2DS) is a neurogenetic disorder that is associated with cognitive impairments and significantly elevated risk for developing schizophrenia. While impairments in response inhibition are central to executive dysfunction in schizophrenia, the nature and development of such impairments in children with 22q11.2DS, a group at high risk for the disorder, are not clear. Here we used a classic Go/No-Go paradigm to quantify proactive (anticipatory stopping) and reactive (actual stopping) response inhibition in 47 children with 22q11.2DS and 36 typically developing (TD) children, all ages 7-14. A cross-sectional design was used to examine age-related associations with response inhibition. When compared with TD individuals, children with 22q11.2DS demonstrated typical proactive response inhibition at all ages. By contrast, reactive response inhibition was impaired in children with 22q11.2DS relative to TD children. While older age predicted better reactive response inhibition in TD children, there was no age-related association with reactive response inhibition in children with 22q11.2DS. Closer examination of individual performance data revealed a wide range of performance abilities in older children with 22q11.2DS; some typical and others highly impaired. The results of this cross-sectional analysis suggest an impaired developmental trajectory of reactive response inhibition in some children with 22q11.2DS that might be related to atypical development of neuroanatomical systems underlying this cognitive process. As part of a larger study, this investigation might help identify risk factors for conversion to schizophrenia and lead to early diagnosis and preventive intervention.

Fronto-temporal-mesolimbic gene expression and heritable differences in amphetamine-disrupted sensorimotor gating in rats

RATIONALE

Differences in sensitivity to the prepulse inhibition (PPI)-disruptive effects of D2-family agonists in Sprague-Dawley (SD) vs. Long Evans (LE) rats are heritable, reflect differential activation of DA signaling in the nucleus accumbens (NAC), and are associated with differences in expression of specific NAC genes. These differences may inform us about the biology of PPI deficits in disorders such as schizophrenia.

OBJECTIVES

After confirming these strain-based PPI differences, we measured expression of four genes in NAC and other regions that regulate PPI: medial prefrontal cortex and ventral hippocampus (VH).

METHODS

Startle and PPI were assessed in SD and LE rats administered D-amphetamine (0 vs. 4.5 mg/kg, sc). Two weeks later, brain tissue was processed for comt, nrg1, grid2, and csnk1e expression; blood comt expression was also tested.

RESULTS

Data confirmed expected PPI phenotypes. Gene expression levels differed across strains, sexes, and brain regions, with LE > SD expression in most genes and regions, and female > male expression for all NAC genes. Within any brain region, expression of the four genes was highly inter-correlated; across regions, correlations were less robust, reflecting distinct strain- or sex-based subgroups. PPI amphetamine sensitivity at 120 ms correlated significantly with NAC nrg1 expression, while amphetamine sensitivity for 30 ms PPI and startle magnitude correlated significantly with VH nrg1 and blood comt expression.

CONCLUSIONS

Rat strains differing in a schizophrenia-linked phenotype also differ in expression levels of genes associated both with that phenotype, and with schizophrenia, within brain regions associated with that phenotype and schizophrenia.

Startle reactivity and prepulse inhibition of the acoustic startle response are modulated by catechol-O-methyl-transferase Val(158) Met polymorphism in adults with 22q11 deletion syndrome

22q11 deletion syndrome (22q11DS) is a genetic disorder caused by a microdeletion on chromosome 22, which includes the gene coding for catechol-O-methyl-transferase (COMT). High dopamine (DA) levels due to COMT haplo-insufficiency may be associated with the increased risk of developing schizophrenia in adults with 22q11DS. Reduced prepulse inhibition (PPI) of the acoustic startle response has been associated with schizophrenia and with disrupted DAergic transmission in the prefrontal cortex (PFC). COMT Val(158)Met polymorphism has been shown to influence PPI. We report the first study in adults with 22q11DS to examine PPI of the acoustic startle response and its modulation by COMT Val(158)Met polymorphism. Startle reactivity (SR) and PPI of the acoustic startle response were measured in 23 adults with 22q11DS and 21 healthy controls. 22q11DS subjects were genotyped for the functional COMT Val(158)Met polymorphism. 22q11DS Met hemizygotes showed reduced SR and PPI compared with 22q11DS Val hemizygotes. The effect of COMT Val(158)Met polymorphism on PPI was no longer significant when controlling for baseline SR. Met hemizygosity in 22q11DS is associated with reduced SR and influences PPI indirectly. Decreased PFC functioning following excessive PFC DA levels may be one of the mechanisms by which the Met genotype in 22q11DS disrupts SR.

