The neural correlates of non-spatial working memory in velocardiofacial syndrome (22q11.2 deletion syndrome)

Extent of magnitude representation deficit and relationship with arithmetic skills in children with 22q11.2DS

BACKGROUND

Previous studies have produced conflicting results concerning the extent of magnitude representation deficit and its relationship with arithmetic achievement in children with 22q11.2 deletion syndrome. More specifically, it remains unclear whether deficits are restricted to visuospatial content or are more general and whether they could explain arithmetical impairment.

METHODS

Fifteen 5- to 12-year-old children with 22q11.2 deletion syndrome and 23 age-matched healthy controls performed a non-symbolic magnitude comparison task. Depending on the trial, participants had to compare stimuli with high or low visuospatial load (visuospatial stimuli or temporal sequence of visual stimuli). The participants also completed a battery of arithmetic skills (ZAREKI-R) and a battery of global cognitive functioning (WISC-V or WPPSI-IV), from which working memory and visuospatial indices were derived.

RESULTS

Children with 22q11.2DS responded as fast as healthy controls did but received fewer correct responses, irrespective of visuospatial load. In addition, their performance in the non-symbolic magnitude comparison task did not correlate with the ZAREKI total score, while the working memory index did.

CONCLUSION

Children with 22q11.2DS might suffer from a global magnitude representation deficit rather than a specific deficit due to visuospatial load. However, this deficit alone does not seem to be related to arithmetic achievement. Working memory might be a better concern of interest in favoring arithmetic skills in patients with 22q11.2 deletion syndrome.

TRIAL REGISTRATION

Clinicaltrials, NCT04373226 . Registered 16 September 2020.

Executive functioning in preschoolers with 22q11.2 deletion syndrome and the impact of congenital heart defects

BACKGROUND

Executive functioning (EF) is an umbrella term for various cognitive functions that play a role in monitoring and planning to effectuate goal-directed behavior. The 22q11.2 deletion syndrome (22q11DS), the most common microdeletion syndrome, is associated with a multitude of both somatic and cognitive symptoms, including EF impairments in school-age and adolescence. However, results vary across different EF domains and studies with preschool children are scarce. As EF is critically associated with later psychopathology and adaptive functioning, our first aim was to study EF in preschool children with 22q11DS. Our second aim was to explore the effect of a congenital heart defects (CHD) on EF abilities, as CHD are common in 22q11DS and have been implicated in EF impairment in individuals with CHD without a syndromic origin.

METHODS

All children with 22q11DS (n = 44) and typically developing (TD) children (n = 81) were 3.0 to 6.5 years old and participated in a larger prospective study. We administered tasks measuring visual selective attention, visual working memory, and a task gauging broad EF abilities. The presence of CHD was determined by a pediatric cardiologist based on medical records.

RESULTS

Analyses showed that children with 22q11DS were outperformed by TD peers on the selective attention task and the working memory task. As many children were unable to complete the broad EF task, we did not run statistical analyses, but provide a qualitative description of the results. There were no differences in EF abilities between children with 22q11DS with and without CHDs.

CONCLUSION

To our knowledge, this is the first study measuring EF in a relatively large sample of young children with 22q11DS. Our results show that EF impairments are already present in early childhood in children with 22q11DS. In line with previous studies with older children with 22q11DS, CHDs do not appear to have an effect on EF performance. These findings might have important implications for early intervention and support the improvement of prognostic accuracy.

Age-Related Improvements in Executive Functions and Focal Attention in 22q11.2 Deletion Syndrome Vary Across Domain and Task

OBJECTIVE

Executive functions (EF) and focal attention have been identified as a weakness in the profile of 22q11.2 deletion syndrome (22q11DS). However, due to a high variety of tasks used across previous studies, it remains unclear whether impairments may be more pronounced for specific subdomains of EF and focal attention. Furthermore, age-related changes have only been examined in a few studies, so far only yielding a partial view of the overall developmental profile.

METHOD

In a broad age range (8-35 years) composed of longitudinal data, 183 participants (103 diagnosed with 22q11DS) completed an extensive assessment of EF and attention. To get a more comprehensive overview of specific versus global impairments, several tasks were assessed within multiple domains.

RESULTS

Results suggest differential impairments and trajectories in specific EF subdomains. Specifically, our findings suggest that individuals with 22q11DS not only showed lower overall inhibition skills, but also that initiation skills developed at a slower pace compared to healthy controls. Results are less clear regarding cognitive flexibility, updating and focal attention, for which performance strongly depended on the tasks that was selected to assess the domain.

CONCLUSIONS

Findings confirm and extend knowledge on differential developmental patterns of EF and attention domains in 22q11DS. They further stress the necessity to administer extensive, multifaceted evaluations to gain a more reliable overview of patients' cognitive profile.

Upregulation of DGCR8, a Candidate Predisposing to Schizophrenia in Han Chinese, Contributes to Phenotypic Deficits and Neuronal Migration Delay

DiGeorge Syndrome Critical Region Gene 8 (DGCR8) is a key component of the microprocessor complex governing the maturation of most microRNAs, some of which participate in schizophrenia and neural development. Previous studies have found that the 22q11.2 locus, containing DGCR8, confers a risk of schizophrenia. However, the role of DGCR8 in schizophrenia and the early stage of neural development has remained unknown. In the present study, we try to identify the role of DGCR8 in schizophrenia from human samples and animal models. We found that the G allele and GG genotype of rs3757 in DGCR8 conferred a higher risk of schizophrenia, which likely resulted from higher expression of DGCR8 according to our test of dual-luciferase reporter system. Employed overexpression model in utero and adult mice, we also revealed that the aberrant increase of Dgcr8 delayed neuronal migration during embryological development and consequently triggered abnormal behaviors in adult mice. Together, these results demonstrate that DGCR8 may play a role in the etiology of schizophrenia through regulating neural development.

From Learning to Memory: A Comparison Between Verbal and Non-verbal Skills in 22q11.2 Deletion Syndrome

Background: Previous studies on possible memory deficits in 22q11DS often focused on quantifying the information memorized, whereas learning processes have been mostly overlooked. Furthermore, methodological differences in task design have made verbal and non-verbal comparison challenging and mixed results have been observed depending on chosen stimuli. Method: 135 participants (78 with 22q11DS) completed a multi-trial memory task modeled after the Rey Auditory Verbal Learning Task, comparing verbal and non-verbal learning as well as retention over time. Performance in the 22q11DS group were compared to controls and learning curves were analyzed. Results: In 22q11DS, slower acquisition of non-verbal material and higher rates of errors in both verbal and non-verbal tasks was observed. After 30 min, free recall performance, when corrected for initial learning rate, was similar between 22q11DS and controls. Conversely, recognition performance was overall weaker for 22q11DS in both modalities (verbal and non-verbal). Conclusion: This study examined how information is acquired, retained in memory over time and how different recall modalities (free recall vs. recognition) could yield different performances. Clinical implications of the findings are discussed.

