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

Event-related potential (ERP) markers of 22q11.2 deletion syndrome and associated psychosis

22q11.2 deletion syndrome (22q11.2DS) is a multisystemic disorder characterized by a wide range of clinical features, ranging from life-threatening to less severe conditions. One-third of individuals with the deletion live with mild to moderate intellectual disability; approximately 60% meet criteria for at least one psychiatric condition.22q11.2DS has become an important model for several medical, developmental, and psychiatric disorders. We have been particularly interested in understanding the risk for psychosis in this population: Approximately 30% of the individuals with the deletion go on to develop schizophrenia. The characterization of cognitive and neural differences between those individuals who develop schizophrenia and those who do not, despite being at genetic risk, holds important promise in what pertains to the clarification of paths to disease and to the development of tools for early identification and intervention.Here, we review our previous event-related potential (ERP) findings as potential markers for 22q11.2DS and the associated risk for psychosis, while discussing others' work. We focus on auditory processing (auditory-evoked potentials, auditory adaptation, and auditory sensory memory), visual processing (visual-evoked potentials and visual adaptation), and inhibition and error monitoring.The findings discussed suggest basic mechanistic and disease process effects on neural processing in 22q11.2DS that are present in both early sensory and later cognitive processing, with possible implications for phenotype. In early sensory processes, both during auditory and visual processing, two mechanisms that impact neural responses in opposite ways seem to coexist-one related to the deletion, which increases brain responses; another linked to psychosis, decreasing neural activity. Later, higher-order cognitive processes may be equally relevant as markers for psychosis. More specifically, we argue that components related to error monitoring may hold particular promise in the study of risk for schizophrenia in the general population.

Genetic underpinnings of schizophrenia-related electroencephalographical intermediate phenotypes: A systematic review and meta-analysis

Although substantial research into genetics of psychotic disorders has been conducted, a large proportion of their genetic architecture has remained unresolved. Electroencephalographical intermediate phenotypes (EIP) have the potential to constitute a valuable tool when studying genetic risk loci for schizophrenia, in particular P3b amplitude, P50 suppression, mismatch negativity (MMN) and resting state power spectra of the electroencephalogram (EEG). Here, we systematically reviewed studies investigating the association of single nucleotide polymorphisms (SNPs) with these EIPs and meta-analysed them when appropriate. We retrieved 45 studies (N = 34,971 study participants). Four SNPs investigated in more than one study were genome-wide significant for an association with schizophrenia and three were genome-wide suggestive, based on a lookup in the influential 2014 GWAS (Ripke et al., 2014). However, in our meta-analyses, rs1625579 failed to reach a statistically significant association with p3b amplitude decrease and rs4680 risk allele carrier status was not associated with p3b amplitude decrease or with impaired p50 suppression. In conclusion, evidence for SNP associations with EIPs remains limited to individual studies. Careful selection of EIPs and SNPs, combined with consistent reporting of effect sizes, directions of effect and p-values would aid future meta-analyses.

Genetic Determinants of Gating Functions: Do We Get Closer to Understanding Schizophrenia Etiopathogenesis?

Deficits in the gating of sensory stimuli, i.e., the ability to suppress the processing of irrelevant sensory input, are considered to play an important role in the pathogenesis of several neuropsychiatric disorders, in particular schizophrenia. Gating is disrupted both in schizophrenia patients and their unaffected relatives, suggesting that gating deficit may represent a biomarker associated with a genetic liability to the disorder. To assess the strength of the evidence for the etiopathogenetic links between genetic variation, gating efficiency, and schizophrenia, we carried out a systematic review of human genetic association studies of sensory gating (suppression of the P50 component of the auditory event-related brain potential) and sensorimotor gating (prepulse inhibition of the acoustic startle response). Sixty-three full-text articles met the eligibility criteria for inclusion in the review. In total, 117 genetic variants were reported to be associated with gating functions: 33 variants for sensory gating, 80 variants for sensorimotor gating, and four variants for both sensory and sensorimotor gating. However, only five of these associations (four for prepulse inhibition-CHRNA3 rs1317286, COMT rs4680, HTR2A rs6311, and TCF4 rs9960767, and one for P50 suppression-CHRNA7 rs67158670) were consistently replicated in independent samples. Although these variants and genes were all implicated in schizophrenia in research studies, only two polymorphisms (HTR2A rs6311 and TCF4 rs9960767) were also reported to be associated with schizophrenia at a meta-analytic or genome-wide level of evidence. Thus, although gating is widely considered as an important endophenotype of schizophrenia, these findings demonstrate that evidence for a common genetic etiology of impaired gating functions and schizophrenia is yet unsatisfactory, warranting further studies in this field.

