Genetic and morphological features of human iPSC-derived neurons with chromosome 15q11.2 (BP1-BP2) deletions

Current advancements of modelling schizophrenia using patient-derived induced pluripotent stem cells

Schizophrenia (SZ) is a severe psychiatric disorder, with a prevalence of 1-2% world-wide and substantial health- and social care costs. The pathology is influenced by both genetic and environmental factors, however the underlying cause still remains elusive. SZ has symptoms including delusions, hallucinations, confused thoughts, diminished emotional responses, social withdrawal and anhedonia. The onset of psychosis is usually in late adolescence or early adulthood. Multiple genome-wide association and whole exome sequencing studies have provided extraordinary insights into the genetic variants underlying familial as well as polygenic forms of the disease. Nonetheless, a major limitation in schizophrenia research remains the lack of clinically relevant animal models, which in turn hampers the development of novel effective therapies for the patients. The emergence of human induced pluripotent stem cell (hiPSC) technology has allowed researchers to work with SZ patient-derived neuronal and glial cell types in vitro and to investigate the molecular basis of the disorder in a human neuronal context. In this review, we summarise findings from available studies using hiPSC-based neural models and discuss how these have provided new insights into molecular and cellular pathways of SZ. Further, we highlight different examples of how these models have shown alterations in neurogenesis, neuronal maturation, neuronal connectivity and synaptic impairment as well as mitochondrial dysfunction and dysregulation of miRNAs in SZ patient-derived cultures compared to controls. We discuss the pros and cons of these models and describe the potential of using such models for deciphering the contribution of specific human neural cell types to the development of the disease.

Passage number affects differentiation of sensory neurons from human induced pluripotent stem cells

Induced pluripotent stem cells (iPSCs) are a valuable resource for neurological disease-modeling and drug discovery due to their ability to differentiate into neurons reflecting the genetics of the patient from which they are derived. iPSC-derived cultures, however, are highly variable due to heterogeneity in culture conditions. We investigated the effect of passage number on iPSC differentiation to optimize the generation of sensory neurons (iPSC-dSNs). Three iPSC lines reprogrammed from the peripheral blood of three donors were differentiated into iPSC-dSNs at passage numbers within each of the following ranges: low (5-10), intermediate (20-26), and high (30-38). Morphology and pluripotency of the parent iPSCs were assessed prior to differentiation. iPSC-dSNs were evaluated based on electrophysiological properties and expression of key neuronal markers. All iPSC lines displayed similar morphology and were similarly pluripotent across passage numbers. However, the expression levels of neuronal markers and sodium channel function analyses indicated that iPSC-dSNs differentiated from low passage numbers better recapitulated the sensory neuron phenotype than those differentiated from intermediate or high passage numbers. Our results demonstrate that lower passage numbers may be better suited for differentiation into peripheral sensory neurons.

Modeling schizophrenia with iPS cell technology and disease mouse models

Induced pluripotent stem cell (iPSC) technology, which enables the direct analysis of neuronal cells with the same genetic background as patients, has recently garnered significant attention in schizophrenia research. This technology is important because it enables a comprehensive interpretation using mice and human clinical research and cross-species verification. Here I review recent advances in modeling schizophrenia using iPSC technology, alongside the utility of disease mouse models.

Induced pluripotent stem cells for 2D and 3D modelling the biological basis of schizophrenia and screening possible therapeutics

Induced pluripotent stem cells (iPSCs) are providing unprecedented insight into complex neuropsychiatric disorders such as schizophrenia (SZ). Here we review the use of iPSCs for investigating the etiopathology and treatment of SZ, beginning with conventional in vitro two-dimensional (2D; monolayer) cell modelling, through to more advanced 3D tissue studies. With the advent of 3D modelling, utilising advanced differentiation paradigms and additive manufacturing technologies, inclusive of patient-specific cerebral/neural organoids and bioprinted neural tissues, such live disease-relevant tissue systems better recapitulate "within-body" tissue function and pathobiology. We posit that by enabling better understanding of biological causality, these evolving strategies will yield novel therapeutic targets and accordingly, drug candidates.