Working Memory Impairments in Cerebellar Disorders of Childhood

The cerebellum is a crucial center for motor control and integration. Increasing evidence supports the notion that the cerebellum is also involved in nonmotor functions. Along these lines, multiple cerebellar disorders of childhood and adulthood are associated with behavioral and cognitive symptoms, including impairments in memory. One form of memory commonly affected in cerebellar disorders is working memory, which uses attention to manipulate information that is immediately available to execute cognitive tasks. This article reviews the literature illustrating that working memory impairments are frequently observed in acquired, congenital, and genetic/developmental cerebellar disorders of childhood. Functional neuroimaging studies demonstrate that working memory tasks engage many posterior regions of the cerebellar hemispheres and vermis. Thus, the cerebellum acts as one important node in the working memory circuit, and when the cerebellum is involved in childhood disorders, deficits in working memory commonly occur.

Goal-Directed-Behavior in 22q11.2 Deletion Syndrome: Implication for Social Dysfunctions and the Emergence of Negative Symptoms

BACKGROUND

Negative symptoms and social dysfunction are core features of the 22q11.2 deletion syndrome (22q11DS). Negative symptoms have been conceptualized as pathology of goal-directed-behaviors. Moreover, goal-directed-behaviors also appear to be a crucial step of social interactions. However, in 22q11DS, the extent to which goal-directed-behavior could be linked to social functioning difficulties and negative symptoms has never been examined.

METHOD

Verbal and nonverbal initiation was measured using the verbal fluency and figural fluency tasks in 93 individuals with 22q11DS and 57 healthy controls aged between 8 and 30 years in order to assess goal-directed-behavior ability. The associations between initiation scores and social functioning/negative symptoms were investigated. In addition, the effect of COMT Val/Met polymorphism on initiation competences was examined.

RESULTS

Results revealed diminished verbal and nonverbal initiation ability in 22q11DS individuals compared to controls. A positive correlation between verbal initiation and social functioning was found as well as between verbal initiation and negative symptoms, in particular social anhedonia. No differences in terms of initiation scores were found between individuals with 22q11DS carrying Met and Val polymorphism.

CONCLUSION

Results indicate impaired goal-directed-behavior in the 22q11DS population. These deficits seem to support social functioning impairments frequently observed in the 22q11DS and to a lesser extent the expression of negative symptoms.

Regions of white matter abnormalities in the arcuate fasciculus in veterans with anger and aggression problems

Aggression after military deployment is a common occurrence in veterans. Neurobiological research has shown that aggression is associated with a dysfunction in a network connecting brain regions implicated in threat processing and emotion regulation. However, aggression may also be related to deficits in networks underlying communication and social cognition. The uncinate and arcuate fasciculi are integral to these networks, thus studying potential abnormalities in these white matter connections can further our understanding of anger and aggression problems in military veterans. Here, we use diffusion tensor imaging tractography to investigate white matter microstructural properties of the uncinate fasciculus and the arcuate fasciculus in veterans with and without anger and aggression problems. A control tract, the parahippocampal cingulum was also included in the analyses. More specifically, fractional anisotropy (FA) estimates are derived along the trajectory from all fiber pathways and compared between both groups. No between-group FA differences are observed for the uncinate fasciculus and the cingulum, however parts of the arcuate fasciculus show a significantly lower FA in the group of veterans with aggression and anger problems. Our data suggest that abnormalities in arcuate fasciculus white matter connectivity that are related to self-regulation may play an important role in the etiology of anger and aggression in military veterans.

Development of Structural Covariance From Childhood to Adolescence: A Longitudinal Study in 22q11.2DS

Background: Schizophrenia is currently considered a neurodevelopmental disorder of connectivity. Still few studies have investigated how brain networks develop in children and adolescents who are at risk for developing psychosis. 22q11.2 Deletion Syndrome (22q11DS) offers a unique opportunity to investigate the pathogenesis of schizophrenia from a neurodevelopmental perspective. Structural covariance (SC) is a powerful approach to explore morphometric relations between brain regions that can furthermore detect biomarkers of psychosis, both in 22q11DS and in the general population.

Methods: Here we implement a state-of-the-art sliding-window approach to characterize maturation of SC network architecture in a large longitudinal cohort of patients with 22q11DS (110 with 221 visits) and healthy controls (117 with 211 visits). We furthermore propose a new clustering-based approach to group regions according to trajectories of structural connectivity maturation. We correlate measures of SC with development of working memory, a core executive function that is highly affected in both idiopathic psychosis and 22q11DS. Finally, in 22q11DS we explore correlations between SC dysconnectivity and severity of internalizing psychopathology.

Results: In HCs network architecture underwent a quadratic developmental trajectory maturing up to mid-adolescence. Late-childhood maturation was particularly evident for fronto-parietal cortices, while Default-Mode-Network-related regions showed a more protracted linear development. Working memory performance was positively correlated with network segregation and fronto-parietal connectivity. In 22q11DS, we demonstrate aberrant maturation of SC with disturbed architecture selectively emerging during adolescence and correlating more severe internalizing psychopathology. Patients also presented a lack of typical network development during late-childhood, that was particularly prominent for frontal connectivity.

Conclusions: Our results suggest that SC maturation may underlie critical cognitive development occurring during late-childhood in healthy controls. Aberrant trajectories of SC maturation may reflect core developmental features of 22q11DS, including disturbed cognitive maturation during childhood and predisposition to internalizing psychopathology and psychosis during adolescence.

Genomic and Imaging Biomarkers in Schizophrenia

Recent large-scale genomic studies have confirmed that schizophrenia is a polygenic syndrome and have implicated a number of biological pathways in its aetiology. Both common variants individually of small effect and rarer but more penetrant genetic variants have been shown to play a role in the pathogenesis of the disorder. No simple Mendelian forms of the condition have been identified, but progress has been made in stratifying risk on the basis of the polygenic burden of common variants individually of small effect, and the contribution of rarer variants of larger effect such as Copy Number Variants (CNVs). Pathway analysis of risk-associated variants has begun to identify specific biological processes implicated in risk for the disorder, including elements of the glutamatergic NMDA receptor complex and post synaptic density, voltage-gated calcium channels, targets of the Fragile X Mental Retardation Protein (FMRP targets) and immune pathways. Genetic studies have also been used to drive genomic imaging approaches to the investigation of brain markers associated with risk for the disorder. Genomic imaging approaches have been applied both to investigate the effect of polygenic risk and to study the impact of individual higher-penetrance variants such as CNVs. Both genomic and genomic imaging approaches offer potential for the stratification of patients and at-risk groups and the development of better biomarkers of risk and treatment response; however, further research is needed to integrate this work and realise the full potential of these approaches.

