α-Synuclein and Neuronal Cell Death

Parkinson’s disease (PD) is a progressive neurodegenerative disorder affecting ～1 % of people over the age of 65. Neuropathological hallmarks of PD are prominent loss of dopaminergic (DA) neurons in the substantia nigra and formation of intraneuronal protein inclusions termed Lewy bodies, composed mainly of α-synuclein (αSyn). Missense mutations in αSyn gene giving rise to production of degradation-resistant mutant proteins or multiplication of wild-type αSyn gene allele can cause rare inherited forms of PD. Therefore, the existence of abnormally high amount of αSyn protein is considered responsible for the DA neuronal death in PD. Normally, αSyn protein localizes to presynaptic terminals of neuronal cells, regulating the neurotransmitter release through the modulation of assembly of soluble N-ethylmaleimide-sensitive factor attachment protein receptor complex. On the other hand, of note, pathological examinations on the recipient patients of fetal nigral transplants provided a prion-like cell-to-cell transmission hypothesis for abnormal αSyn. The extracellular αSyn fibrils can internalize to the cells and enhance intracellular formation of protein inclusions, thereby reducing cell viability. These findings suggest that effective removal of abnormal species of αSyn in the extracellular space as well as intracellular compartments can be of therapeutic relevance. In this review, we will focus on αSyn-triggered neuronal cell death and provide possible disease-modifying therapies targeting abnormally accumulating αSyn.     

Cannabinoid Effects on β Amyloid Fibril and Aggregate Formation,Neuronal and Microglial-Activated Neurotoxicity In Vitro

Cannabinoid (CB) ligands have demonstrated neuroprotective properties. In this study we compared the effects of a diverse set of CB ligands against β amyloid-mediated neuronal toxicity and activated microglial-conditioned media-based neurotoxicity in vitro, and compared this with a capacity to directly alter β amyloid (Aβ) fibril or aggregate formation. Neuroblastoma (SH-SY5Y) cells were exposed to Aβ_1–42 directly or microglial (BV-2 cells) conditioned media activated with lipopolysaccharide (LPS) in the presence of the CB1 receptor-selective agonist ACEA, CB2 receptor-selective agonist JWH-015, phytocannabinoids Δ⁹-THC and cannabidiol (CBD), the endocannabinoids 2-arachidonoyl glycerol (2-AG) and anandamide or putative GPR18/GPR55 ligands O-1602 and abnormal-cannabidiol (Abn-CBD). TNF-α and nitrite production was measured in BV-2 cells to compare activation via LPS or albumin with Aβ_1–42. Aβ_1–42 evoked a concentration-dependent loss of cell viability in SH-SY5Y cells but negligible TNF-α and nitrite production in BV-2 cells compared to albumin or LPS. Both albumin and LPS-activated BV-2 conditioned media significantly reduced neuronal cell viability but were directly innocuous to SH-SY5Y cells. Of those CB ligands tested, only 2-AG and CBD were directly protective against Aβ-evoked SH-SY5Y cell viability, whereas JWH-015, THC, CBD, Abn-CBD and O-1602 all protected SH-SY5Y cells from BV-2 conditioned media activated via LPS. While CB ligands variably altered the morphology of Aβ fibrils and aggregates, there was no clear correlation between effects on Aβ morphology and neuroprotective actions. These findings indicate a neuroprotective action of CB ligands via actions at microglial and neuronal cells.     

Neuronal cholecystokinin,gastrin-releasing peptide,neurotensin, and β-endorphin in the intestine of the guinea pig