Abnormal Development and Dysconnectivity of Distinct Thalamic Nuclei in Patients With 22q11.2 Deletion Syndrome Experiencing Auditory Hallucinations

BACKGROUND

Several studies in patients with schizophrenia have demonstrated an abnormal thalamic volume and thalamocortical connectivity. Specifically, hyperconnectivity with somatosensory areas has been related to the presence of auditory hallucinations (AHs). The 22q11.2 deletion syndrome is a neurogenetic disorder conferring proneness to develop schizophrenia, and deletion carriers (22qdel carriers) experience hallucinations to a greater extent than the general population.

METHODS

We acquired 442 consecutive magnetic resonance imaging scans from 120 22qdel carriers and 110 control subjects every 3 years (age range: 8-35 years). The volume of thalamic nuclei was obtained with FreeSurfer and was compared between 22qdel carriers and control subjects and between 22qdel carriers with and without AHs. In a subgroup of 76 22qdel carriers, we evaluated the functional connectivity between thalamic nuclei affected in patients experiencing AHs and cortical regions.

RESULTS

As compared with control subjects, 22qdel carriers had lower and higher volumes of nuclei involved in sensory processing and cognitive functions, respectively. 22qdel carriers with AHs had a smaller volume of the medial geniculate nucleus, with deviant trajectories showing a steeper volume decrease from childhood with respect to those without AHs. Moreover, we showed an aberrant development of nuclei intercalated between the prefrontal cortex and hippocampus (the anteroventral and medioventral reuniens nuclei) and hyperconnectivity of the medial geniculate nucleus and anteroventral nucleus with the auditory cortex and Wernicke's area.

CONCLUSIONS

The increased connectivity of the medial geniculate nucleus and anteroventral nucleus to the auditory cortex might be interpreted as a lack of maturation of thalamocortical connectivity. Overall, our findings point toward an aberrant development of thalamic nuclei and an immature pattern of connectivity with temporal regions in relation to AHs.

Assessing auditory processing endophenotypes associated with Schizophrenia in individuals with 22q11.2 deletion syndrome

22q11.2 Deletion Syndrome (22q11.2DS) is the strongest known molecular risk factor for schizophrenia. Brain responses to auditory stimuli have been studied extensively in schizophrenia and described as potential biomarkers of vulnerability to psychosis. We sought to understand whether these responses might aid in differentiating individuals with 22q11.2DS as a function of psychotic symptoms, and ultimately serve as signals of risk for schizophrenia. A duration oddball paradigm and high-density electrophysiology were used to test auditory processing in 26 individuals with 22q11.2DS (13-35 years old, 17 females) with varying degrees of psychotic symptomatology and in 26 age- and sex-matched neurotypical controls (NT). Presentation rate varied across three levels, to examine the effect of increasing demands on memory and the integrity of sensory adaptation. We tested whether N1 and mismatch negativity (MMN), typically reduced in schizophrenia, related to clinical/cognitive measures, and how they were affected by presentation rate. N1 adaptation effects interacted with psychotic symptomatology: Compared to an NT group, individuals with 22q11.2DS but no psychotic symptomatology presented larger adaptation effects, whereas those with psychotic symptomatology presented smaller effects. In contrast, individuals with 22q11.2DS showed increased effects of presentation rate on MMN amplitude, regardless of the presence of symptoms. While IQ and working memory were lower in the 22q11.2DS group, these measures did not correlate with the electrophysiological data. These findings suggest the presence of two distinct mechanisms: One intrinsic to 22q11.2DS resulting in increased N1 and MMN responses; another related to psychosis leading to a decreased N1 response.