Working Memory Impairments in Chromosome 22q11.2 Deletion Syndrome: The Roles of Anxiety and Stress Physiology

Stress and anxiety have a negative impact on working memory systems by competing for executive resources and attention. Broad memory deficits, anxiety, and elevated stress have been reported in individuals with chromosome 22q11.2 deletion syndrome (22q11.2DS). We investigated anxiety and physiological stress reactivity in relation to visuospatial working memory impairments in 20 children with 22q11.2DS and 32 typically developing (TD) children ages 7 to 16. Children with 22q11.2DS demonstrated poorer working memory, reduced post-stress respiratory sinus arrhythmia recovery, and overall increased levels of cortisol in comparison to TD children. Anxiety, but not physiological stress responsivity, mediated the relationship between 22q11.2DS diagnosis and visuospatial working memory impairment. Findings indicate that anxiety exacerbates impaired working memory in children with 22q11.2DS.

Haploinsufficiency of the 22q11.2 microdeletion gene Mrpl40 disrupts short-term synaptic plasticity and working memory through dysregulation of mitochondrial calcium

Hemizygous deletion of a 1.5- to 3-megabase region on chromosome 22 causes 22q11.2 deletion syndrome (22q11DS), which constitutes one of the strongest genetic risks for schizophrenia. Mouse models of 22q11DS have abnormal short-term synaptic plasticity that contributes to working-memory deficiencies similar to those in schizophrenia. We screened mutant mice carrying hemizygous deletions of 22q11DS genes and identified haploinsufficiency of Mrpl40 (mitochondrial large ribosomal subunit protein 40) as a contributor to abnormal short-term potentiation (STP), a major form of short-term synaptic plasticity. Two-photon imaging of the genetically encoded fluorescent calcium indicator GCaMP6, expressed in presynaptic cytosol or mitochondria, showed that Mrpl40 haploinsufficiency deregulates STP via impaired calcium extrusion from the mitochondrial matrix through the mitochondrial permeability transition pore. This led to abnormally high cytosolic calcium transients in presynaptic terminals and deficient working memory but did not affect long-term spatial memory. Thus, we propose that mitochondrial calcium deregulation is a novel pathogenic mechanism of cognitive deficiencies in schizophrenia.

Frontal Hypoactivation During a Working Memory Task in Children With 22q11 Deletion Syndrome

Impairments in executive function, such as working memory, are almost universal in children with chromosome 22q11.2 deletion syndrome. Delineating the neural underpinnings of these functions would enhance understanding of these impairments. In this study, children and adolescents with 22q11 deletion syndrome were compared with healthy control participants in a functional magnetic resonance imaging (MRI) study of working memory. When the 2-back condition was contrasted with the 1-back and 0-back conditions, the participants with 22q11 deletion syndrome showed lower activation in several brain areas involved in working memory-notably dorsolateral prefrontal cortex, anterior cingulate, and precuneus. This hypoactivation may be due to reduced gray matter volumes or white matter connectivity in the frontal and parietal regions, differences that have previously been documented in children with 22q11 deletion syndrome. Understanding differences in brain function will provide a foundation for future interventions to address the wide range of neurodevelopmental deficits observed in 22q11 deletion syndrome.

Potential Role of Cortisol in Social and Memory Impairments in Individuals with 22q11.2 Deletion Syndrome

22q11.2 Deletion syndrome is a genetic disorder characterized by physiological and psychological symptoms. This study investigated the role of cortisol on the social and cognitive impairments in children with 22q11.2. A total of 11 children with 22q11.2 were assessed for baseline cortisol levels and received broad neuropsychological testing. Results were compared with 11 controls. Children with 22q11.2 had significantly higher cortisol levels. A significant negative correlation was observed between the general memory and attention/concentration indices of the Wide Range Assessment of Memory and Learning, 2nd edition and cortisol concentrations in the control population. These data provide evidence of a possible causal mechanism that underlies social impairments in stress disorders.

Altered Brain Structure-Function Relationships Underlie Executive Dysfunction in 22q11.2 Deletion Syndrome

22q11.2 deletion syndrome (22q11DS) is a neurogenetic disorder associated with elevated rates of developmental neuropsychiatric disorders and impaired executive function (EF). Disrupted brain structure-function relationships may underlie EF deficits in 22q11DS. We administered the Behavior Rating Inventory of Executive Function (BRIEF) to assess real-world EF in patients with 22q11DS and matched controls (n = 86; age 6-17 years), along with cognitive measures that tap behavioral regulation and metacognition aspects of EF. Using FreeSurfer's whole-brain vertex cortical thickness pipeline, we investigated brain structure-EF relationships in patients with 22q11DS and controls. Behaviorally, patients with 22q11DS were impaired on multiple EF measures. Right orbitofrontal cortical thickness showed a differential relationship between real-world EF in patients with 22q11DS and controls. We also observed a group difference in the relationship between behavioral regulation and metacognition measures with thickness of ventral and dorsolateral prefrontal regions, respectively. Our findings suggest that executive dysfunction characteristic of 22q11DS is underscored by altered prefrontal cortical structure.

Modeling a model: Mouse genetics, 22q11.2 Deletion Syndrome, and disorders of cortical circuit development

Understanding the developmental etiology of autistic spectrum disorders, attention deficit/hyperactivity disorder and schizophrenia remains a major challenge for establishing new diagnostic and therapeutic approaches to these common, difficult-to-treat diseases that compromise neural circuits in the cerebral cortex. One aspect of this challenge is the breadth and overlap of ASD, ADHD, and SCZ deficits; another is the complexity of mutations associated with each, and a third is the difficulty of analyzing disrupted development in at-risk or affected human fetuses. The identification of distinct genetic syndromes that include behavioral deficits similar to those in ASD, ADHC and SCZ provides a critical starting point for meeting this challenge. We summarize clinical and behavioral impairments in children and adults with one such genetic syndrome, the 22q11.2 Deletion Syndrome, routinely called 22q11DS, caused by micro-deletions of between 1.5 and 3.0 MB on human chromosome 22. Among many syndromic features, including cardiovascular and craniofacial anomalies, 22q11DS patients have a high incidence of brain structural, functional, and behavioral deficits that reflect cerebral cortical dysfunction and fall within the spectrum that defines ASD, ADHD, and SCZ. We show that developmental pathogenesis underlying this apparent genetic "model" syndrome in patients can be defined and analyzed mechanistically using genomically accurate mouse models of the deletion that causes 22q11DS. We conclude that "modeling a model", in this case 22q11DS as a model for idiopathic ASD, ADHD and SCZ, as well as other behavioral disorders like anxiety frequently seen in 22q11DS patients, in genetically engineered mice provides a foundation for understanding the causes and improving diagnosis and therapy for these disorders of cortical circuit development.

