Association study and mutation sequencing of genes on chromosome 15q11-q13 identified GABRG3 as a susceptibility gene for autism in Chinese Han population

Emerging Perspectives on Prime Editor Delivery to the Brain

Prime editing shows potential as a precision genome editing technology, as well as the potential to advance the development of next-generation nanomedicine for addressing neurological disorders. However, turning in prime editors (PEs), which are macromolecular complexes composed of CRISPR/Cas9 nickase fused with a reverse transcriptase and a prime editing guide RNA (pegRNA), to the brain remains a considerable challenge due to physiological obstacles, including the blood-brain barrier (BBB). This review article offers an up-to-date overview and perspective on the latest technologies and strategies for the precision delivery of PEs to the brain and passage through blood barriers. Furthermore, it delves into the scientific significance and possible therapeutic applications of prime editing in conditions related to neurological diseases. It is targeted at clinicians and clinical researchers working on advancing precision nanomedicine for neuropathologies.

Genetic Alterations in a Large Population of Italian Patients Affected by Neurodevelopmental Disorders

Neurodevelopmental disorders are a group of complex multifactorial disorders characterized by cognitive impairment, communication deficits, abnormal behaviour, and/or motor skills resulting from abnormal neural development. Copy number variants (CNVs) are genetic alterations often associated with neurodevelopmental disorders. We evaluated the diagnostic efficacy of the array-comparative genomic hybridization (a-CGH) method and its relevance as a routine diagnostic test in patients with neurodevelopmental disorders for the identification of the molecular alterations underlying or contributing to the clinical manifestations. In the present study, we analysed 1800 subjects with neurodevelopmental disorders using a CGH microarray. We identified 208 (7%) pathogenetic CNVs, 2202 (78%) variants of uncertain significance (VOUS), and 504 (18%) benign CNVs in the 1800 patients analysed. Some alterations contain genes potentially related to neurodevelopmental disorders including CHRNA7, ANKS1B, ANKRD11, RBFOX1, ASTN2, GABRG3, SHANK2, KIF1A SETBP1, SNTG2, CTNNA2, TOP3B, CNTN4, CNTN5, and CNTN6. The identification of interesting significant genes related to neurological disorders with a-CGH is therefore an essential step in the diagnostic procedure, allowing a better understanding of both the pathophysiology of these disorders and the mechanisms underlying their clinical manifestations.

Paternal cocaine-seeking motivation defines offspring's vulnerability to addiction by down-regulating GABAergic GABRG3 in the ventral tegmental area

Epidemiological investigations indicate that parental drug abuse experiences significantly influenced the addiction vulnerability of offspring. Studies using animal models have shown that paternal cocaine use and highly motivated drug-seeking behavior are important determinants of offspring addiction susceptibility. However, the key molecules contributing to offspring addiction susceptibility are currently unclear. The motivation for cocaine-seeking behavior in offspring of male rats was compared between those whose fathers self-administered cocaine (SA) and those who were yoked with them and received non-contingent cocaine administrations (Yoke). We found that paternal experience with cocaine-seeking behavior, but not direct cocaine exposure, could lead to increased lever-pressing behavior in male F1 offspring. This effect was observed without significant changes to the dose-response relationship. The transcriptomes of ventral tegmental area (VTA) in offspring were analyzed under both naive state and after self-administration training. Specific transcriptomic changes in response to paternal cocaine-seeking experiences were found, which mainly affected biological processes such as synaptic connections and receptor signaling pathways. Through joint analysis of these candidate genes and parental drug-seeking motivation scores, we found that gamma-aminobutyric acid receptor subunit gamma-3 (Gabrg3) was in the hub position of the drug-seeking motivation-related module network and highly correlated with parental drug-seeking motivation scores. The downregulation of Gabrg3 expression, caused by paternal motivational cocaine-seeking, mainly occurred in GABAergic neurons in the VTA. Furthermore, down-regulating GABAergic Gabrg3 in VTA resulted in an increase in cocaine-seeking behavior in the Yoke F1 group. This down-regulation also reduced transcriptome differences between the Yoke and SA groups, affecting processes related to synaptic formation and neurotransmitter transmission. Taken together, we propose that paternal cocaine-seeking behavior, rather than direct drug exposure, significantly influences offspring addiction susceptibility through the downregulation of Gabrg3 in GABAergic neurons of the VTA, highlighting the importance of understanding specific molecular pathways in the intergenerational inheritance of addiction vulnerability.