Molecular genetics of 22q11.2 deletion syndrome

The 22q11.2 deletion syndrome (22q11.2DS) is a congenital malformation and neuropsychiatric disorder caused by meiotic chromosome rearrangements. One of the goals of this review is to summarize the current state of basic research studies of 22q11.2DS. It highlights efforts to understand the mechanisms responsible for the 22q11.2 deletion that occurs in meiosis. This mechanism involves the four sets of low copy repeats (LCR22) that are dispersed in the 22q11.2 region and the deletion is mediated by nonallelic homologous recombination events. This review also highlights selected genes mapping to the 22q11.2 region that may contribute to the typical clinical findings associated with the disorder and explain that mutations in genes on the remaining allele can uncover rare recessive conditions. Another important aspect of 22q11.2DS is the existence of phenotypic heterogeneity. While some patients are mildly affected, others have severe medical, cognitive, and/or psychiatric challenges. Variability may be due in part to the presence of genetic modifiers. This review discusses current genome-wide efforts to identify such modifiers that could shed light on molecular pathways required for normal human development, cognition or behavior.

Abnormal development of early auditory processing in 22q11.2 Deletion Syndrome

The 22q11.2 Deletion Syndrome (22q11.2 DS) is one of the highest genetic risk factors for the development of schizophrenia spectrum disorders. In schizophrenia, reduced amplitude of the frequency mismatch negativity (fMMN) has been proposed as a promising neurophysiological marker for progressive brain pathology. In this longitudinal study in 22q11.2 DS, we investigate the progression of fMMN between childhood and adolescence, a vulnerable period for brain maturation. We measured evoked potentials to auditory oddball stimuli in the same sample of 16 patients with 22q11.2 DS and 14 age-matched controls in childhood and adolescence. In addition, we cross-sectionally compared an increased sample of 51 participants with 22q11.2 DS and 50 controls divided into two groups (8-14 and 14-20 years). The reported results are obtained using the fMMN difference waveforms. In the longitudinal design, the 22q11.2 deletion carriers exhibit a significant reduction in amplitude and a change in topographic patterns of the mismatch negativity response from childhood to adolescence. The same effect, reduced mismatch amplitude in adolescence, while preserved during childhood, is observed in the cross-sectional study. These results point towards functional changes within the brain network responsible for the fMMN. In addition, the adolescents with 22q11.2 DS displayed a significant increase in amplitude over central electrodes during the auditory N1 component. No such differences, reduced mismatch response nor increased N1, were observed in the typically developing group. These findings suggest different developmental trajectories of early auditory sensory processing in 22q11.2 DS and functional changes that emerge during the critical period of increased risk for schizophrenia spectrum disorders.

Individuals with 22q11.2 deletion syndrome show intact prediction but reduced adaptation in responses to repeated sounds: Evidence from Bayesian mapping

One of the most common copy number variants, the 22q11.2 microdeletion, confers an increased risk for schizophrenia. Since schizophrenia has been associated with an aberrant neural response to repeated stimuli through both reduced adaptation and prediction, we here hypothesized that this may also be the case in nonpsychotic individuals with a 22q11.2 deletion. We recorded high-density EEG from 19 individuals with 22q11.2 deletion syndrome (12-25 years), as well as 27 healthy volunteers with comparable age and sex distribution, while they listened to a sequence of sounds arranged in a roving oddball paradigm. Using posterior probability maps and dynamic causal modelling we tested three different models accounting for repetition dependent changes in cortical responses as well as in effective connectivity; namely an adaptation model, a prediction model, and a model including both adaptation and prediction. Repetition-dependent changes were parametrically modulated by a combination of adaptation and prediction and were apparent in both cortical responses and in the underlying effective connectivity. This effect was reduced in individuals with a 22q11.2 deletion and was negatively correlated with negative symptom severity. Follow-up analysis showed that the reduced effect of the combined adaptation and prediction model seen in individuals with 22q11.2 deletion was driven by reduced adaptation rather than prediction failure. Our findings suggest that adaptation is reduced in individuals with a 22q11.2 deletion, which can be interpreted in light of the framework of predictive coding as a failure to suppress prediction errors.

Risk gene-set and pathways in 22q11.2 deletion-related schizophrenia: a genealogical molecular approach

The 22q11.2 deletion is a strong, but insufficient, "first hit" genetic risk factor for schizophrenia (SZ). We attempted to identify "second hits" from the entire genome in a unique multiplex 22q11.2 deletion syndrome (DS) family. Bioinformatic analysis of whole-exome sequencing and comparative-genomic hybridization array identified de novo and inherited, rare and damaging variants, including copy number variations, outside the 22q11.2 region. A specific 22q11.2-haplotype was associated with psychosis. The interaction of the identified "second hits" with the 22q11.2 haploinsufficiency may affect neurodevelopmental processes, including neuron projection, cytoskeleton activity, and histone modification in 22q11.2DS-ralated psychosis. A larger load of variants, involved in neurodevelopment, in combination with additional molecular events that affect sensory perception, olfactory transduction and G-protein-coupled receptor signaling may account for the development of 22q11.2DS-related SZ. Comprehensive analysis of multiplex families is a promising approach to the elucidation of the molecular pathophysiology of 22q11.2DS-related SZ with potential relevance to treatment.