White matter microstructural abnormalities of the cingulum bundle in youths with 22q11.2 deletion syndrome: associations with medication, neuropsychological function, and prodromal symptoms of psychosis

BACKGROUND

The 22q11.2 deletion syndrome (22q11.2DS) is regarded as an etiologically homogenous model for understanding neuroanatomic disruptions associated with a high risk for schizophrenia. This study utilized diffusion tensor imaging (DTI) to analyze white matter microstructure in individuals with 22q11.2DS. We focused on the cingulum bundle (CB), previously shown to be disrupted in patients with schizophrenia and associated with symptoms of psychosis.

METHODS

White matter microstructure was assessed in the anterior, superior, and posterior CB using the tractography algorithm in DTIStudio. Neuropsychological function, presence of prodromal symptoms of psychosis, and medication history were assessed in all participants.

RESULTS

Relative to controls, young adults with 22q11.2DS showed alterations in most DTI metrics of the CB. Alterations were associated with positive prodromal symptoms of psychosis. However, when individuals with 22q11.2DS were divided by usage of antipsychotics/mood stabilizers, the medicated and non-medicated groups differed significantly in axial diffusivity of the anterior CB and in fractional anisotropy of the superior CB. DTI metrics did not differ between the medicated group and the control group.

CONCLUSIONS

Results suggest that the microstructure of the CB is altered in individuals with 22q11.2DS, and that those alterations may underlie positive prodromal symptoms of psychosis. Our findings further provide preliminary evidence that antipsychotic/mood stabilizer usage may have a reparative effect on white matter microstructure in prodromal 22q11.2DS, independent of the potential effects of psychosis. Future studies of white matter pathology in individuals with 22q11.2DS should test for potential effects of medication on white matter microstructure.

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.

Children with chromosome 22q11.2 deletion syndrome exhibit impaired spatial working memory

Individuals with chromosome 22q11.2 deletion syndrome (22q11.2DS) have been shown to have impairments in processing spatiotemporal information. The authors examined whether children with 22q11.2DS exhibit impairments in spatial working memory performance due to these weaknesses, even when controlling for maintenance of attention. Children with 22q11.2DS (n  =  47) and typically developing controls (n  =  49) ages 6-15 years saw images within a grid and after a delay, then indicated the positions of the images in the correct temporal order. Children with 22q11.2DS made more spatial and temporal errors than controls. Females with 22q11.2DS made more spatial and temporal errors than males. These results extend findings of impaired spatiotemporal processing into the memory domain in 22q11.2DS by documenting their influence on working memory performance.

Disrupted working memory circuitry and psychotic symptoms in 22q11.2 deletion syndrome

22q11.2 deletion syndrome (22q11DS) is a recurrent genetic mutation that is highly penetrant for psychosis. Behavioral research suggests that 22q11DS patients exhibit a characteristic neurocognitive phenotype that includes differential impairment in spatial working memory (WM). Notably, spatial WM has also been proposed as an endophenotype for idiopathic psychotic disorder, yet little is known about the neurobiological substrates of WM in 22q11DS. In order to investigate the neural systems engaged during spatial WM in 22q11DS patients, we collected functional magnetic resonance imaging (fMRI) data while 41 participants (16 22q11DS patients, 25 demographically matched controls) performed a spatial capacity WM task that included manipulations of delay length and load level. Relative to controls, 22q11DS patients showed reduced neural activation during task performance in the intraparietal sulcus (IPS) and superior frontal sulcus (SFS). In addition, the typical increases in neural activity within spatial WM-relevant regions with greater memory load were not observed in 22q11DS. We further investigated whether neural dysfunction during WM was associated with behavioral WM performance, assessed via the University of Maryland letter-number sequencing (LNS) task, and positive psychotic symptoms, assessed via the Structured Interview for Prodromal Syndromes (SIPS), in 22q11DS patients. WM load activity within IPS and SFS was positively correlated with LNS task performance; moreover, WM load activity within IPS was inversely correlated with the severity of unusual thought content and delusional ideas, indicating that decreased recruitment of working memory-associated neural circuitry is associated with more severe positive symptoms. These results suggest that 22q11DS patients show reduced neural recruitment of brain regions critical for spatial WM function, which may be related to characteristic behavioral manifestations of the disorder.

White matter abnormalities in 22q11.2 deletion syndrome: preliminary associations with the Nogo-66 receptor gene and symptoms of psychosis

BACKGROUND

This study utilized diffusion tensor imaging (DTI) to analyze white matter tractography in the anterior limb of the internal capsule (ALIC), fornix, and uncinate fasciculus (UF) of individuals with 22q11.2 deletion syndrome and controls. Aberrations in these tracts have been previously associated with schizophrenia. With up to 25% of individuals with 22q11.2DS developing schizophrenia in adulthood, we hypothesized reduction in structural integrity of these tracts, including an association with prodromal symptoms of psychosis. We further predicted an association between allelic variation in a functional polymorphism of the Nogo-66 receptor gene and 22q11.2DS white matter integrity.

METHODS

Tractography was conducted using fiber assignment by streamline tracking algorithm in DTI Studio. Subjects were genotyped for the rs701428 SNP of the Nogo-66 receptor gene, and assessed for presence of prodromal symptoms.

RESULTS

We found significant group differences between 22q11.2DS and controls in DTI metrics for all three tracts. DTI metrics of ALIC and UF were associated with prodromal symptoms in 22q11.2DS. Further, ALIC DTI metrics were associated with allelic variation of the rs701428 SNP of the Nogo-66 receptor gene in 22q11.2DS.

CONCLUSIONS

Alterations in DTI metrics suggest white matter microstructural anomalies of the ALIC, fornix, and UF in 22q11.2DS. Structural differences in ALIC appear to be associated with the Nogo-66 receptor gene, which has been linked to myelin-mediated axonal growth inhibition. Moreover, the association between psychosis symptoms and ALIC and UF metrics suggests that the Nogo-66 receptor gene may represent a susceptibility gene for psychosis through its disruption of white matter microstructure and myelin-associated axonal growth.