Summary The guinea-pig intestine was found to harbor nerve fibers containing immunoreactive cholecystokinin (CCK), gastrin-releasing peptide (GRP), neurotensin or - endorphin. Such fibers occurred in the myenteric and submucous ganglia and in the smooth muscle. GRP- and CCK-fibers, in addition, were found in the mucosa. Following colchicine treatment, neuronal perikarya in the myenteric ganglia displayed CCK-, GRP-, or -endorphin immunoreactivity. CCK-immunoreactive perikarya were located also in the submucous ganglia. Neurotensin-immunoreactive cell bodies could not be detected. The presence of immunoreactive neuronal perikarya in intramural ganglia indicates that CCK-, GRP- and -endorphin-containing fibers are intrinsic to the gut wall. GRP, neurotensin, and -endorphin were identified in extracts of smooth muscle by immunochemical and Chromatographic analysis.CCK-8, GRP and neurotensin contracted the isolated taenia coli. Tetrodotoxin reduced the response to CCK-8 but not that to GRP and neurotensin, suggesting that the two latter peptides act directly on smooth muscle receptors. The effect of CCK-8 is partly mediated by cholinergic nerves, since not only tetrodotoxin but also atropine greatly reduced the CCK-8-induced contractile response. The substance P (SP) antagonist, (d-Pro², d-Trp^7,9)-SP_1–11 had no effect on the CCK-8-induced contraction of the taenia. CCK-8 enhanced the SP-mediated (atropine-resistant) contractile response to electrical stimulation but not that mediated by acetylcholine. -Endorphin had no effect on the tension of the muscle but reduced the response to electrical stimulation (cholinergic as well as SP-mediated) through a naloxone-sensitive mechanism.While CCK-8 and -endorphin seem to play neuromodulatory roles in the taenia coli, the significance of GRP and neurotensin remains enigmatic.     

Delayed Administration of Parecoxib, a Specific COX-2 Inhibitor, Attenuated Postischemic Neuronal Apoptosis by Phosphorylation Akt and GSK-3β

Parecoxib is a recently described novel COX-2 inhibitor whose functional significance and neuroprotective mechanisms remain elusive. Therefore, in this study, we aimed to investigate whether delayed administration of parecoxib inhibited mitochondria-mediated neuronal apoptosis induced by ischemic reperfusion injury via phosphorylating Akt and its downstream target protein, glycogen synthase kinase 3β (GSK-3β). Adult male Sprague–Dawley rats were administered parecoxib (10 or 30 mg kg⁻¹, IP) or isotonic saline twice a day starting 24 h after middle cerebral artery occlusion (MCAO) for three consecutive days. Cerebral infarct volume, apoptotic neuron, caspase-3 immunoreactivity and the protein expression of p-Akt, p-GSK-3β and Cytochrome C in cerebral ischemic cortex were evaluated at 96 h after reperfusion. Parecoxib significantly diminished infarct volume and attenuated neuron apoptosis in a dose-independent manner, compared with MCAO group alone. Increased p-Akt and p-GSK-3β was observed in the ischemic penumbra of parecoxib group after stroke. Moreover, parecoxib also reduced the release of Cytochrome C from mitochondrial into cytosol and attenuated the caspase-3 immunoreactivity in the penumbra. Taken together, these results suggested that parecoxib ameliorated postischemic mitochondria-mediated neuronal apoptosis induced by focal cerebral ischemia in rats and this neuroprotective potential is involved in phosphorylation of Akt and GSK-3β.     

��-Amyloid1�C42 Gene Transfer Model Exhibits Intraneuronal Amyloid, Gliosis, Tau Phosphorylation, and Neuronal Loss

Alzheimer disease is characterized by extracellular β-amyloid (Aβ) plaques and intracellular inclusions containing neurofibrillary tangles of phospho-Tau and intraneuronal Aβ associated with neuronal cell death. We generated a novel gene transfer animal model using lentiviral Aβ_1–42 that resulted in intracellular but not extracellular Aβ accumulations in the targeted rat primary motor cortex. Expression of intracellular Aβ_1–42 led to pathological changes seen in human Alzheimer disease brains, including cell death, inflammatory signs, activation of two Tau kinases, and Tau hyperphosphorylation. Promoting clearance of lentiviral Aβ_1–42 reversed these effects, demonstrating that intraneuronal Aβ_1–42 is a toxic peptide that lies upstream of Tau modification. These studies reveal the role of intracellular Aβ_1–42 in a novel gene transfer animal model, which is a useful tool to study intraneuronal Aβ_1–42-induced pathology in the absence of extracellular plaques. Targeted delivery of Aβ will allow speedy delineation of pathological mechanisms associated with specific neurodegenerative lesions.     