FMRP and CYFIP1 at the Synapse and Their Role in Psychiatric Vulnerability

There is increasing awareness of the role genetic risk variants have in mediating vulnerability to psychiatric disorders such as schizophrenia and autism. Many of these risk variants encode synaptic proteins, influencing biological pathways of the postsynaptic density and, ultimately, synaptic plasticity. Fragile-X mental retardation 1 (FMR1) and cytoplasmic fragile-X mental retardation protein (FMRP)-interacting protein 1 (CYFIP1) contain 2 such examples of highly penetrant risk variants and encode synaptic proteins with shared functional significance. In this review, we discuss the biological actions of FMRP and CYFIP1, including their regulation of (i) protein synthesis and specifically FMRP targets, (ii) dendritic and spine morphology, and (iii) forms of synaptic plasticity such as long-term depression. We draw upon a range of preclinical studies that have used genetic dosage models of FMR1 and CYFIP1 to determine their biological function. In parallel, we discuss how clinical studies of fragile X syndrome or 15q11.2 deletion patients have informed our understanding of FMRP and CYFIP1, and highlight the latest psychiatric genomic findings that continue to implicate FMRP and CYFIP1. Lastly, we assess the current limitations in our understanding of FMRP and CYFIP1 biology and how they must be addressed before mechanism-led therapeutic strategies can be developed for psychiatric disorders.

Negative Symptoms of Schizophrenia and Dopaminergic Transmission: Translational Models and Perspectives Opened by iPSC Techniques

Negative symptoms (NS) represent a heterogeneous dimension of schizophrenia (SCZ), associated with a poor functional outcome. A dysregulated dopamine (DA) system, including a reduced D1 receptor activation in the prefrontal cortex, DA hypoactivity in the caudate and alterations in D3 receptor activity, seems to contribute to the pathogenesis of NS. However, failure to take into account the NS heterogeneity has slowed down progress in research on their neurobiological correlates and discoveries of new effective treatments. A better neurobiological characterization of NS is needed, and this requires objective quantification of their features that can be applied in translational models, such as animal models and human inducible pluripotent stem cells (iPSC). In this review we summarize the evidence for dopaminergic alterations relevant to NS in translational animal models focusing on dysfunctional motivation, a core aspect of NS. Among others, experiments on mutant rodents with an overexpression of DA D2 or D3 receptors and the dopamine deficient mice are discussed. In the second part we summarize the findings from recent studies using iPSC to model the pathogenesis of SCZ. By retaining the genetic background of risk genetic variants, iPSC offer the possibility to study the effect of de novo mutations or inherited polymorphisms from subgroups of patients and their response to drugs, adding an important tool for personalized psychiatry. Given the key role of DA in NS, we focus on findings of iPSC-derived DA neurons. Since implementation of iPSC-derived neurons to study the neurobiology of SCZ is a relatively recent acquisition, the available data are limited. We highlight some methodological aspects of relevance in the interpretation of in vitro testing results, including limitations and strengths, offering a critical viewpoint for the implementation of future pharmacological studies aimed to the discovery and characterization of novel treatments for NS.

The sociability spectrum: evidence from reciprocal genetic copy number variations

Sociability entails some of the most complex behaviors processed by the central nervous system. It includes the detection, integration, and interpretation of social cues and elaboration of context-specific responses that are quintessentially species-specific. There is an ever-growing accumulation of molecular associations to autism spectrum disorders (ASD), from causative genes to endophenotypes across multiple functional layers; these however, have rarely been put in context with the opposite manifestation featured in hypersociability syndromes. Genetic copy number variations (CNVs) allow to investigate the relationships between gene dosage and its corresponding phenotypes. In particular, CNVs of the 7q11.23 locus, which manifest diametrically opposite social behaviors, offer a privileged window to look into the molecular substrates underlying the developmental trajectories of the social brain. As by definition sociability is studied in humans postnatally, the developmental fluctuations causing social impairments have thus far remained a black box. Here, we review key evidence of molecular players involved at both ends of the sociability spectrum, focusing on genetic and functional associations of neuroendocrine regulators and synaptic transmission pathways. We then proceed to propose the existence of a molecular axis centered around the paradigmatic dosage imbalances at the 7q11.23 locus, regulating networks responsible for the development of social behavior in humans and highlight the key role that neurodevelopmental models from reprogrammed pluripotent cells will play for its understanding.