The pattern of cortical dysfunction in a mouse model of a schizophrenia-related microdeletion

We used a mouse model of the schizophrenia-predisposing 22q11.2 microdeletion to evaluate how this genetic lesion affects cortical neural circuits at the synaptic, cellular, and molecular levels. Guided by cognitive deficits, we demonstrated that mutant mice display robust deficits in high-frequency synaptic transmission and short-term plasticity (synaptic depression and potentiation), as well as alterations in long-term plasticity and dendritic spine stability. Apart from previously reported reduction in dendritic complexity of layer 5 pyramidal neurons, altered synaptic plasticity occurs in the context of relatively circumscribed and often subtle cytoarchitectural changes in neuronal density and inhibitory neuron numbers. We confirmed the pronounced DiGeorge critical region 8 (Dgcr8)-dependent deficits in primary micro-RNA processing and identified additional changes in gene expression and RNA splicing that may underlie the effects of this mutation. Reduction in Dgcr8 levels appears to be a major driver of altered short-term synaptic plasticity in prefrontal cortex and working memory but not of long-term plasticity and cytoarchitecture. Our findings inform the cortical synaptic and neuronal mechanisms of working memory impairment in the context of psychiatric disorders. They also provide insight into the link between micro-RNA dysregulation and genetic liability to schizophrenia and cognitive dysfunction.

Understanding velocardiofacial syndrome: how recent discoveries can help you improve your patient outcomes

PURPOSE OF REVIEW

Improved recognition of velocardiofacial syndrome (VCFS) has led to increasing awareness of VCFS by otolaryngologists. Understanding the developmental biologic processes affected in VCFS patients will help improve treatment and outcomes. Advanced application of molecular labeling techniques has better outlined the role of T-Box transcription factor 1 (TBX1) as the primary genetic anomaly leading to VCFS. TBX1 plays multiple roles during branchial, cardiac, and craniofacial development and increased understanding of how these systems are affected by TBX1 mutations will improve patient outcomes. Furthermore, additional modifiers of TBX1 expression have been identified that may explain the variability of VCFS phenotypes. The phenotypic spectrum of VCFS may include cardiac anomalies, velopharyngeal insufficiency, aberrant calcium metabolism, and immune dysfunction. Recent interest has focused on the cognitive and neuropsychiatric manifestations of VCFS. Improved understanding of the biology of VCFS associated mutations has the potential to improve therapeutic outcomes.

RECENT FINDINGS

This article will discuss recent developmental biologic understanding of the role of TBX1 and genetic modifiers generating the phenotypic variability seen in VCFS patients. Special attention is given to advances in the realms of immunodeficiency, hypocalcemia, cardiac and arterial patterning anomalies, velopharyngeal insufficiency, as well as cognitive and psychiatric problems.

SUMMARY

Enhanced understanding of the multiple systems affected by TBX1 mutations will result in improved patient outcomes and improved family education. Future research will lead to improved detection of potential targets for gene therapy and change the way physicians counsel families and treat patients.

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.

Atlas-based white matter analysis in individuals with velo-cardio-facial syndrome (22q11.2 deletion syndrome) and unaffected siblings

Background

Velo-cardio-facial syndrome (VCFS, MIM#192430, 22q11.2 Deletion Syndrome) is a genetic disorder caused by a deletion of about 40 genes at the q11.2 band of one copy of chromosome 22. Individuals with VCFS present with deficits in cognition and social functioning, high risk of psychiatric disorders, volumetric reductions in gray and white matter (WM) and some alterations of the WM microstructure. The goal of the current study was to characterize the WM microstructural differences in individuals with VCFS and unaffected siblings, and the correlation of WM microstructure with neuropsychological performance. We hypothesized that individuals with VCFS would have decreased indices of WM microstructure (fractional anisotropy (FA), axial diffusivity (AD) and radial diffusivity (RD)), particularly in WM tracts to the frontal lobe, and that these measures would be correlated with cognitive functioning.

Methods

Thirty-three individuals with VCFS (21 female) and 16 unaffected siblings (8 female) participated in DTI scanning and neuropsychological testing. We performed an atlas-based analysis, extracted FA, AD, and RD measures for 54 WM tracts (27 in each hemisphere) for each participant, and used MANOVAs to compare individuals with VCFS to siblings. For WM tracts that were statistically significantly different between VCFS and siblings (p_FDR < 0.05), we assessed the correlations between DTI and neuropsychological measures.

Results

In VCFS individuals as compared to unaffected siblings, we found decreased FA in the uncinate fasciculus, and decreased AD in multiple WM tracts (bilateral superior and posterior corona radiata, dorsal cingulum, inferior fronto-occipital fasciculus, superior longitudinal fasciculus, superior cerebellar peduncle, posterior thalamic radiation, and left anterior corona radiata, retrolenticular part of the internal capsule, external capsule, sagittal stratum). We also found significant correlations of AD with measures of executive function, IQ, working memory, and/or social cognition.

Conclusions

Our results suggest that individuals with VCFS display abnormal WM connectivity in a widespread cerebro-anatomical network, involving tracts from/to all cerebral lobes and the cerebellum. Future studies could focus on the WM developmental trajectory in VCFS, the association of WM alterations with psychiatric disorders, and the effects of candidate 22q11.2 genes on WM anomalies.

Phenotypic regional functional imaging patterns during memory encoding in mild cognitive impairment and Alzheimer's disease

BACKGROUND

Reliable blood-oxygen-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) phenotypic biomarkers of Alzheimer's disease (AD) or mild cognitive impairment (MCI) are likely to emerge only from a systematic, quantitative, and aggregate examination of the functional neuroimaging research literature.

METHODS

A series of random-effects activation likelihood estimation (ALE) meta-analyses were conducted on studies of episodic memory encoding operations in AD and MCI samples relative to normal controls. ALE analyses were based on a thorough literature search for all task-based functional neuroimaging studies in AD and MCI published up to January 2010. Analyses covered 16 fMRI studies, which yielded 144 distinct foci for ALE meta-analysis.

RESULTS

ALE results indicated several regional task-based BOLD consistencies in MCI and AD patients relative to normal control subjects across the aggregate BOLD functional neuroimaging research literature. Patients with AD and those at significant risk (MCI) showed statistically significant consistent activation differences during episodic memory encoding in the medial temporal lobe, specifically parahippocampal gyrus, as well superior frontal gyrus, precuneus, and cuneus, relative to normal control subjects.

CONCLUSIONS

ALE consistencies broadly support the presence of frontal compensatory activity, medial temporal lobe activity alteration, and posterior midline "default mode" hyperactivation during episodic memory encoding attempts in the diseased or prospective predisease condition. Taken together, these robust commonalities may form the foundation for a task-based fMRI phenotype of memory encoding in AD.

Comprehensive neurocognitive endophenotyping strategies for mouse models of genetic disorders

There is a need for refinement of the current behavioral phenotyping methods for mouse models of genetic disorders. The current approach is to perform a behavioral screen using standardized tasks to define a broad phenotype of the model. This phenotype is then compared to what is known concerning the disorder being modeled. The weakness inherent in this approach is twofold: First, the tasks that make up these standard behavioral screens do not model specific behaviors associated with a given genetic mutation but rather phenotypes affected in various genetic disorders; secondly, these behavioral tasks are insufficiently sensitive to identify subtle phenotypes. An alternate phenotyping strategy is to determine the core behavioral phenotypes of the genetic disorder being studied and develop behavioral tasks to evaluate specific hypotheses concerning the behavioral consequences of the genetic mutation. This approach emphasizes direct comparisons between the mouse and human that facilitate the development of neurobehavioral biomarkers or quantitative outcome measures for studies of genetic disorders across species.