SMN, Gemin2 and Gemin3 Associate with β-Actin mRNA in the Cytoplasm of Neuronal Cells In Vitro

Childhood spinal muscular atrophy is caused by a reduced expression of the survival motor neuron (SMN) protein. SMN has been implicated in the axonal transport of β-actin mRNA in both primary and transformed neuronal cell lines, and loss of this function could account, at least in part, for spinal muscular atrophy onset and pathological specificity. Here we have utilised a targeted screen to identify mRNA associated with SMN, Gemin2 and Gemin3 in the cytoplasm of a human neuroblastoma cell line, SHSY5Y. Importantly, we have provided the first direct evidence that β-actin mRNA is present in SMN cytoplasmic complexes in SHSY5Y cells.     

Nonlinear Decoding and Asymmetric Representation of Neuronal Input Information by CaMKIIα and Calcineurin

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Predictive Coding or Evidence Accumulation? False Inference and Neuronal Fluctuations

Perceptual decisions can be made when sensory input affords an inference about what generated that input. Here, we report findings from two independent perceptual experiments conducted during functional magnetic resonance imaging (fMRI) with a sparse event-related design. The first experiment, in the visual modality, involved forced-choice discrimination of coherence in random dot kinematograms that contained either subliminal or periliminal motion coherence. The second experiment, in the auditory domain, involved free response detection of (non-semantic) near-threshold acoustic stimuli. We analysed fluctuations in ongoing neural activity, as indexed by fMRI, and found that neuronal activity in sensory areas (extrastriate visual and early auditory cortex) biases perceptual decisions towards correct inference and not towards a specific percept. Hits (detection of near-threshold stimuli) were preceded by significantly higher activity than both misses of identical stimuli or false alarms, in which percepts arise in the absence of appropriate sensory input. In accord with predictive coding models and the free-energy principle, this observation suggests that cortical activity in sensory brain areas reflects the precision of prediction errors and not just the sensory evidence or prediction errors per se.     

Can Power-Law Scaling and Neuronal Avalanches Arise from Stochastic Dynamics?

The presence of self-organized criticality in biology is often evidenced by a power-law scaling of event size distributions, which can be measured by linear regression on logarithmic axes. We show here that such a procedure does not necessarily mean that the system exhibits self-organized criticality. We first provide an analysis of multisite local field potential (LFP) recordings of brain activity and show that event size distributions defined as negative LFP peaks can be close to power-law distributions. However, this result is not robust to change in detection threshold, or when tested using more rigorous statistical analyses such as the Kolmogorov–Smirnov test. Similar power-law scaling is observed for surrogate signals, suggesting that power-law scaling may be a generic property of thresholded stochastic processes. We next investigate this problem analytically, and show that, indeed, stochastic processes can produce spurious power-law scaling without the presence of underlying self-organized criticality. However, this power-law is only apparent in logarithmic representations, and does not survive more rigorous analysis such as the Kolmogorov–Smirnov test. The same analysis was also performed on an artificial network known to display self-organized criticality. In this case, both the graphical representations and the rigorous statistical analysis reveal with no ambiguity that the avalanche size is distributed as a power-law. We conclude that logarithmic representations can lead to spurious power-law scaling induced by the stochastic nature of the phenomenon. This apparent power-law scaling does not constitute a proof of self-organized criticality, which should be demonstrated by more stringent statistical tests.     

Protection of PMS777, a New AChE Inhibitor with PAF Antagonism, Against Amyloid-β-Induced Neuronal Apoptosis and Neuroinflammation

Amyloid-β (Aβ) plays a central role in the neuroinflammation and cholinergic neuronal apoptosis in Alzheimer’s disease, and thus has been considered as a main determinant of this disease. In the previous study, we reported that PMS777, a novel bis-interacting ligand for acetylcholinesterase (AChE) inhibition and platelet-activating factor (PAF) receptor antagonism, could significantly attenuate PAF-induced neurotoxicity. Continuing our efforts, we further investigated the protective effect of PMS777 on Aβ-induced neuronal apoptosis in vitro and neuroinflammation in vivo. PMS777 (1–100 μM) was found to inhibit Aβ-induced human neuroblastoma SH-SY5Y cell apoptosis in a concentration-dependent manner. Concurrently, PMS777 increased ratio of bcl-2 to bax mRNA, and inhibited both mRNA expression and activity of caspase-3 in SH-SY5Y cells after the exposure with Aβ. In vivo experimental study demonstrated that PMS777 could attenuate Aβ-induced microglial and astrocytic activation in the rat hippocampus after systemic administration. These results suggest that PMS777 potently protects against Aβ-induced neuronal apoptosis and neuroinflammation, and warrants further investigations in connection with its potential value in the treatment of Alzheimer’s disease. The authors Juan Li and Jinjia Hu contributed equally to this article.     