Copy number variants (CNVs): a powerful tool for iPSC-based modelling of ASD

Patients diagnosed with chromosome microdeletions or duplications, known as copy number variants (CNVs), present a unique opportunity to investigate the relationship between patient genotype and cell phenotype. CNVs have high genetic penetrance and give a good correlation between gene locus and patient clinical phenotype. This is especially effective for the study of patients with neurodevelopmental disorders (NDD), including those falling within the autism spectrum disorders (ASD). A key question is whether this correlation between genetics and clinical presentation at the level of the patient can be translated to the cell phenotypes arising from the neurodevelopment of patient induced pluripotent stem cells (iPSCs).Here, we examine how iPSCs derived from ASD patients with an associated CNV inform our understanding of the genetic and biological mechanisms underlying the aetiology of ASD. We consider selection of genetically characterised patient iPSCs; use of appropriate control lines; aspects of human neurocellular biology that can capture in vitro the patient clinical phenotype; and current limitations of patient iPSC-based studies. Finally, we consider how future research may be enhanced to maximise the utility of CNV patients for research of pathological mechanisms or therapeutic targets.

Dysregulation of protein synthesis and dendritic spine morphogenesis in ASD: studies in human pluripotent stem cells

Autism spectrum disorder (ASD) is a brain disorder that involves changes in neuronal connections. Abnormal morphology of dendritic spines on postsynaptic neurons has been observed in ASD patients and transgenic mice that model different monogenetic causes of ASD. A number of ASD-associated genetic variants are known to disrupt dendritic local protein synthesis, which is essential for spine morphogenesis, synaptic transmission, and plasticity. Most of our understanding on the molecular mechanism underlying ASD depends on studies using rodents. However, recent advance in human pluripotent stem cells and their neural differentiation provides a powerful alternative tool to understand the cellular aspects of human neurological disorders. In this review, we summarize recent progress on studying mRNA targeting and local protein synthesis in stem cell-derived neurons, and discuss how perturbation of these processes may impact synapse development and functions that are relevant to cognitive deficits in ASD.

Mental health dished up-the use of iPSC models in neuropsychiatric research

Genetic and molecular mechanisms that play a causal role in mental illnesses are challenging to elucidate, particularly as there is a lack of relevant in vitro and in vivo models. However, the advent of induced pluripotent stem cell (iPSC) technology has provided researchers with a novel toolbox. We conducted a systematic review using the PRISMA statement. A PubMed and Web of Science online search was performed (studies published between 2006–2020) using the following search strategy: hiPSC OR iPSC OR iPS OR stem cells AND schizophrenia disorder OR personality disorder OR antisocial personality disorder OR psychopathy OR bipolar disorder OR major depressive disorder OR obsessive compulsive disorder OR anxiety disorder OR substance use disorder OR alcohol use disorder OR nicotine use disorder OR opioid use disorder OR eating disorder OR anorexia nervosa OR attention-deficit/hyperactivity disorder OR gaming disorder. Using the above search criteria, a total of 3515 studies were found. After screening, a final total of 56 studies were deemed eligible for inclusion in our study. Using iPSC technology, psychiatric disease can be studied in the context of a patient’s own unique genetic background. This has allowed great strides to be made into uncovering the etiology of psychiatric disease, as well as providing a unique paradigm for drug testing. However, there is a lack of data for certain psychiatric disorders and several limitations to present iPSC-based studies, leading us to discuss how this field may progress in the next years to increase its utility in the battle to understand psychiatric disease.