Musical auditory processing, cognition, and psychopathology in 22q11.2 deletion syndrome

Chromosome 22q11.2 deletion syndrome (22q11DS) is associated with impairment in multiple domains of cognition and risk for several psychiatric disorders. Musical auditory processing is highly heritable, and is impaired in individuals with schizophrenia and other neurodevelopmental disorders, but has never been studied in 22q11DS, notwithstanding anecdotal evidence of its sparing. We aimed to characterize musical auditory processing in 22q11DS and explore potential relationships with other cognitive domains, musical engagement, and psychiatric disorders. The Distorted Tunes Task and Global Musical Sophistication Index were used to assess pitch discrimination and general musical engagement in 58 individuals with 22q11DS aged 8-29 years. Psychopathology was assessed with sections from the modified Schedule for Affective Disorders and Schizophrenia for School-Age Children and the Structured Interview for Prodromal Syndromes. The Penn computerized neurocognitive battery (CNB) examined four domains of cognition (executive functioning, episodic memory, complex cognition, and social cognition). Significant musical auditory processing impairment and reduced musical engagement were found in individuals with 22q11DS. However, deficits in musical auditory processing were not associated with reduced musical engagement. After covarying for age and sex, episodic memory and overall CNB performance accuracy were significantly related to performance in musical auditory processing. There were no relationships between musical auditory processing and presence of any psychiatric diagnoses. Individuals with 22q11DS experience significant deficits in musical auditory processing and reduced musical engagement. Pitch discrimination is associated with overall cognitive ability, but appears to be largely independent of psychiatric illness.

Catatonia in Children and Adolescents: A High Rate of Genetic Conditions

Pediatric catatonia is a rare and severe neuropsychiatric syndrome. We previously reported, in 58 children and adolescents with catatonia, a high prevalence (up to 20%) of medical conditions, some of which have specific treatments.¹ Here we extend the cohort inclusion and report the first systematic molecular genetic data for this syndrome. Among the 89 patients consecutively admitted for catatonia (according to the pediatric catatonia rating scale)² between 1993 and 2014, we identify 51 patients (57.3%) who had genetic laboratory testing, of whom 37 had single nucleotide polymorphism (SNP) microarray tests for CNVs and 14 had routine genetic explorations (karyotyping and searches for specific chromosomal abnormalities by fluorescence in situ hybridization [FISH]) or a specific diagnosis test based on clinical history. To assess the causality of observed genetic findings in each patient, we used a causality assessment score (CAUS)³ including 5 causality-support criteria on a 3-point scale (0 = absent; 1 = moderate; 2 = high): the existence of similar cases in the literature; the presence of a clinical contributing factor; the presence of a biological contributing factor; the presence of other paraclinical symptoms; and response to a specific treatment related to the suspected genetic or medical condition.

Altered auditory processing and effective connectivity in 22q11.2 deletion syndrome

22q11.2 deletion syndrome (22q11.2DS) is one of the most common copy number variants and confers a markedly increased risk for schizophrenia. As such, 22q11.2DS is a homogeneous genetic liability model which enables studies to delineate functional abnormalities that may precede disease onset. Mismatch negativity (MMN), a brain marker of change detection, is reduced in people with schizophrenia compared to healthy controls. Using dynamic causal modelling (DCM), previous studies showed that top-down effective connectivity linking the frontal and temporal cortex is reduced in schizophrenia relative to healthy controls in MMN tasks. In the search for early risk-markers for schizophrenia we investigated the neural basis of change detection in a group with 22q11.2DS. We recorded high-density EEG from 19 young non-psychotic 22q11.2 deletion carriers, as well as from 27 healthy non-carriers with comparable age distribution and sex ratio, while they listened to a sequence of sounds arranged in a roving oddball paradigm. Despite finding no significant reduction in the MMN responses, whole-scalp spatiotemporal analysis of responses to the tones revealed a greater fronto-temporal N1 component in the 22q11.2 deletion carriers. DCM showed reduced intrinsic connection within right primary auditory cortex as well as in the top-down, connection from the right inferior frontal gyrus to right superior temporal gyrus for 22q11.2 deletion carriers although not surviving correction for multiple comparison. We discuss these findings in terms of reduced adaptation and a general increased sensitivity to tones in 22q11.2DS.