Is There a Molecular Logic That Sustains Neuronal Functional Integrity and Survival? Lipid Signaling Is Necessary for Neuroprotective Neuronal Transcriptional Programs

A challenge to civilization is the growing incidence in the loss of sight and cognition due to increased life expectancy. Therefore, we are confronted with a rise in the occurrence of photoreceptor- and neuronal-survival failure, as reflected mainly by age-related macular degeneration (AMD) and Alzheimer’s disease (AD). Nervous system development is driven by neuronal apoptotic cell death, and thereafter, for the entire lifespan of an organism, neurons are postmitotic cells. In neurodegenerative diseases, apoptosis and other forms of cells death lead to selective neuronal loss. Although age is the main risk factor, not everyone develops these diseases during aging. Despite decades of important findings about neuronal cell death, the specific mechanisms that regulate neuronal survival remain incompletely understood.     

κ-Casein-Based Hierarchical Suprastructures and Their Use for Selective Temporal and Spatial Control over Neuronal Differentiation

Functions are diversified by producing hierarchical structures from a single raw material. Biologically compatible milk protein of κ-casein has been employed to fabricate higher-order suprastructures. In the presence of dithiothreitol and heat treatment, κ-casein transforms into amyloid fibrils with distinctive morphology attributable to mechanism-based fibrillar polymorphism. As the fibrils elongate to yield high aspect ratio during high-temperature incubation, the resulting fibrils laterally associate into the liquid crystalline state by forming a two-dimensional fibrillar array. Following a desalting process, the fibrillar arrays turn into a three-dimensional matrix of hydrogel that could be selectively disintegrated by subsequent salt treatment. The hydrogel was demonstrated to be a matrix capable of exhibiting controlled release of bioactive substances like retinoic acid, which led to temporal and spatial control over the differentiation of neuronal cells. Therefore, the hierarchical suprastructure formation derived from the single protein of κ-casein producing one-dimensional protein nanofibrils, a two-dimensional liquid crystalline state and a three-dimensional hydrogel could be widely appreciated in various areas of nanobiotechnology including drug delivery and tissue engineering.     

Time-Warp–Invariant Neuronal Processing

Fluctuations in the temporal durations of sensory signals constitute a major source of variability within natural stimulus ensembles. The neuronal mechanisms through which sensory systems can stabilize perception against such fluctuations are largely unknown. An intriguing instantiation of such robustness occurs in human speech perception, which relies critically on temporal acoustic cues that are embedded in signals with highly variable duration. Across different instances of natural speech, auditory cues can undergo temporal warping that ranges from 2-fold compression to 2-fold dilation without significant perceptual impairment. Here, we report that time-warp–invariant neuronal processing can be subserved by the shunting action of synaptic conductances that automatically rescales the effective integration time of postsynaptic neurons. We propose a novel spike-based learning rule for synaptic conductances that adjusts the degree of synaptic shunting to the temporal processing requirements of a given task. Applying this general biophysical mechanism to the example of speech processing, we propose a neuronal network model for time-warp–invariant word discrimination and demonstrate its excellent performance on a standard benchmark speech-recognition task. Our results demonstrate the important functional role of synaptic conductances in spike-based neuronal information processing and learning. The biophysics of temporal integration at neuronal membranes can endow sensory pathways with powerful time-warp–invariant computational capabilities.     