The 15q11.2 BP1-BP2 Microdeletion (Burnside-Butler) Syndrome: In Silico Analyses of the Four Coding Genes Reveal Functional Associations with Neurodevelopmental Phenotypes

The 15q11.2 BP1-BP2 microdeletion (Burnside–Butler) syndrome is emerging as the most frequent pathogenic copy number variation (CNV) in humans associated with neurodevelopmental disorders with changes in brain morphology, behavior, and cognition. In this study, we explored functions and interactions of the four protein-coding genes in this region, namely NIPA1, NIPA2, CYFIP1, and TUBGCP5, and elucidate their role, in solo and in concert, in the causation of neurodevelopmental disorders. First, we investigated the STRING protein-protein interactions encompassing all four genes and ascertained their predicted Gene Ontology (GO) functions, such as biological processes involved in their interactions, pathways and molecular functions. These include magnesium ion transport molecular function, regulation of axonogenesis and axon extension, regulation and production of bone morphogenetic protein and regulation of cellular growth and development. We gathered a list of significantly associated cardinal maladies for each gene from searchable genomic disease websites, namely MalaCards.org: HGMD, OMIM, ClinVar, GTR, Orphanet, DISEASES, Novoseek, and GeneCards.org. Through tabulations of such disease data, we ascertained the cardinal disease association of each gene, as well as their expanded putative disease associations. This enabled further tabulation of disease data to ascertain the role of each gene in the top ten overlapping significant neurodevelopmental disorders among the disease association data sets: (1) Prader–Willi Syndrome (PWS); (2) Angelman Syndrome (AS); (3) 15q11.2 Deletion Syndrome with Attention Deficit Hyperactive Disorder & Learning Disability; (4) Autism Spectrum Disorder (ASD); (5) Schizophrenia; (6) Epilepsy; (7) Down Syndrome; (8) Microcephaly; (9) Developmental Disorder, and (10) Peripheral Nervous System Disease. The cardinal disease associations for each of the four contiguous 15q11.2 BP1-BP2 genes are NIPA1- Spastic Paraplegia 6; NIPA2—Angelman Syndrome and Prader–Willi Syndrome; CYFIP1—Fragile X Syndrome and Autism; TUBGCP5—Prader–Willi Syndrome. The four genes are individually associated with PWS, ASD, schizophrenia, epilepsy, and Down syndrome. Except for TUBGCP5, the other three genes are associated with AS. Unlike the other genes, TUBGCP5 is also not associated with attention deficit hyperactivity disorder and learning disability, developmental disorder, or peripheral nervous system disease. CYFIP1 was the only gene not associated with microcephaly but was the only gene associated with developmental disorders. Collectively, all four genes were associated with up to three-fourths of the ten overlapping neurodevelopmental disorders and are deleted in this most prevalent known pathogenic copy number variation now recognized among humans with these clinical findings.

A Link between Genetic Disorders and Cellular Impairment, Using Human Induced Pluripotent Stem Cells to Reveal the Functional Consequences of Copy Number Variations in the Central Nervous System-A Close Look at Chromosome 15

Recent cutting-edge human genetics technology has allowed us to identify copy number variations (CNVs) and has provided new insights for understanding causative mechanisms of human diseases. A growing number of studies show that CNVs could be associated with physiological mechanisms linked to evolutionary trigger, as well as to the pathogenesis of various diseases, including cancer, autoimmune disease and mental disorders such as autism spectrum disorders, schizophrenia, intellectual disabilities or attention-deficit/hyperactivity disorder. Their incomplete penetrance and variable expressivity make diagnosis difficult and hinder comprehension of the mechanistic bases of these disorders. Additional elements such as co-presence of other CNVs, genomic background and environmental factors are involved in determining the final phenotype associated with a CNV. Genetically engineered animal models are helpful tools for understanding the behavioral consequences of CNVs. However, the genetic background and the biology of these animal model systems have sometimes led to confusing results. New cellular models obtained through somatic cellular reprogramming technology that produce induced pluripotent stem cells (iPSCs) from human subjects are being used to explore the mechanisms involved in the pathogenic consequences of CNVs. Considering the vast quantity of CNVs found in the human genome, we intend to focus on reviewing the current literature on the use of iPSCs carrying CNVs on chromosome 15, highlighting advantages and limits of this system with respect to mouse model systems.