The Proline Cycle As a Potential Cancer Therapy Target

Interest in how proline contributes to cancer biology is expanding because of the emerging role of a novel proline metabolic cycle in cancer cell survival, proliferation, and metastasis. Proline biosynthesis and degradation involve the shared intermediate Δ1-pyrroline-5-carboxylate (P5C), which forms l-glutamate-γ-semialdehyde (GSAL) in a reversible non-enzymatic reaction. Proline is synthesized from glutamate or ornithine through GSAL/P5C, which is reduced to proline by P5C reductase (PYCR) in a NAD(P)H-dependent reaction. The degradation of proline occurs in the mitochondrion and involves two oxidative steps catalyzed by proline dehydrogenase (PRODH) and GSAL dehydrogenase (GSALDH). PRODH is a flavin-dependent enzyme that couples proline oxidation with reduction of membrane-bound quinone, while GSALDH catalyzes the NAD+-dependent oxidation of GSAL to glutamate. PRODH and PYCR form a metabolic relationship known as the proline-P5C cycle, a novel pathway that impacts cellular growth and death pathways. The proline-P5C cycle has been implicated in supporting ATP production, protein and nucleotide synthesis, anaplerosis, and redox homeostasis in cancer cells. This Perspective details the structures and reaction mechanisms of PRODH and PYCR and the role of the proline-P5C cycle in cancer metabolism. A major challenge in the field is to discover inhibitors that specifically target PRODH and PYCR isoforms for use as tools for studying proline metabolism and the functions of the proline-P5C cycle in cancer. These molecular probes could also serve as lead compounds in cancer drug discovery targeting the proline-P5C cycle.

Deletion size analysis of 1680 22q11.2DS subjects identifies a new recombination hotspot on chromosome 22q11.2

Recurrent, de novo, meiotic non-allelic homologous recombination events between low copy repeats, termed LCR22s, leads to the 22q11.2 deletion syndrome (22q11.2DS; velo-cardio-facial syndrome/DiGeorge syndrome). Although most 22q11.2DS patients have a similar sized 3 million base pair (Mb), LCR22A-D deletion, some have nested LCR22A-B or LCR22A-C deletions. Our goal is to identify additional recurrent 22q11.2 deletions associated with 22q11.2DS, serving as recombination hotspots for meiotic chromosomal rearrangements. Here, using data from Affymetrix 6.0 microarrays on 1680 22q11.2DS subjects, we identified what appeared to be a nested proximal 22q11.2 deletion in 38 (2.3%) of them. Using molecular and haplotype analyses from 14 subjects and their parent(s) with available DNA, we found essentially three types of scenarios to explain this observation. In eight subjects, the proximal breakpoints occurred in a small sized 12 kb LCR distal to LCR22A, referred to LCR22A+, resulting in LCR22A+-B or LCR22A+-D deletions. Six of these eight subjects had a nested 22q11.2 deletion that occurred during meiosis in a parent carrying a benign 0.2 Mb duplication of the LCR22A-LCR22A+ region with a breakpoint in LCR22A+. Another six had a typical de novo LCR22A-D deletion on one allele and inherited the LCR22A-A+ duplication from the other parent thus appearing on microarrays to have a nested deletion. LCR22A+ maps to an evolutionary breakpoint between mice and humans and appears to serve as a local hotspot for chromosome rearrangements on 22q11.2.

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.

Using EEG-Guided Basket and Umbrella Trials in Psychiatry: A Precision Medicine Approach for Cognitive Impairment in Schizophrenia

Due to advances over the last several decades, many fields of medicine are moving toward a precision medicine approach where treatments are tailored to nuanced patient factors. While in some disciplines these innovations are commonplace leading to unique biomarker-guided experimental medicine trials, there are no such analogs in psychiatry. In this brief review, we will overview two unique biomarker-guided trial designs for future use in psychiatry: basket and umbrella trials. We will illustrate how such trials could be useful in psychiatry using schizophrenia as a candidate illness, the EEG measure mismatch negativity as the candidate biomarker, and cognitive impairment as the target disease dimension.