Menstrual-PGF2α, PGE2 and TXA2 in normal and dysmenorrheic women and their temporal relationship to dysmenorrhea

Although it has been demonstrated that primary dysmenorrhea is associated with elevated levels of PGF_2α in the menstrual fluid, little is actually known of the menstrual-PG profiles of either dysmenorrheic or normal women. In this study, menstrual fluid from normal and dysmenorrheic women was collected from tampons and extracted for PG-like substances. The PGF_2α, PGE₂ and TXA₂ content was analyzed by RIA.This study demonstrates that dysmenorrheics have significantly higher levels/concentrations of menstrual-PGF_2α and PGe₂ than do normal women, and that there is no difference in the menstrual-PGF_2α: PGE₂ ratio between the two groups. Also, there is no significant difference in the amount/concentration of menstrual-thromboxane between dysmenorrheic and normal women. Of the parameters considered, the levels/-concentrations of menstrual-PGF_2α, PGE₂ and TXA₂, dysmenorrheic pain correlates best with the rate of menstrual-PGF_2α release.     

Neuronal cell adhesion genes: Key players in risk for schizophrenia,bipolar disorder and other neurodevelopmental brain disorders?

The major mental disorders, schizophrenia and bipolar disorder, are substantially heritable. Recent genomic studies have identified a small number of common and rare risk genes contributing to both disorders and support epidemiological evidence that genetic susceptibility overlaps between them. Prompted by the question of whether risk genes cluster in specific molecular pathways or implicate discrete mechanisms, we and others have developed hypothesis-free methods of investigating genome-wide association datasets at a pathway-level. The application of our method to the 212 experimentally-derived pathways in the Kyoto Encyclopedia of Genes and Genomes (KEGG) database identified significant association between the cell adhesion molecule (CAM) pathway and both schizophrenia and bipolar disorder susceptibility across three GWAS datasets. Interestingly, a similar approach applied to an autistic spectrum disorders (ASDs) sample identified a similar pathway and involved many of the same genes. Disruption of a number of these genes (including NRXN1, CNTNAP2 and CASK) are known to cause diverse neurodevelopmental brain disorder phenotypes including schizophenia, autism, learning disability and specific language disorder. Taken together these studies bring the CAM pathway sharply into focus for more comprehensive DNA sequencing to identify the critical genes, and investigate their relationships and interaction with environmental risk factors in the expression of many seemingly different neurodevelopmental disorders.Key words: schizophrenia, bipolar disorder, genome-wide association, molecular pathway analysis, cell adhesion molecules, neurexin-1Taken together the major mental disorders, schizophrenia and bipolar disorder, affect almost 2% of the adult population and are a major cause of global disability. In the absence of a clear understanding of the pathophysiological processes involved, diagnosis is based on a clinical assessment of symptoms (e.g., delusions, hallucinations, depression and mania) and course of illness. Modern treatments, which emerged in the mid-twentieth century, although efficacious for many, were discovered serendipitously and are far from perfect as both disorders are still associated with substantial morbidity and premature mortality. The statistics are sobering: people with severe mental illness die on average 25 years earlier than those in the general population. Intensive investigation of known mood stabilizers (e.g., lithium) and antipsychotic medications (e.g., haloperidol and clozapine) has yet to translate into better understanding of aetiology or a breakthrough in development of new therapies leading to improved outcome.What unites these disorders is that they are substantially heritable.¹ The emergence of molecular genetics offered the exciting possibility of identifying the causative genes as a key to understanding the biology involved. As has been the case with most complex genetic disorders, progress has been slow but has gathered pace as our ability to investigate the genome has improved and collaborative efforts have generated large sample sizes. Within five years we have advanced from looking through a narrow aperture at hundreds of polymorphic markers, in a selected region or widely scattered across the chromosomes in studies involving hundreds of individuals, to being able to examine most common genomic variation (>85%), captured by a million genetic markers in large-scale studies of thousands of patients. A number of common risk variants, albeit of small effect, have emerged from genome-wide association studies (GWAS) in schizophrenia and bipolar disorder, respectively.^2–6 Some genes (e.g., ZNF804A,² CACNA1C⁶) have been implicated in both disorders and there may be many more. Indeed, the genetic architecture of these disorders may include a substantial polygenic component involving thousands of common alleles of very small effect, many of which increase susceptibility to both schizophrenia and bipolar disorder.