Treatment-resistant psychotic symptoms and the 15q11.2 BP1-BP2 (Burnside-Butler) deletion syndrome: case report and review of the literature

The 15q11.2 BP1-BP2 (Burnside-Butler) deletion is a rare copy number variant impacting four genes (NIPA1, NIPA2, CYFIP1, and TUBGCP5), and carries increased risks for developmental delay, intellectual disability, and neuropsychiatric disorders (attention-deficit/hyperactivity disorder, autism, and psychosis). In this case report (supported by extensive developmental information and medication history), we present the complex clinical portrait of a 44-year-old woman with 15q11.2 BP1-BP2 deletion syndrome and chronic, treatment-resistant psychotic symptoms who has resided nearly her entire adult life in a long-term state psychiatric institution. Diagnostic and treatment implications are discussed.

From Schizophrenia Genetics to Disease Biology: Harnessing New Concepts and Technologies

Schizophrenia (SZ) is a severe mental disorder afflicting around 1% of the population. It is highly heritable but with complex genetics. Recent research has unraveled a plethora of risk loci for SZ. Accordingly, our conceptual understanding of SZ genetics has been rapidly evolving, from oligogenic models towards polygenic or even omnigenic models. A pressing challenge to the field, however, is the translation of the many genetic findings of SZ into disease biology insights leading to more effective treatments. Bridging this gap requires the integration of genetic findings and functional genomics using appropriate cellular models. Harnessing new technologies, such as the development of human induced pluripotent stem cells (hiPSC) and the CRISPR/Cas-based genome/epigenome editing approach are expected to change our understanding of SZ disease biology to a fundamentally higher level. Here, we discuss some new developments.

Stem cell models of schizophrenia, what have we learned and what is the potential?

Schizophrenia is a complex disorder with clinical manifestations in early adulthood. However, it may start with disruption of brain development caused by genetic or environmental factors, or both. Early deteriorating effects of genetic/environmental factors on neural development might be key to described disease causing mechanisms. Establishing cellular models with cells from affected individual using the induced pluripotent stem cells (iPSC) technology could be used to mimic early neurodevelopment alterations caused by risk genes or environmental stressors. Indeed, cellular models have allowed identification and further study of risk factors and the biological pathways in which they are involved. New advancements in differentiation methods such as defined and robust monolayer protocols and cerebral 3D organoids have made it possible to faithfully mimic neural development and neuronal functionality while CRISPR-editing tools assist to engineer isogenic cell lines to precisely explore genetic variation in polygenic diseases such as schizophrenia. Here we review the current field of iPSC models of schizophrenia and how risk factors can be modelled as well as discussing the common biological pathways involved.

Prenatal diagnosis of a familial 15q11.2 (BP1-BP2) microdeletion encompassing TUBGCP5, CYFIP1, NIPA2 and NIPA1 in a fetus with ventriculomegaly, microcephaly and intrauterine growth restriction on prenatal ultrasound

OBJECTIVE

We present prenatal diagnosis of a 15q11.2 (BP1-BP2) microdeletion encompassing TUBGCP5, CYFIP1, NIPA2 and NIPA1 in a fetus with ventriculomegaly, microcephaly and intrauterine growth restriction (IUGR) on prenatal ultrasound.

CASE REPORT

A 30-year-old, gravida 3, para 2, woman was referred to the hospital for amniocentesis because of fetal ventriculomegaly on prenatal ultrasound. Her husband was 31 years old. The couple had two healthy daughters, and there was no family history of mental disorders and congenital malformations. Amniocentesis revealed a karyotype of 46,XX. Array comparative genomic hybridization (aCGH) analysis on the DNA extracted from uncultured amniocytes revealed a 451.89-kb 15q11.2 microdeletion or arr 15q11.2 (22,765,628-23,217,514) × 1.0 [GRCh37 (hg19)] encompassing TUBGCP5, CYFIP1, NIPA2 and NIPA1. The parental karyotypes were normal. aCGH analysis on the DNAs extracted from parental bloods revealed a 402-kb 15q11.2 microdeletion or arr 15q11.2 (22,815,577-23,217,514) × 1.0 (hg19) encompassing TUBGCP5, CYFIP1, NIPA2 and NIPA1 in the phenotypically normal father. The mother did not have any genomic imbalance. Level II ultrasound at 21 weeks of gestation revealed microcephaly and IUGR. The parents elected to terminate the pregnancy at 22 weeks of gestation, and a female fetus was delivered with a body weight of 448 g (10th centile) and a body length of 26 cm (3rd-10th centile) but no gross abnormalities.