Discovery of the Membrane Binding Domain in Trifunctional Proline Utilization A

Escherichia coli proline utilization A (EcPutA) is the archetype of trifunctional PutA flavoproteins, which function both as regulators of the proline utilization operon and bifunctional enzymes that catalyze the four-electron oxidation of proline to glutamate. EcPutA shifts from a self-regulating transcriptional repressor to a bifunctional enzyme in a process known as functional switching. The flavin redox state dictates the function of EcPutA. Upon proline oxidation, the flavin becomes reduced, triggering a conformational change that causes EcPutA to dissociate from the put regulon and bind to the cellular membrane. Major structure/function domains of EcPutA have been characterized, including the DNA-binding domain, proline dehydrogenase (PRODH) and l-glutamate-γ-semialdehyde dehydrogenase catalytic domains, and an aldehyde dehydrogenase superfamily fold domain. Still lacking is an understanding of the membrane-binding domain, which is essential for EcPutA catalytic turnover and functional switching. Here, we provide evidence for a conserved C-terminal motif (CCM) in EcPutA having a critical role in membrane binding. Deletion of the CCM or replacement of hydrophobic residues with negatively charged residues within the CCM impairs EcPutA functional and physical membrane association. Furthermore, cell-based transcription assays and limited proteolysis indicate that the CCM is essential for functional switching. Using fluorescence resonance energy transfer involving dansyl-labeled liposomes, residues in the α-domain are also implicated in membrane binding. Taken together, these experiments suggest that the CCM and α-domain converge to form a membrane-binding interface near the PRODH domain. The discovery of the membrane-binding region will assist efforts to define flavin redox signaling pathways responsible for EcPutA functional switching.

Cytosolic Accumulation of L-Proline Disrupts GABA-Ergic Transmission through GAD Blockade

Proline dehydrogenase (PRODH), which degrades L-proline, resides within the schizophrenia-linked 22q11.2 deletion suggesting a role in disease. Supporting this, elevated L-proline levels have been shown to increase risk for psychotic disorders. Despite the strength of data linking PRODH and L-proline to neuropsychiatric diseases, targets of disease-relevant concentrations of L-proline have not been convincingly described. Here, we show that Prodh-deficient mice with elevated CNS L-proline display specific deficits in high-frequency GABA-ergic transmission and gamma-band oscillations. We find that L-proline is a GABA-mimetic and can act at multiple GABA-ergic targets. However, at disease-relevant concentrations, GABA-mimesis is limited to competitive blockade of glutamate decarboxylase leading to reduced GABA production. Significantly, deficits in GABA-ergic transmission are reversed by enhancing net GABA production with the clinically relevant compound vigabatrin. These findings indicate that accumulation of a neuroactive metabolite can lead to molecular and synaptic dysfunction and help to understand mechanisms underlying neuropsychiatric disease.

Engineering a trifunctional proline utilization A chimaera by fusing a DNA-binding domain to a bifunctional PutA

Proline utilization A (PutA) is a bifunctional flavoenzyme with proline dehydrogenase (PRODH) and Δ1-pyrroline-5-carboxylate (P5C) dehydrogenase (P5CDH) domains that catalyses the two-step oxidation of proline to glutamate. Trifunctional PutAs also have an N-terminal ribbon-helix-helix (RHH) DNA-binding domain and moonlight as autogenous transcriptional repressors of the put regulon. A unique property of trifunctional PutA is the ability to switch functions from DNA-bound repressor to membrane-associated enzyme in response to cellular nutritional needs and proline availability. In the present study, we attempt to construct a trifunctional PutA by fusing the RHH domain of Escherichia coli PutA (EcRHH) to the bifunctional Rhodobacter capsulatus PutA (RcPutA) in order to explore the modular design of functional switching in trifunctional PutAs. The EcRHH-RcPutA chimaera retains the catalytic properties of RcPutA while acquiring the oligomeric state, quaternary structure and DNA-binding properties of EcPutA. Furthermore, the EcRHH-RcPutA chimaera exhibits proline-induced lipid association, which is a fundamental characteristic of functional switching. Unexpectedly, RcPutA lipid binding is also activated by proline, which shows for the first time that bifunctional PutAs exhibit a limited form of functional switching. Altogether, these results suggest that the C-terminal domain (CTD), which is conserved by trifunctional PutAs and certain bifunctional PutAs, is essential for functional switching in trifunctional PutAs.