Genes positively regulated by Mef2c in cortical neurons are enriched for common genetic variation associated with IQ and educational attainment

The myocyte enhancer factor 2 C (MEF2C) gene encodes a transcription factor important for neurogenesis and synapse development and contains common variants associated with intelligence (IQ) and educational attainment (EA). Here, we took gene expression data from the mouse cortex of a Mef2c mouse model with a heterozygous DNA binding-deficient mutation of Mef2c (Mef2c-het) and combined these data with MEF2C ChIP-seq data from cortical neurons and single-cell data from the mouse brain. This enabled us to create a set of genes that were differentially regulated in Mef2c-het mice, represented direct target genes of MEF2C and had elevated in expression in cortical neurons. We found this gene-set to be enriched for genes containing common genetic variation associated with IQ and EA. Genes within this gene-set that were down-regulated, i.e. have reduced expression in Mef2c-het mice versus controls, were specifically significantly enriched for both EA and IQ associated genes. These down-regulated genes were enriched for functionality in the adenylyl cyclase signalling system, which is known to positively regulate synaptic transmission and has been linked to learning and memory. Within the adenylyl cyclase signalling system, three genes regulated by MEF2C, CRHR1, RGS6, and GABRG3, are associated at genome-wide significant levels with IQ and/or EA. Our results indicate that genetic variation in MEF2C and its direct target genes within cortical neurons contribute to variance in cognition within the general population, and the molecular mechanisms involved include the adenylyl cyclase signalling system's role in synaptic function.

Gamma-Aminobutyric Acid Type A Receptor Variants are Associated with Autism Spectrum Disorders

Despite several efforts to identify the causes of autism spectrum disorders (ASD), its etiology remains still unclear. Among other aspects, genes that encode neurotransmitter receptors are strong candidates for autism. Here, we wanted to study some genetic variants of gamma-aminobutyric acid (GABA) receptor subunit genes GABRB3, GABRG3, and GABRA5, located on chromosome 15q11-q13 that might contribute to the etiology of ASD in the affected children of West Bengal. rs7180158, rs2081648 (GABRB3); rs12910555 (GABRG3); rs35399885, rs35832850 (GABRA5) were analyzed in 316 children with ASD and 227 healthy controls. Phenotypic associations were evaluated by Childhood Autism Rating Scale (CARS). Gene expression levels were measured by quantitative real-time PCR. ASD probands showed a higher frequency of "A" allele for rs7180158, "G" allele for rs12901555, and "T" allele for rs35399885. The GA + AA genotypes (rs7180158) and CT + TT genotypes (rs35399885) were found to confer significant risk towards ASD. rs2081648 was found to have transmission bias in the family. Additionally, these variants were found to be associated with one or more of ASD-associated phenotypic traits. Multifactor dimensionality reduction (MDR) analyses showed mostly independent contributory effects of some of the variants. Again, the gene expression levels of GABRB3, GABRG3, and GABRA5 were downregulated in the cases than the controls. ForGABRA5 rs35399885, the CC genotypes corresponded to higher expression levels compared to the other groups. This study reveals that genetic variants of GABA_A receptor subunit genes are significantly associated with ASD. No data for the mentioned variants are found in the population of West Bengal, India.

Autism Spectrum Disorder: Neurodevelopmental Risk Factors, Biological Mechanism, and Precision Therapy

Autism spectrum disorder (ASD) is a heterogeneous, behaviorally defined neurodevelopmental disorder. Over the past two decades, the prevalence of autism spectrum disorders has progressively increased, however, no clear diagnostic markers and specifically targeted medications for autism have emerged. As a result, neurobehavioral abnormalities, neurobiological alterations in ASD, and the development of novel ASD pharmacological therapy necessitate multidisciplinary collaboration. In this review, we discuss the development of multiple animal models of ASD to contribute to the disease mechanisms of ASD, as well as new studies from multiple disciplines to assess the behavioral pathology of ASD. In addition, we summarize and highlight the mechanistic advances regarding gene transcription, RNA and non-coding RNA translation, abnormal synaptic signaling pathways, epigenetic post-translational modifications, brain-gut axis, immune inflammation and neural loop abnormalities in autism to provide a theoretical basis for the next step of precision therapy. Furthermore, we review existing autism therapy tactics and limits and present challenges and opportunities for translating multidisciplinary knowledge of ASD into clinical practice.