³ The bad news is that confirming such small effects may not be feasible even with very large sample sizes (n>100,000 patients). Having only a partial picture of the genes involved is likely to be a substantial barrier to translational research.What is more biologically informative than linking a gene or chromosomal region to a disorder is knowing if these small effects are concentrated in genes relating to a specific mechanism or implicating specific molecular pathways. Many groups have been developing pathway-based approaches to analyzing genome-wide association datasets and our SNP-ratio test (SRT) is just one such approach.^7–13 The SRT can be applied flexibly to different pathway resources as a hypothesis-free test, which simply identifies whether there are more nominally significant SNPs in genes mapping to that pathway in cases in a GWAS dataset than to genes mapping to all other indicated pathways.⁷ Applying this approach to the Kyoto Encyclopedia of Genes and Genomes (KEGG) database of 212 experimentally-derived pathways we captured information on 4,760 genes.¹⁴ We performed a discovery analysis in the International Schizophrenia Consortium dataset, with nominally significant pathways being replicated in an independent, large schizophrenia GWAS dataset.^4,5 Pathways with confirmed association were then tested in a bipolar disorder GWAS dataset to investigate overlap between these conditions.¹⁵ The first step analysis identified 47 nominally significant pathways of which five were associated in the independent schizophrenia dataset. Of these five, only the cell adhesion molecule (CAM) pathway (hsa04514) (p = 0.001) exceeded a conservative testing for multiple testing. Of note, one of the other five identified pathways, the ‘Tight Junction’ pathway (hsa045130) overlaps with the CAM pathway at a molecular level and is involved in many of the same functions. In all, 28 CAM genes of 110 contributing to the analysis had significantly associated SNPs in both schizophrenia datasets and 14 SNPs across 6 CAM genes (NRXN1, CDH4, GLG1, HLA-DQA2, CNTN1 and PDCD1LG2) shared the same risk alleles (see Fig. 1). Association at a pathway-level was confirmed with bipolar disorder although only approximately half of the genes implicated in the discovery analysis showed evidence of association in the bipolar disorder dataset. Further work is required in additional samples to investigate whether this difference represents a lower total burden of contributory risk variants in bipolar disorder (a less severe phenotype) or whether different genes or mechanisms within the pathway may explain phenotypic differences between the disorders.Open in a separate windowFigure 1Genes involved in KEGG Cell Adhesion Molecules pathway (www.genome.jp/dbget-bin/www_bget?pathway+hsa04514) Color scheme: red, significant SNPs in gene in both ISC and GAIN datasets; red with emboldened border and gene name, replication of significant SNPs* in gene in ISC and GAIN datasets; orange, significant SNPs in gene in ISC dataset only; yellow, significant SNPs in gene in GAIN dataset only; grey, no significantly associated SNPs in gene for either dataset/No. SNPs in gene tested/Gene not included in SRT *Replication = same risk allele associated with SZ in the two datasets.That cell adhesion molecules (CAMs) would be implicated in the aetiology of schizophrenia and bipolar disorder is hardly surprising. There is strong evidence, particularly for schizophrenia, to support a neurodevelopmental contribution to aetiology and known (albeit weak) environmental risk factors include maternal starvation, infection and birth trauma (reviewed in ref. ¹⁶). There is growing support, including from neuropathological studies, to suggest that psychosis may be a disorder that involves aberrant brain wiring or dysconnectivity (reviewed in ref. ¹⁷). Cell adhesion molecules have an important role in brain development including in axonal/dendrite growth, synapse formation and plasticity. Neuronal CAMs are also known to have an important role in neurotransmission, including at glutamatergic and GABAergic synapses, which have been implicated in schizophrenia.¹⁸So what can we learn from the 28 CAM genes contributing to the pathway-level association in our analysis? The individual effect sizes at each gene involved are small. Taking stock of evidence from other common disorders (e.g., type 2 diabetes) these early findings are unlikely to be helpful for risk prediction or diagnosis.¹⁹ Their principle utility may be in understanding the aetiology of schizophrenia, bipolar disorder and possibly other neurodevelopmental brain disorders. So what do we know about these genes? Many of the genes involved in this pathway have been implicated in neuropsychiatric disorders or other brain phenotypes.