CONCLUSION

Fetuses with a 15q11.2 (BP1-BP2) microdeletion may present ventriculomegaly, microcephaly and IUGR on prenatal ultrasound, and aCGH is helpful for prenatal diagnosis under such a circumstance.

Childhood-Onset Schizophrenia: Insights from Induced Pluripotent Stem Cells

Childhood-onset schizophrenia (COS) is a rare psychiatric disorder characterized by earlier onset, more severe course, and poorer outcome relative to adult-onset schizophrenia (AOS). Even though, clinical, neuroimaging, and genetic studies support that COS is continuous to AOS. Early neurodevelopmental deviations in COS are thought to be significantly mediated through poorly understood genetic risk factors that may also predispose to long-term outcome. In this review, we discuss findings from induced pluripotent stem cells (iPSCs) that allow the generation of disease-relevant cell types from early brain development. Because iPSCs capture each donor's genotype, case/control studies can uncover molecular and cellular underpinnings of COS. Indeed, recent studies identified alterations in neural progenitor and neuronal cell function, comprising dendrites, synapses, electrical activity, glutamate signaling, and miRNA expression. Interestingly, transcriptional signatures of iPSC-derived cells from patients with COS showed concordance with postmortem brain samples from SCZ, indicating that changes in vitro may recapitulate changes from the diseased brain. Considering this progress, we discuss also current caveats from the field of iPSC-based disease modeling and how to proceed from basic studies to improved diagnosis and treatment of COS.

Human iPSC-derived neurons and lymphoblastoid cells for personalized medicine research in neuropsychiatric disorders

The development and clinical implementation of personalized medicine crucially depends on the availability of high-quality human biosamples; animal models, although capable of modeling complex human diseases, cannot reflect the large variation in the human genome, epigenome, transcriptome, proteome, and metabolome. Although the biosamples available from public biobanks that store human tissues and cells may represent the large human diversity for most diseases, these samples are not always sufficient for developing biomarkers for patient-tailored therapies for neuropsychiatric disorders. Postmortem human tissues are available from many biobanks; nevertheless, collections of neuronal human cells from large patient cohorts representing the human diversity remain scarce. Two tools are gaining popularity for personalized medicine research on neuropsychiatric disorders: human induced pluripotent stem cell-derived neurons and human lymphoblastoid cell lines. This review examines and contrasts the advantages and limitations of each tool for personalized medicine research.

Low-Density Neuronal Cultures from Human Induced Pluripotent Stem Cells

Induced pluripotent stem cell (iPSC)-based technologies offer an unprecedented possibility to investigate defects occurring during neuronal differentiation in neuropsychiatric and neurodevelopmental disorders, but the density and intricacy of intercellular connections in neuronal cultures challenge currently available analytic methods. Low-density neuronal cultures facilitate the morphometric and functional analysis of neurons. We describe a differentiation protocol to generate low-density neuronal cultures (∼2,500 neurons/cm²) from human iPSC-derived neural stem cells/early neural progenitor cells. We generated low-density cultures using cells from 3 individuals. We also evaluated the morphometric features of neurons derived from 2 of these individuals, one harboring a microdeletion on chromosome 15q11.2 and the other without the microdeletion. An approximately 7.5-fold increase in the density of dendritic filopodia was observed in the neurons with the microdeletion, consistent with previous reports. Low-density neuronal cultures enable facile and unbiased comparisons of iPSC-derived neurons from different individuals or clones.

Clinical and genetic aspects of the 15q11.2 BP1-BP2 microdeletion disorder

BACKGROUND

The 15q11.2 BP1-BP2 microdeletion (Burnside-Butler susceptibility locus) is an emerging condition with over 200 individuals reported in the literature. TUBGCP5, CFYIP1, NIPA1 and NIPA2 genes are located in this chromosome 15 region and when disturbed individually are known to cause neurological, cognitive or behavioural problems as well as playing a role in both Prader-Willi and Angelman syndromes. These syndromes were the first examples in humans of genomic imprinting and typically caused by a deletion but involving the distal chromosome 15q11-q13 breakpoint BP3 and proximally placed breakpoints BP1 or BP2 of different parental origin. The typical 15q11-q13 deletion involves BP1 and BP3 and the typical type II deletion at BP2 and BP3. Several studies have shown that individuals with the larger type I deletion found in both Prader-Willi and Angelman syndromes are reported with more severe neurodevelopmental symptoms compared to those individuals with the smaller type II deletion.