SNP-PCR genotyping links alterations in the GABAA receptor (GABRG3: rs208129) and RELN (rs73670) genes to autism spectrum disorder among peadiatric Iraqi Arabs

INTRODUCTION

Autism spectrum disorder (ASD) is an increasing concern among the Iraqi Arab population. The genetic alterations that cause ASD are likely to converge at the synapse. This study investigated polymorphisms in the GABAA receptor subunit (GABRG3) and the RELN gene as putative biomarkers of ASD in a pediatric population in Iraq.

METHODS

The case control study included 60 patients with a clinical diagnosis of ASD (mild, moderate, or severe) according to DSM-IV criteria and matched healthy controls (n = 60). Blood samples were collected for DNA genotyping of SNPs rs736707 and rs208129 for RELN and GABRG3 using allele specific PCR. Assessment of genotype and allele distributions in patient groups used odd ratios (OR) with 95% confidence intervals and the Chi-square test. All statistical analysis was performed used SPSS software.

RESULT

The patient cohort was highly consanguineous, with increased ratio (p > 0.05) of males to females (3:1) in both ASD (mean age, 6.66 ± 3.05) and controls (mean age, 5.76 ± 2.3). Both GABRG3 rs208129 genotypes TT (OR 4.33, p = 0.0015) and TA (OR 0.259, P = 0.008), and the T and A alleles were significantly associated with ASD. The RELN rs736707 TC genotype (OR 2.626, P = 0.034) was the only significant association with ASD.

CONCLUSION

GABRG3 SNP rs208129 is a leading biomarker to predict genetic vulnerability to ASD in Iraqi Arabs. Expanded SNP panels and increased sample sizes are required for future GABRG3 studies, and to reach a consensus on RELN utility. Future ASD screening programs in Iraq should include genetic metrics in addition to clinical phenotype assessments.

GABA Receptor SNPs and Elevated Plasma GABA Levels Affect the Severity of the Indian ASD Probands

Altered signaling of the chief inhibitory neurotransmitter, gamma-aminobutyric acid (GABA), has been speculated in the etiology of autism spectrum disorder (ASD). We have investigated the association of six GABA_A-receptor genetic variants and plasma GABA levels with ASD. Subjects were recruited based on the DSM, and CARS2-ST and ADI-R assessed disease severity. Peripheral blood was collected from the ASD probands (N = 251), their parents, and ethnically matched controls (N = 347). A positive correlation between the CARS2-ST and ADI-R scores was observed; domain scores of ADI-R were higher in the severe group categorized by the CARS2-ST. GABRB3 rs1432007 "A," GABRG3 rs897173 "A," and GABRA5 rs140682 "T" showed significant association with ASD. Trait scores were influenced by rs1432007 "AA" and rs140682 "TT." GABA level was significantly higher in the probands than the age-matched controls. Our findings indicate an influence of GABA in the etiology of ASD in the Indian probands.

Expanding the clinico-molecular spectrum of Angelman syndrome phenotype with the GABRG3 gene: Evidence from methylation and sequencing studies

Angelman syndrome (AS) (OMIM#105830) is an imprinting disorder caused due to alterations in the maternal chr 15q11-13 region. Majority of cases can be diagnosed by methylation-specific polymerase chain reaction (MS-PCR) of SNRPN gene and by UBE3A sequencing, however, about 10% of cases with AS phenotype remain undiagnosed. Differential diagnoses of AS can be detected by chromosomal microarray (CMA) and clinical exome sequencing (CES). In this study, 30 cases with AS features were evaluated by MS-PCR, CMA, and CES. SNRPN MS-PCR confirmed AS in eight (26%), CMA and CES diagnosed nine (30%) cases. One case was identified with a novel variant c.1125C > T in GABRG3, located at 15q12 region, which is currently not associated with any syndrome. The GABRG3 gene is also speculated to be imprinted, a MS-PCR assay was designed to confirm its differential parental methylation status. This assay identified another case with altered GABRG3 methylation. The two cases with GABRG3 alteration-sequence change and methylation indicate that GABRG3 may be associated with a subtype of AS or a new related syndrome. Performing GABRG3 MS-PCR and sequencing of a larger group of patients with AS phenotype and normal SNPRN and UBE3A status will help in establishing exact genotype-phenotype correlation.