Update: studies of prepulse inhibition of startle, with particular relevance to the pathophysiology or treatment of Tourette Syndrome

Prepulse inhibition of the startle reflex (PPI) is an operational measure of sensorimotor gating, in which the motor response to an abrupt, intense stimulus is inhibited by a weak lead stimulus. PPI is reduced in several brain disorders, including Tourette Syndrome (TS); it is regulated by forebrain circuitry, including portions of the basal ganglia implicated in the pathophysiology of TS, and is also heritable and under strong genetic control. PPI has been the focus of numerous translational models, because it is expressed by most mammalian species, with remarkable conservation of response characteristics and underlying neural circuitry between rodents and primates. Several of these models have recently explored causative factors in TS - from genes to specific basal ganglia perturbations - as well as potential TS therapeutics, including novel pharmacological and neurosurgical interventions. With the focus on Comprehensive Behavioral Interventions for Tics (CBIT) in the evolving treatment model for TS, future studies might apply PPI as a predictive measure for CBIT response, or for identifying medications that might augment CBIT efficacy. In the end, a measure based on a simple pontine-based reflex will have limitations in its ability to explicate any complex behavioral phenotype.

MicroRNA dysregulation in neuropsychiatric disorders and cognitive dysfunction

MicroRNAs (miRNA), a class of non-coding RNAs, are emerging as important modulators of neuronal development, structure and function. A connection has been established between abnormalities in miRNA expression and miRNA-mediated gene regulation and psychiatric and neurodevelopmental disorders as well as cognitive dysfunction. Establishment of this connection has been driven by progress in elucidating the genetic etiology of these phenotypes and has provided a context to interpret additional supporting evidence accumulating from parallel expression profiling studies in brains and peripheral blood of patients. Here we review relevant evidence that supports this connection and explore possible mechanisms that underlie the contribution of individual miRNAs and miRNA-related pathways to the pathogenesis and pathophysiology of these complex clinical phenotypes. The existing evidence provides useful hypotheses for further investigation as well as important clues for identifying novel therapeutic targets.

Occurrence of affective disorders compared to other psychiatric disorders in children and adolescents with 22q11.2 deletion syndrome

BACKGROUND

22q11.2 deletion syndrome (22qDS) is a common genetic disorder with highly variable clinical manifestations that may include depression, bipolar disorder and schizophrenia. Studies of psychiatric disorders in youth with 22qDS often had methodological limitations. This study reviewed clinical studies with the currently best available methodology to determine the occurrence of affective disorders compared to other psychiatric disorders in youth with 22qDS.

METHOD

A PubMed search was performed to identify psychiatric studies published from 2000 through 2009 of children and adolescents with genetically confirmed 22qDS who underwent systematic psychiatric assessments. Studies that met defined inclusion/exclusion criteria were selected for further analysis.

RESULTS

Seven studies with a total of 323 children and adolescents with 22qDS (mean age=10.8 years) met the defined inclusion/exclusion criteria. Depressive disorders, but not bipolar spectrum disorders, were increased compared to community-based rates in youth without 22qDS. Anxiety disorders and attention-deficit/hyperactivity disorder were the most frequent disorders. Although psychotic-like phenomena and schizotypical traits were reported, only two adolescents (<1%) had a psychotic disorder.

LIMITATIONS

Unknown selection and assessment factors may have impacted on occurrence rates.

CONCLUSION

The elevated occurrence of depressive, anxiety, and attention disorders in children with 22qDS, compared to community-based rates in children without 22qDS, suggest that psychiatric screening is needed. Longitudinal study is needed to determine if these childhood psychiatric disorders will resolve, continue into adulthood, or develop into more serious psychopathology.

Mouse Models of 22q11.2-Associated Autism Spectrum Disorder

Copy number variation (CNV) of human chromosome 22q11.2 is associated with an elevated rate of autism spectrum disorder (ASD) and represents one of syndromic ASDs with rare genetic variants. However, the precise genetic basis of this association remains unclear due to its relatively large hemizygous and duplication region, including more than 30 genes. Previous studies using genetic mouse models suggested that although not all 22q11.2 genes contribute to ASD symptomatology, more than one 22q11.2 genes have distinct phenotypic targets for ASD symptoms. Our data show that deficiency of the two 22q11.2 genesTbx1 and Sept5 causes distinct phenotypic sets of ASD symptoms.