²⁰ For example, this is the case for two of the five genes where SNPs directly replicate across GWAS samples. The sixth gene, HLA-DQA2 maps to the major histocompatibility complex (MHC) region on chromosome 6p, which has been implicated in neuronal plasticity, but presents challenges for genetic mapping.²¹ Disruption of the NRXN1 gene has been reported in both schizophrenia and autism cases or families (see below). Axonal neurexins form transmembrane complexes with neuroligins on dendrites and are required for the formation of synaptic contacts and for efficient neurotransmission-including maintaining postsynaptic NMDA receptor function. The gene is a direct interactor of the cytoskeleton membrane scaffolding protein gene CASK (OMIM:300171), which is associated in both schizophrenia samples in our study, but is assigned to the “Tight Junction” pathway in KEGG. CASK may have a role in synaptic plasticity by coupling synaptic vesicle exocytosis to neuronal cell adhesion.²² CDH4 is a classical cadherin thought to be involved in brain segmentation and neuronal outgrowth. This locus has not received particular support from prior linkage or association studies, but curiously association between a SNP at this gene and total cerebral brain volume was the only genome-wide significant finding to emerge from a GWAS study of brain aging using MRI and cognitive assessment of 705 healthy participants from the Framingham study.²³ Reduced brain volumes are a recognized feature of schizophrenia and this may point to a role in maintenance rather than formation of neuronal connections.Several other recent genomic studies have provided additional support for involvement of CAMs in both bipolar disorder and autistic spectrum disorders (ASDs). A recent GWAS study in bipolar disorder and subsequent replication efforts have provided some support for association with CDH7.²⁴ A GWAS study in ASDs identified association with the chromosome 5p14.1 region containing other members of the cadherin superfamily, CDH 9 and CDH 10.²⁵ Wang and colleagues went further and in a strategy not dissimilar to our approach applied two pathway-based association analyses to their genotype data. In the first they identified that a group of 25 cadherin genes showed more significant association with ASDs than all other genes (p = 0.02), a signal that was enriched by including eight neurexin family genes (p = 0.004). The result was confirmed using a second formal pathway-association method.²⁵ Although the methodologies differed, the genes NRXN1, CNTNAP2 and CDH4 were common to the risk pathways identified across the ASDs by Wang and colleagues in their study and in our investigation of schizophrenia and bipolar disorder.These findings add to growing molecular evidence for overlap between childhood-onset neurodevelopmental disorders (e.g., ASDs) and disorders of typical onset in adolescence or early adulthood like schizophrenia and bipolar disorder (reviewed in ref. ²⁶). The studies performed by our group and Wang and colleagues only investigated common SNP variation and there is increasing realization of the potential importance of rare, highly penetrant structural variation in the aetiology of neurodevelopmental brain disorders. A number of microdeletion/microduplication syndromes have been identified that are associated with ASDs, schizophrenia, intellectual disability, specific language delay and other neurodevelopmental phenotypes (reviewed in ref. ²⁷). Many of these disrupt genes involved in CAM pathways. For instance, disruption of NRXN1 has been reported in cases of both autism and schizophrenia; CASK deletions are reported in individuals with learning disability and brain malformation phenotypes; and disruption of CNTNAP2 has been reported in autism, language disorder and schizophrenia. Taking NRXN1 specifically, many of its post-synaptic binding partners (the neuroligins) and their postsynaptic density interactors (e.g., SHANK3) have been identified as rare causes of ASDs (reviewed in ref. ²⁸).Together these studies raise the possibility that susceptibility to ASDs and psychotic disorders may involve overlapping molecular aetiology where an accumulation of small effects from many common genetic risk variants or more highly penetrant mutations induce neuronal dysconnectivity by disrupting CAM function. This raises exciting new avenues for research into the mechanisms and processes involved. The next key step may be large-scale DNA sequencing of these genes and their interactors to identify whether smaller structural or point mutations, undetectable in the current studies, also contribute to risk. By neccessity these studies will require detailed phenotypic information and encompass different phenotypes to explore how genetic risk is expressed as seemingly different neurodevelopmental endophenotypes. This can inform functional studies and identification of potential therapeutic targets. Finally, although the common risk genes identified by our analysis are of limited clinical utility, more highly penetrant mutations although individually rare may be diagnostically significant across these neurodevelopmental disorders as is already being realised in ASDs.²⁹