An Association Study of Gamma-Aminobutyric Acid Type A Receptor Variants and Susceptibility to Autism Spectrum Disorders

In this pilot study, we aim to identify the role of few genetic variants of GABA-receptor type A subunits GABRB3 (rs4906902, rs7171660), GABRG3 (rs208129, rs140679), GABRA5 (rs 140681) in the aetiology of autism spectrum disorders in a population of West Bengal. 192 ASD probands, their parents and 184 ethnically-matched healthy controls were recruited for the study. The rs4906902G and the rs140679T conferred significant risk towards ASD. rs7171660 and rs140679 had transmission bias in the family. Neither alleles of rs 208129 and rs 140681 showed significant over-representation in either groups. All these variants were associated with at least one deficit in ASD-associated phenotypes like 'relating to people', 'Imitation', 'emotional response', 'body use', 'taste, smell, touch response' and 'activity levels'.

Combined cellomics and proteomics analysis reveals shared neuronal morphology and molecular pathway phenotypes for multiple schizophrenia risk genes

An enigma in studies of neuropsychiatric disorders is how to translate polygenic risk into disease biology. For schizophrenia, where > 145 significant GWAS loci have been identified and only a few genes directly implicated, addressing this issue is a particular challenge. We used a combined cellomics and proteomics approach to show that polygenic risk can be disentangled by searching for shared neuronal morphology and cellular pathway phenotypes of candidate schizophrenia risk genes. We first performed an automated high-content cellular screen to characterize neuronal morphology phenotypes of 41 candidate schizophrenia risk genes. The transcription factors Tcf4 and Tbr1 and the RNA topoisomerase Top3b shared a neuronal phenotype marked by an early and progressive reduction in synapse numbers upon knockdown in mouse primary neuronal cultures. Proteomics analysis subsequently showed that these three genes converge onto the syntaxin-mediated neurotransmitter release pathway, which was previously implicated in schizophrenia, but for which genetic evidence was weak. We show that dysregulation of multiple proteins in this pathway may be due to the combined effects of schizophrenia risk genes Tcf4, Tbr1, and Top3b. Together, our data provide new biological functions for schizophrenia risk genes and support the idea that polygenic risk is the result of multiple small impacts on common neuronal signaling pathways.

Identification of primary copy number variations reveal enrichment of Calcium, and MAPK pathways sensitizing secondary sites for autism

Background

Autism is a neurodevelopmental condition with genetic heterogeneity. It is characterized by difficulties in reciprocal social interactions with strong repetitive behaviors and stereotyped interests. Copy number variations (CNVs) are genomic structural variations altering the genomic structure either by duplication or deletion. De novo or inherited CNVs are found in 5–10% of autistic subjects with a size range of few kilobases to several megabases. CNVs predispose humans to various diseases by altering gene regulation, generation of chimeric genes, and disruption of the coding region or through position effect. Although, CNVs are not the initiating event in pathogenesis; additional preceding mutations might be essential for disease manifestation. The present study is aimed to identify the primary CNVs responsible for autism susceptibility in healthy cohorts to sensitize secondary-hits. In the current investigation, primary-hit autism gene CNVs are characterized in 1715 healthy cohorts of varying ethnicities across 12 populations using Affymetrix high-resolution array study. Thirty-eight individuals from twelve families residing in Karnataka, India, with the age group of 13–73 years are included for the comparative CNV analysis. The findings are validated against global 179 autism whole-exome sequence datasets derived from Simons Simplex Collection. These datasets are deposited at the Simons Foundation Autism Research Initiative (SFARI) database.

Results

The study revealed that 34.8% of the subjects carried 2% primary-hit CNV burden with 73 singleton-autism genes in different clusters. Of these, three conserved CNV breakpoints were identified with ARHGAP11B, DUSP22, and CHRNA7 as the target genes across 12 populations. Enrichment analysis of the population-specific autism genes revealed two signaling pathways—calcium and mitogen-activated protein kinases (MAPK) in the CNV identified regions. These impaired pathways affected the downstream cascades of neuronal function and physiology, leading to autism behavior. The pathway analysis of enriched genes unravelled complex protein interaction networks, which sensitized secondary sites for autism. Further, the identification of miRNA targets associated with autism gene CNVs added severity to the condition.

Conclusion

These findings contribute to an atlas of primary-hit genes to detect autism susceptibility in healthy cohorts, indicating their impact on secondary sites for manifestation.