Comparing the neural bases of self-referential processing in typically developing and 22q11.2 adolescents

The investigation of self-reflective processing during adolescence is relevant, as this period is characterized by deep reorganization of the self-concept. It may be the case that an atypical development of brain regions underlying self-reflective processing increases the risk for psychological disorders and impaired social functioning. In this study, we investigated the neural bases of self- and other-related processing in typically developing adolescents and youths with 22q11.2 deletion syndrome (22q11DS), a rare neurogenetic condition associated with difficulties in social interactions and increased risk for schizophrenia. The fMRI paradigm consisted in judging if a series of adjectives applied to the participant himself/herself (self), to his/her best friend or to a fictional character (Harry Potter). In control adolescents, we observed that self- and other-related processing elicited strong activation in cortical midline structures (CMS) when contrasted with a semantic baseline condition. 22q11DS exhibited hypoactivation in the CMS and the striatum during the processing of self-related information when compared to the control group. Finally, the hypoactivation in the anterior cingulate cortex was associated with the severity of prodromal positive symptoms of schizophrenia. The findings are discussed in a developmental framework and in light of their implication for the development of schizophrenia in this at-risk population.

Computerized neurocognitive profile in young people with 22q11.2 deletion syndrome compared to youths with schizophrenia and at-risk for psychosis

Adults with 22q11.2 Deletion syndrome (22q11DS) have increased prevalence of schizophrenia features. Our goal is to compare the neurocognitive profile in 22q11DS, schizophrenia and individuals at risk for schizophrenia. Twenty-one 22q11DS patients (8-32 years, mean 14.9 years, 15M, 6F) were matched to four comparison groups on age: low risk (n = 21), first-degree family members of schizophrenia patients (genetic risk, n = 20), individuals exhibiting putatively prodromal symptoms (clinical risk, n = 19), and patients with schizophrenia (n = 21). All participants received semi-structured interviews [Diagnostic Interview for Genetic Studies (DIGS) and the Structured Interview for Prodromal Syndromes (SIPS)], and a computerized neurocognitive battery (CNB) measuring the following domains: Abstraction and Mental Flexibility, Attention, Working Memory, Verbal Memory, Face Memory, Spatial Memory, Language, Spatial Processing, Sensorimotor Dexterity, and Emotion Processing. Sixty percent of 22q11DS participants met SIPS criteria for prodromal symptoms and one participant met criteria for paranoid schizophrenia. Thirty-eight percent met criteria for Depressive Disorders. All 22q11DS participants successfully completed the CNB. 22q11DS participants were significantly less accurate in nearly all domains, but had similar speed of response compared to the other groups. Their profile resembled that of the psychosis groups in accuracy and speed, except for more pronounced deficits in accuracy for face memory and emotion processing. Subthreshold psychotic symptoms are present in a high proportion of 22q11DS participants. Deficits shown in the CNB are more pronounced for accuracy than speed relative to the psychosis groups with similar profiles. Similar deficits have been described in the 22q11DS population using non-computerized measures, which require increased testing time.

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.

The 22q11.2 microdeletion: fifteen years of insights into the genetic and neural complexity of psychiatric disorders

Over the last fifteen years it has become established that 22q11.2 deletion syndrome (22q11DS) is a true genetic risk factor for schizophrenia. Carriers of deletions in chromosome 22q11.2 develop schizophrenia at rate of 25-30% and such deletions account for as many as 1-2% of cases of sporadic schizophrenia in the general population. Access to a relatively homogeneous population of individuals that suffer from schizophrenia as the result of a shared etiological factor and the potential to generate etiologically valid mouse models provides an immense opportunity to better understand the pathobiology of this disease. In this review we survey the clinical literature associated with the 22q11.2 microdeletions with a focus on neuroanatomical changes. Then, we highlight results from work modeling this structural mutation in animals. The key biological pathways disrupted by the mutation are discussed and how these changes impact the structure and function of neural circuits is described.

Mapping cortical morphology in youth with velocardiofacial (22q11.2 deletion) syndrome

OBJECTIVE

Velocardiofacial syndrome (VCFS; 22q11.2 deletion syndrome) represents one of the highest known risk factors for schizophrenia. Insofar as up to 30% of individuals with this genetic disorder develop schizophrenia, VCFS constitutes a unique, etiologically homogeneous model for understanding the pathogenesis of schizophrenia.

METHOD

Using a longitudinal, case-control design, anatomic magnetic resonance images were acquired to investigate cross-sectional and longitudinal alterations in surface cortical morphology in a cohort of adolescents with VCFS and age-matched typical controls. All participants were scanned at two time points.

RESULTS

Compared with controls, youth with VCFS exhibited alterations in inferior frontal, dorsal frontal, occipital, and cerebellar brain regions at both time points. Little change was observed over time in surface morphology of either study group. However, within the VCFS group only, worsening psychosocial functioning over time was associated with time 2 surface contractions in left middle and inferior temporal gyri. Further, prodromal symptoms at time 2 were associated with surface contractions in the left and right orbitofrontal, temporal, and cerebellar regions and surface protrusions of the supramarginal gyrus.

CONCLUSIONS

These findings advance the understanding of cortical disturbances in VCFS that produce vulnerability for psychosis in this high-risk population.

Deficiency of Dgcr8, a gene disrupted by the 22q11.2 microdeletion, results in altered short-term plasticity in the prefrontal cortex

Individuals with 22q11.2 microdeletions have cognitive and behavioral impairments and the highest known genetic risk for developing schizophrenia. One gene disrupted by the 22q11.2 microdeletion is DGCR8, a component of the "microprocessor" complex that is essential for microRNA production, resulting in abnormal processing of specific brain miRNAs and working memory deficits. Here, we determine the effect of Dgcr8 deficiency on the structure and function of cortical circuits by assessing their laminar organization, as well as the neuronal morphology, and intrinsic and synaptic properties of layer 5 pyramidal neurons in the prefrontal cortex of Dgcr8(+/-) mutant mice. We found that heterozygous Dgcr8 mutant mice have slightly fewer cortical layer 2/4 neurons and that the basal dendrites of layer 5 pyramidal neurons have slightly smaller spines. In addition to the modest structural changes, field potential and whole-cell electrophysiological recordings performed in layer 5 of the prefrontal cortex revealed greater short-term synaptic depression during brief stimulation trains applied at 50 Hz to superficial cortical layers. This finding was accompanied by a decrease in the initial phase of synaptic potentiation. Our results identify altered short-term plasticity as a neural substrate underlying the cognitive dysfunction and the increased risk for schizophrenia associated with the 22q11.2 microdeletions.