The dysconnection hypothesis (2016)

Twenty years have passed since the dysconnection hypothesis was first proposed (Friston and Frith, 1995; Weinberger, 1993). In that time, neuroscience has witnessed tremendous advances: we now live in a world of non-invasive neuroanatomy, computational neuroimaging and the Bayesian brain. The genomics era has come and gone. Connectomics and large-scale neuroinformatics initiatives are emerging everywhere. So where is the dysconnection hypothesis now? This article considers how the notion of schizophrenia as a dysconnection syndrome has developed - and how it has been enriched by recent advances in clinical neuroscience. In particular, we examine the dysconnection hypothesis in the context of (i) theoretical neurobiology and computational psychiatry; (ii) the empirical insights afforded by neuroimaging and associated connectomics - and (iii) how bottom-up (molecular biology and genetics) and top-down (systems biology) perspectives are converging on the mechanisms and nature of dysconnections in schizophrenia.

Evidence that COMT genotype and proline interact on negative-symptom outcomes in schizophrenia and bipolar disorder

Elevated peripheral proline is associated with psychiatric disorders, and there is evidence that proline is a neuromodulator. The proline dehydrogenase (PRODH) gene, which encodes the enzyme that catalyzes proline catabolism, maps to human chromosome 22q11.2, a region conferring risk of schizophrenia. In the Prodh-null mouse, an interaction between elevated peripheral proline and another 22q11.2 gene, catechol-O-methyltransferase (COMT), on neurotransmission and behavior has been reported. We explored the relationship between fasting plasma proline levels and COMT Val(158)Met genotype on symptoms (positive, negative and total) in schizophrenia patients. In an exploratory study we also examined symptom change in patients with bipolar disorder. There was a significant interaction between peripheral proline and COMT on negative symptoms in schizophrenia (P<0.0001, n=95). In COMT Val/Val patients, high proline was associated with low Scale for the Assessment of Negative Symptom (SANS) scores. In contrast, high proline was associated with high SANS scores in patients carrying a Met allele. The relationship between proline and COMT also appears to modify negative symptoms across psychiatric illness. In bipolar disorder, a significant interaction was also observed on negative-symptom change (P=0.007, n=43). Negative symptoms are intractable and largely unaddressed by current medications. These data indicate a significant interaction between peripheral proline and COMT genotype, influencing negative symptoms in schizophrenia and bipolar disorder. That high proline has converse effects on symptoms by COMT genotype, may have implications for therapeutic decisions.

Cognitive phenotype and psychiatric disorder in 22q11.2 deletion syndrome: A review

The behavioural phenotype of 22q11.2 deletion syndrome syndrome (22q11DS), one of the most common human multiple anomaly syndromes, frequently includes intellectual disability (ID) together with high risk of diagnosis of psychotic disorders including schizophrenia. Candidate cognitive endophenotypes include problems with retrieval of contextual information from memory and in executive control and focussing of attention. 22q11DS may offer a model of the relationship between ID and risk of psychiatric disorder. This paper reviews research on the relationship between the cognitive phenotype and the development of psychiatric disorders in 22q11DS. Aspects of cognitive function including verbal I.Q., visual memory, and executive function, are associated with mental health outcome in people with 22q11DS. This relationship may result from a common neurobiological basis for the cognitive difficulties and psychiatric disorders. Some of the cognitive difficulties experienced by people with 22q11DS, especially in attention, memory retrieval, and face processing, may, however, in themselves constitute risk factors for development of hallucinations and paranoid delusions. Future research into factors leading to psychiatric disorder in people with 22q11DS should include assessment of social and psychological factors including life events, symptoms associated with trauma, attachment, and self-esteem, which together with cognitive risk factors may mediate mental health outcome.