METHODS

The literature was reviewed and clinical and cytogenetic findings summarised in 200 individuals with this microdeletion along with the role of deleted genes in diagnosis, medical care and counseling of those affected and their family members.

RESULTS

Reported findings in this condition include developmental delays (73% of cases) and language impairment (67%) followed by motor delay (42%), attention deficit disorder/attention deficit hyperactivity disorder (35%) and autism spectrum disorder (27%). The de novo deletion frequency has been estimated at 5 to 22% with low penetrance possibly related to subclinical manifestation or incomplete clinical information on family members. A prevalence of 0.6 to 1.3% has been identified in one study for patients with neurological or behavioural problems presenting for genetic services and chromosomal microarray analysis.

CONCLUSIONS

The summarised results indicate that chromosome 15q11.2 BP1-BP2 microdeletion is emerging as one of the most common cytogenetic abnormalities seen in individuals with intellectual impairment, autism spectrum disorder and other related behavioural or clinical findings, but more research is needed.

Associations between period 3 gene polymorphisms and sleep- /chronotype-related variables in patients with late-life insomnia

A variable number tandem repeat polymorphism (VNTR) in the period 3 (PER3) gene has been associated with heritable sleep and circadian variables, including self-rated chronotypes, polysomnographic (PSG) variables, insomnia and circadian sleep-wake disorders. This report describes novel molecular and clinical analyses of PER3 VNTR polymorphisms to better define their functional consequences. As the PER3 VNTR is located in the exonic (protein coding) region of PER3, we initially investigated whether both alleles (variants) are transcribed into messenger RNA in human fibroblasts. The VNTR showed bi-allelic gene expression. We next investigated genetic associations in relation to clinical variables in 274 older adult Caucasian individuals. Independent variables included genotypes for the PER3 VNTR as well as a representative set of single nucleotide polymorphisms (SNPs) that tag common variants at the PER3 locus (linkage disequilibrium (LD) between genetic variants < 0.5). In order to comprehensively evaluate variables analyzed individually in prior analyses, dependent measures included PSG total sleep time and sleep latency, self-rated chronotype, estimated with the Composite Scale (CS), and lifestyle regularity, estimated using the social rhythm metric (SRM). Initially, genetic polymorphisms were individually analyzed in relation to each outcome variable using analysis of variance (ANOVA). Nominally significant associations were further tested using regression analyses that incorporated individual ANOVA-associated DNA variants as potential predictors and each of the selected sleep/circadian variables as outcomes. The covariates included age, gender, body mass index and an index of medical co-morbidity. Significant genetic associations with the VNTR were not detected with the sleep or circadian variables. Nominally significant associations were detected between SNP rs1012477 and CS scores (p = 0.003) and between rs10462021 and SRM (p = 0.047); rs11579477 and average delta power (p = 0.043) (analyses uncorrected for multiple comparisons). In conclusion, alleles of the VNTR are expressed at the transcript level and may have a functional effect in cells expressing the PER3 gene. PER3 polymorphisms had a modest impact on selected sleep/circadian variables in our sample, suggesting that PER3 is associated with sleep and circadian function beyond VNTR polymorphisms. Further replicate analyses in larger, independent samples are recommended.

Cellular models to study schizophrenia: A systematic review

BACKGROUND

Advancements in cellular reprogramming techniques have made it possible to directly study brain cells from patients with neuropsychiatric disorders. We have systematically reviewed the applications of induced pluripotent stem cells (IPSCs) and their neural derivatives in understanding the biological basis of schizophrenia.

METHOD

We searched the scientific literature published in MEDLINE with the following search strategy: (Pluripotent) AND (Schizophrenia OR Antipsychotic OR Psychosis). Studies written in English that used IPSCs derived from patients with schizophrenia were included.