Chromosome 22q11.2 deletion syndrome (DiGeorge syndrome/velocardiofacial syndrome)

Chromosome 22q11.2 deletion syndrome is a common syndrome also known as DiGeorge syndrome and velocardiofacial syndrome. It occurs in approximately 1:4000 births, and the incidence is increasing due to affected parents bearing their own affected children. The manifestations of this syndrome cross all medical specialties, and care of the children and adults can be complex. Many patients have a mild to moderate immune deficiency, and the majority of patients have a cardiac anomaly. Additional features include renal anomalies, eye anomalies, hypoparathyroidism, skeletal defects, and developmental delay. Each child's needs must be tailored to his or her specific medical problems, and as the child transitions to adulthood, additional issues will arise. A holistic approach, addressing medical and behavioral needs, can be very helpful.

Atypical development of the executive attention network in children with chromosome 22q11.2 deletion syndrome

Impairment in the executive control of attention has been found in youth with chromosome 22q11.2 deletion syndrome (22q11.2DS). However, how this impairment is modified by other factors, particularly age, is unknown. Forty-six typically developing and 53 children with 22q11.2DS were tested with the attention networks task (ANT) in this cross-sectional study. We used logarithmic transform and linear modeling to assess age effects on the executive index of the ANT. Mixed modeling accounted for between subject variability, age, handedness, catecholamine-O-transferase (COMT; codon 158) genotype, and gender on performance for all experimental conditions (cue × flanker) and their two-level interactions. Children with 22q11.2DS showed a relative, age-dependent executive index impairment but not orienting or alerting network index impairments. In factorial analysis, age was a major predictor of overall performance. There was a significant effect of the 22q11.2DS on overall performance. Of note, children with 22q11.2DS are specifically vulnerable to incongruent flanker interference, especially at younger ages. We did not find an overall effect of COMT genotype or handedness. Children with 22q11.2DS demonstrated age-related impairment in the executive control of attention. Future investigation will likely reveal that there are different developmental trajectories of executive attentional function likely related to the development of schizophrenia in 22q11.2DS.

How might stress contribute to increased risk for schizophrenia in children with chromosome 22q11.2 deletion syndrome?

The most common human microdeletion occurs at chromosome 22q11.2. The associated syndrome (22q11.2DS) has a complex and variable phenotype with a high risk of schizophrenia. While the role of stress in the etiopathology of schizophrenia has been under investigation for over 30 years (Walker et al. 2008), the stress–diathesis model has yet to be investigated in children with 22q11.2DS. Children with 22q11.2DS face serious medical, behavioral, and socioemotional challenges from infancy into adulthood. Chronic stress elevates glucocorticoids, decreases immunocompetence, negatively impacts brain development and function, and is associated with psychiatric illness in adulthood. Drawing knowledge from the extant and well-developed anxiety and stress literature will provide invaluable insight into the complex etiopathology of schizophrenia in people with 22q11.2DS while suggesting possible early interventions. Childhood anxiety is treatable and stress coping skills can be developed thereby improving quality of life in the short-term and potentially mitigating the risk of developing psychosis.

Striatal D₂ receptor binding in 22q11 deletion syndrome: an [¹²³I]IBZM SPECT study

It has been hypothesised that in subjects with 22q11 deletion syndrome (22q11DS) disturbances of the dopamine (DA) system contribute to their increased risk for cognitive deficits and psychiatric problems. However, central DAergic neurotransmission in 22q11DS has not been investigated. We measured striatal D₂ receptor binding potential (D₂R BP(ND)) using (S)-(-)-3-iodo-2-hydroxy-6-methoxy-N-[(1-ethyl-2-pyrrolidinyl)methyl] benzamide-single photon emission computed tomography ([¹²³I]IBZM SPECT) in 12 adults with 22q11DS and 12 matched controls. Correlations between D₂R BP(ND) and plasma prolactin (pPRL) levels were also determined. 22q11DS subjects and controls had similar D₂R BP( ND). There was a positive correlation between D₂R BP( ND) and pPRL values in controls, but no such relation was found in 22q11DS subjects. This study suggests that a 22q11 deletion does not affect striatal DAergic neurotransmission in the living human brain. However, the disturbed relationship between D₂R BP(ND) and pPRL values suggests DAergic dysfunction at a different level. Further studies on DAergic function in extra-striatal brain regions and under challenged conditions are needed.

Reduced NoGo-anteriorisation during continuous performance test in deletion syndrome 22q11.2

Deletion syndrome 22q11.2 (DS22q11.2) is a high-risk factor for psychiatric disorders. Alterations in brain morphology and function including the anterior cingulate cortex (ACC) are suggested to underlie the increased psychiatric disposition. We assessed response-inhibition in patients with DS22q11.2 (n=13) and healthy controls (n=13) matched for age, sex, and handedness by means of a Go-NoGo-Task during recording of a multi-channel electroencephalography (EEG). Analysis of event-related potentials (P300) resulted in an aberrant topographical pattern and NoGo-anteriorisation (NGA) as a parameter of medial prefrontal function was significantly reduced in patients with DS22q11.2 compared to controls. Differences in IQ between groups did not account for the findings. Source localization analysis (LORETA) revealed diminished left temporal brain activation during the Go-condition, but no altered ACC activation in DS22q11 during the NoGo-condition. Despite recent reports of structural alterations of the ACC in DS22q11.2 our findings suggest that response-inhibition mediated by the ACC is not impaired in DS22q11.2.

MicroRNAs in psychiatric and neurodevelopmental disorders

Abnormalities in microRNA (miRNA)-mediated gene regulation have been observed in a variety of human diseases, especially in cancer. Here, we provide an account of newly emerging connections between miRNAs with various psychiatric and neurodevelopmental disorders, including recent findings of miRNA dysregulation in the 22q11.2 microdeletion syndrome, a well-established genetic risk factor for schizophrenia. miRNAs appear to be components of both the genetic architecture of these complex phenotypes as well as integral parts of the biological pathways that mediate the effects of primary genetic deficits. Therefore, they may contribute to both genetic heterogeneity and phenotypic variation of psychiatric and neurodevelopmental disorders and could serve as novel therapeutic targets.