Prepulse inhibition of startle response: recent advances in human studies of psychiatric disease

Prepulse inhibition (PPI) is considered to be one of the most promising neurophysiological indexes for translational research in psychiatry. Impairment of PPI has been reported in several psychiatric diseases, particularly schizophrenia, where PPI is considered a candidate intermediate phenotype (endophenotype) of the disease. Recent findings from a variety of research areas have provided important evidence regarding PPI impairment. Human brain imaging studies have demonstrated the involvement of the striatum, hippocampus, thalamus and frontal and parietal cortical regions in PPI. In addition, several genetic polymorphisms, including variations in the genes coding for Catechol O-methyltransferase, Neuregulin 1, nuclear factor kappa-B subunit 3 and serotonin-2A receptor were related to PPI; and these findings support PPI as a polygenetic trait that involves several neurotransmitter pathways. Early psychosis studies suggest that PPI disruption is present before the onset of psychosis. Also, discrepancy of PPI impairment between children and adults can be found in other psychiatric diseases, such as autistic spectrum disorders and posttraumatic stress disorder, and comprehensive investigation of startle response might contribute to understand the impairment of the neural circuitry in psychiatric diseases. Finally, recent studies with both Asian and Caucasian subjects indicate that patients with schizophrenia exhibit impaired PPI, and impaired sensorimotor gating might be a global common psychophysiological feature of schizophrenia. In conclusion, studies of PPI have successfully contributed to a better understanding of the fundamental neural mechanisms underlying sensorimotor gating and will certainly be most valuable in devising future approaches that aim to investigate the complex pathogenesis of psychiatric diseases.

Blast-induced tinnitus and hearing loss in rats: behavioral and imaging assays

Abstract The current study used a rat model to investigate the underlying mechanisms of blast-induced tinnitus, hearing loss, and associated traumatic brain injury (TBI). Seven rats were used to evaluate behavioral evidence of tinnitus and hearing loss, and TBI using magnetic resonance imaging following a single 10-msec blast at 14 psi or 194 dB sound pressure level (SPL). The results demonstrated that the blast exposure induced early onset of tinnitus and central hearing impairment at a broad frequency range. The induced tinnitus and central hearing impairment tended to shift towards high frequencies over time. Hearing threshold measured with auditory brainstem responses also showed an immediate elevation followed by recovery on day 14, coinciding with behaviorally-measured results. Diffusion tensor magnetic resonance imaging results demonstrated significant damage and compensatory plastic changes to certain auditory brain regions, with the majority of changes occurring in the inferior colliculus and medial geniculate body. No significant microstructural changes found in the corpus callosum indicates that the currently adopted blast exposure mainly exerts effects through the auditory pathways rather than through direct impact onto the brain parenchyma. The results showed that this animal model is appropriate for investigation of the mechanisms underlying blast-induced tinnitus, hearing loss, and related TBI. Continued investigation along these lines will help identify pathology with injury/recovery patterns, aiding development of effective treatment strategies.

Cognitive phenotype of velocardiofacial syndrome: a review

The behavioural phenotype of velocardiofacial syndrome (VCFS), one of the most common human multiple anomaly syndromes, includes developmental disabilities, frequently including intellectual disability (ID) and high risk of diagnosis of psychotic disorders including schizophrenia. VCFS may offer a model of the relationship between ID and risk of major mental health difficulties. This paper reviews literature on the cognitive phenotype and its relationship with a polymorphism of the gene coding for catechol O-methyltransferase (COMT), a gene haploinsufficient in VCFS which modulates prefrontal dopamine levels. Principal features of the variable cognitive phenotype of VCFS in young people are ID, superiority of verbal over performance I.Q. and verbal over visuospatial memory, and difficulties with number and object magnitude comparisons, time perception and memory for serial order, and orienting of attention. Despite some improvements with age, problems with higher order attentional tasks involving planning persist, possibly modulated by COMT activity levels. Candidate cognitive endophenotypes include problems with retrieval of contextual information from memory and in executive control and focussing of attention. Longitudinal research using common core batteries of psychometric assessments, and experimental measures of cognitive function capable of direct translation for use with animal models, will further advance understanding of the developmental dynamics of VCFS.

Avoiding mouse traps in schizophrenia genetics: lessons and promises from current and emerging mouse models

Schizophrenia is one of the most common psychiatric disorders, but despite progress in identifying the genetic factors implicated in its development, the mechanisms underlying its etiology and pathogenesis remain poorly understood. Development of mouse models is critical for expanding our understanding of the causes of schizophrenia. However, translation of disease pathology into mouse models has proven to be challenging, primarily due to the complex genetic architecture of schizophrenia and the difficulties in the re-creation of susceptibility alleles in the mouse genome. In this review we highlight current research on models of major susceptibility loci and the information accrued from their analysis. We describe and compare the different approaches that are necessitated by diverse susceptibility alleles, and discuss their advantages and drawbacks. Finally, we discuss emerging mouse models, such as second-generation pathophysiology models based on innovative approaches that are facilitated by the information gathered from the current genetic mouse models.