RESULTS

Out of 23 articles, which had used IPSCs from patients with schizophrenia, neurons or neural stem cells had been derived from them in a majority. Several parameters had been studied; the key cellular phenotypes identified included those of synaptic pathology, neural migration/proliferation deficits, and abnormal oxidative phosphorylation.

CONCLUSION

Cellular modelling using IPSCs could improve the biological understanding of schizophrenia. Emerging findings are consistent with those of other study designs (post-mortem brain expression, animal studies, genome-wide association, brain imaging). Future studies should focus on refined study designs (family-based, pharmacogenomics, gene editing) and a combination of cellular studies with deep clinical phenotyping.

Recurrent 15q11.2 BP1-BP2 microdeletions and microduplications in the etiology of neurodevelopmental disorders

Rare and common CNVs can contribute to the etiology of neurodevelopmental disorders. One of the recurrent genomic aberrations associated with these phenotypes and proposed as a susceptibility locus is the 15q11.2 BP1-BP2 CNV encompassing TUBGCP5, CYFIP1, NIPA2, and NIPA1. Characterizing by array-CGH a cohort of 243 families with various neurodevelopmental disorders, we identified five patients carrying the 15q11.2 duplication and one carrying the deletion. All CNVs were confirmed by qPCR and were inherited, except for one duplication where parents were not available. The phenotypic spectrum of CNV carriers was broad but mainly neurodevelopmental, in line with all four genes being implicated in axonal growth and neural connectivity. Phenotypically normal and mildly affected carriers complicate the interpretation of this aberration. This variability may be due to reduced penetrance or altered gene dosage on a particular genetic background. We evaluated the expression levels of the four genes in peripheral blood RNA and found the expected reduction in the deleted case, while duplicated carriers displayed high interindividual variability. These data suggest that differential expression of these genes could partially account for differences in clinical phenotypes, especially among duplication carriers. Furthermore, urinary Mg²⁺ levels appear negatively correlated with NIPA2 gene copy number, suggesting they could potentially represent a useful biomarker, whose reliability will need replication in larger samples. © 2016 Wiley Periodicals, Inc.

Using Induced Pluripotent Stem Cells to Investigate Complex Genetic Psychiatric Disorders

PURPOSE OF REVIEW

Induced pluripotent stem cells (iPSCs) can be generated from human patient tissue samples, differentiated into any somatic cell type, and studied under controlled culture conditions. We review how iPSCs are used to investigate genetic factors and biological mechanisms underlying psychiatric disorders, and considerations for synthesizing data across studies.

RECENT FINDINGS

Results from patient specific-iPSC studies often reveal cellular phenotypes consistent with postmortem and brain imaging studies. Unpredicted findings illustrate the power of iPSCs as a discovery tool, but may also be attributable to limitations in modeling dynamic neural networks or difficulty in identifying the most affected neural subtype or developmental stage.

SUMMARY

Technological advances in differentiation protocols and organoid generation will enhance our ability to model the salient pathology underlying psychiatric disorders using iPSCs. The field will also benefit from context-driven interpretations of iPSC studies that recognize all potential sources of variability, including differences in patient symptomatology, genetic risk factors and affected cellular subtype.

Reduced CYFIP1 in Human Neural Progenitors Results in Dysregulation of Schizophrenia and Epilepsy Gene Networks

Deletions encompassing the BP1-2 region at 15q11.2 increase schizophrenia and epilepsy risk, but only some carriers have either disorder. To investigate the role of CYFIP1, a gene within the region, we performed knockdown experiments in human neural progenitors derived from donors with 2 copies of each gene at the BP1-2 locus. RNA-seq and cellular assays determined that knockdown of CYFIP1 compromised cytoskeletal remodeling. FMRP targets and postsynaptic density genes, each implicated in schizophrenia, were significantly overrepresented among differentially expressed genes (DEGs). Schizophrenia and/or epilepsy genes, but not those associated with randomly selected disorders, were likewise significantly overrepresented. Mirroring the variable expressivity seen in deletion carriers, marked between-line differences were observed for dysregulation of disease genes. Finally, a subset of DEGs showed a striking similarity to known epilepsy genes and represents novel disease candidates. Results support a role for CYFIP1 in disease and demonstrate that disease-related biological signatures are apparent prior to neuronal differentiation.