The use of two different MLPA kits in 22q11.2 deletion syndrome

22q11.2 deletion syndrome (22q11DS) is one of the most common recurrent copy-number variant disorder, caused by a microdeletion in chromosome band 22q11.2 and occurring with a population prevalence of 1 in 2000. Until today there has been no evidence that the size of the deletion has an influence on the clinical phenotype. Most studies report that 22q11DS is associated with mild or borderline intellectual disability. There are a limited number of reports on 22q11DS subjects with moderate or severe intellectual disability. In this study we describe 63 adult patients with 22q11DS, including 22q11DS patients functioning at a moderate to severe intellectual disabled level. Deletion size was established with an experimental Multiplex ligation-dependent probe amplification (MLPA) mixture (P324) in addition to the commonly used MLPA kit (P250). We compared deletion size with intellectual functioning and presence of psychotic symptoms during life. The use of the experimental MLPA kit gives extra information on deletion size, only when combined with the common MLPA kit. We were able to detect eleven atypical deletions and in two cases the deletion size was shorter than all other "typical ones". We conclude that the use of the experimental kit P324 gives extra information about the deletion size, but only when used together with the standard P250 kit. We did not found any relation of deletion size with intelligence or presence of psychosis.

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.

22q11.21 Deletion Syndromes: A Review of Proximal, Central, and Distal Deletions and Their Associated Features

Chromosome 22q11.21 contains a cluster of low-copy repeats (LCRs), referred to as LCR22A-H, that mediate meiotic non-allelic homologous recombination, resulting in either deletion or duplication of various intervals in the region. The deletion of the DiGeorge/velocardiofacial syndrome interval LCR22A-D is the most common recurrent microdeletion in humans, with an estimated incidence of ∼1:4,000 births. Deletion of other intervals in 22q11.21 have also been described, but the literature is often confusing, as the terms 'proximal', 'nested', 'distal', and 'atypical' have all been used to describe various of the other intervals. Individuals with deletions tend to have features with widely variable expressivity, even among families. This review concisely delineates each interval and classifies the reported literature accordingly.

Association of COMT and PRODH gene variants with intelligence quotient (IQ) and executive functions in 22q11.2DS subjects

The 22q11.2 deletion syndrome (22q11.2DS) carries the highest genetic risk factor for the development of schizophrenia. We investigated the association of genetic variants in two schizophrenia candidate genes with executive function (EF) and IQ in 22q11.2DS individuals. Ninety two individuals with 22q11.2 deletion were studied for the genetic association between COMT and PRODH variants and EF and IQ. Subjects were divided into children (under 12 years old), adolescents (between 12 and 18 years old) and adults (older than 18 years), and genotyped for the COMT Val158Met (rs4680) and PRODH Arg185Trp (rs4819756) polymorphisms. The participants underwent psychiatric evaluation and EF assessment. Our main finding is a significant influence of the COMT Val158Met polymorphism on both IQ and EF performance. Specifically, 22q11.2DS subjects with Met allele displayed higher IQ scores in all age groups compared to Val carriers, reaching significance in both adolescents and adults. The Met allele carriers performed better than Val carriers in EF tasks, being statistically significant in the adult group. PRODH Arg185Trp variant did not affect IQ or EF in our 22q11.2DS cohort. In conclusion, functional COMT variant, but not PRODH, affects IQ and EF in 22q11.2DS subjects during neurodevelopment with a maximal effect at adulthood. Future studies should monitor the cognitive performance of the same individuals from childhood to old age.

22q11 deletion syndrome: a review of the neuropsychiatric features and their neurobiological basis

The 22q11.2 deletion syndrome (22q11DS) is caused by an autosomal dominant microdeletion of chromosome 22 at the long arm (q) 11.2 band. The 22q11DS is among the most clinically variable syndromes, with more than 180 features related with the deletion, and is associated with an increased risk of psychiatric disorders, accounting for up to 1%-2% of schizophrenia cases. In recent years, several genes located on chromosome 22q11 have been linked to schizophrenia, including those encoding catechol-O-methyltransferase and proline dehydrogenase, and the interaction between these and other candidate genes in the deleted region is an important area of research. It has been suggested that haploinsufficiency of some genes within the 22q11.2 region may contribute to the characteristic psychiatric phenotype and cognitive functioning of schizophrenia. Moreover, an extensive literature on neuroimaging shows reductions of the volumes of both gray and white matter, and these findings suggest that this reduction may be predictive of increased risk of prodromal psychotic symptoms in 22q11DS patients. Experimental and standardized cognitive assessments alongside neuroimaging may be important to identify one or more endophenotypes of schizophrenia, as well as a predictive prodrome that can be preventively treated during childhood and adolescence. In this review, we summarize recent data about the 22q11DS, in particular those addressing the neuropsychiatric and cognitive phenotypes associated with the deletion, underlining the recent advances in the studies about the genetic architecture of the syndrome.