22q11.2 microdeletions: linking DNA structural variation to brain dysfunction and schizophrenia

Recent studies are beginning to paint a clear and consistent picture of the impairments in psychological and cognitive competencies that are associated with microdeletions in chromosome 22q11.2. These studies have highlighted a strong link between this genetic lesion and schizophrenia. Parallel studies in humans and animal models are starting to uncover the complex genetic and neural substrates altered by the microdeletion. In addition to offering a deeper understanding of the effects of this genetic lesion, these findings may guide analysis of other copy-number variants associated with cognitive dysfunction and psychiatric disorders.

Impaired hippocampal-prefrontal synchrony in a genetic mouse model of schizophrenia

Abnormalities in functional connectivity between brain areas have been postulated as an important pathophysiological mechanism underlying schizophrenia. In particular, macroscopic measurements of brain activity in patients suggest that functional connectivity between the frontal and temporal lobes may be altered. However, it remains unclear whether such dysconnectivity relates to the aetiology of the illness, and how it is manifested in the activity of neural circuits. Because schizophrenia has a strong genetic component, animal models of genetic risk factors are likely to aid our understanding of the pathogenesis and pathophysiology of the disease. Here we study Df(16)A(+/-) mice, which model a microdeletion on human chromosome 22 (22q11.2) that constitutes one of the largest known genetic risk factors for schizophrenia. To examine functional connectivity in these mice, we measured the synchronization of neural activity between the hippocampus and the prefrontal cortex during the performance of a task requiring working memory, which is one of the cognitive functions disrupted in the disease. In wild-type mice, hippocampal-prefrontal synchrony increased during working memory performance, consistent with previous reports in rats. Df(16)A(+/-) mice, which are impaired in the acquisition of the task, showed drastically reduced synchrony, measured both by phase-locking of prefrontal cells to hippocampal theta oscillations and by coherence of prefrontal and hippocampal local field potentials. Furthermore, the magnitude of hippocampal-prefrontal coherence at the onset of training could be used to predict the time it took the Df(16)A(+/-) mice to learn the task and increased more slowly during task acquisition. These data suggest how the deficits in functional connectivity observed in patients with schizophrenia may be realized at the single-neuron level. Our findings further suggest that impaired long-range synchrony of neural activity is one consequence of the 22q11.2 deletion and may be a fundamental component of the pathophysiology underlying schizophrenia.

Bridging the gene-behavior divide through neuroimaging deletion syndromes: Velocardiofacial (22q11.2 Deletion) and Williams (7q11.23 Deletion) syndromes

Investigating the relationship between genes and the neural substrates of complex human behavior promises to provide essential insight into the pathophysiology of mental disorders. One approach to this inquiry is through neuroimaging of individuals with microdeletion syndromes that manifest in specific neuropsychiatric phenotypes. Both Velocardiofacial syndrome (VCFS) and Williams syndrome (WS) involve haploinsufficiency of a relatively small set of identified genes on the one hand and association with distinct, clinically relevant behavioral and cognitive profiles on the other hand. In VCFS, there is a deletion in chromosomal region 22q11.2 and a resultant predilection toward psychosis, poor arithmetic proficiency, and low performance intelligence quotients. In WS, there is a deletion in chromosomal region 7q11.23 and a resultant predilection toward hypersociability, non-social anxiety, impaired visuospatial construction, and often intellectual impairment. Structural and functional neuroimaging studies have begun not only to map these well-defined genetic alterations to systems-level brain abnormalities, but also to identify relationships between neural phenotypes and particular genes within the critical deletion regions. Though neuroimaging of both VCFS and WS presents specific, formidable methodological challenges, including comparison subject selection and accounting for neuroanatomical and vascular anomalies in patients, and many questions remain, the literature to date on these syndromes, reviewed herein, constitutes a fruitful "bottom-up" approach to defining gene-brain relationships.

The effects of gender and catechol O-methyltransferase (COMT) Val108/158Met polymorphism on emotion regulation in velo-cardio-facial syndrome (22q11.2 deletion syndrome): An fMRI study

Velo-cardio-facial syndrome (VCFS) is caused by a micro-deletion of over 40 genes at the q11.2 locus of chromosome 22 and is a risk factor for the development of schizophrenia and other psychiatric disorders. COMT, one of the genes located in the deleted region, has been considered as a major candidate gene for genetic susceptibility in psychiatric diseases. Its functional polymorphism Val108/158Met has been shown to affect prefrontal function and working memory and has been associated with emotional dysregulation. We utilized a functional magnetic resonance imaging (fMRI) event-related paradigm to asses COMT genotype and gender-moderated effects on the neural activation that are elicited by viewing emotionally salient images charged with pleasant, unpleasant, and neutral content. Since estrogen down-regulates COMT activity resulting in lower COMT activity in women than men, we hypothesized an allele-by-gender interaction effect on neural activation. Participants included 43 VCFS individuals (Val/male=9, Val/female=17, Met/male=9, Met/female=8). We observed a gender effect on processing positive emotions, in that girls activated the cingulate gyrus more than boys did. We further observed a significant gender-by-allele interaction effect on neural function specific to the frontal lobe during the processing of pleasant stimuli, and specific to limbic regions during the processing of unpleasant stimuli. Our results suggest that in VCFS, the effect of the COMT Val108/158Met polymorphism is moderated by gender during the processing of emotional stimuli and could contribute to the understanding of the way in which this COMT polymorphism affects vulnerability to neuropsychiatric disorders.

Associations between performance on the Rey-Osterrieth Complex Figure and regional brain volumes in children with and without velocardiofacial syndrome

Ninety-two children with velocardiofacial syndrome (VCFS), a genetic disorder caused by a microdeletion of chromosome 22q11.2 and an age, race, and gender-ratio comparable sample of 59 control participants were included in the project. Participants received an MRI as well as a comprehensive neuropsychological battery; the primary outcome measure in the current report is the Rey-Osterrieth Complex Figure (ROCF). Children with VCFS performed less well on the ROCF and have lower whole brain volume compared to controls. After controlling for whole brain volume differences, children with VCFS have bilaterally less parietal lobe gray and white matter yet more frontal lobe white matter. Brain-behavior relationships include: (a) for both groups, parietal volumes (both gray and white matter) predicted ROCF Copy Organization performance and frontal volumes (both gray and white matter) predicted ROCF Copy Accuracy performance; (b) for controls, frontal white matter also predicted ROCF Copy Organization performance; (c) ROCF Recall Organization performance was best predicted by frontal gray matter volume only in our controls; ROCF Recall Accuracy performance was best predicted by frontal gray matter volume in both groups; and (d) in children with VCFS, performance on the ROCF-Copy Structural Elements Accuracy scale was predicted by right hemisphere white matter volume. Our hypotheses were also retested using IQ-matched and whole brain volume-matched subsamples. Identical results were obtained in these analyses. Assumptions about the organization of and the localization of the brain structures that subserve specific cognitive functions in the typically developing brain may not apply in the abnormally developing brain.