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Food addiction is characterized by a loss of behavioral control over food intake and is associated with obesity and other eating disorders. The mechanisms underlying this behavioral disorder are largely unknown. We aimed to investigate the changes in miRNA expression promoted by food addiction in animals and humans and their involvement in the mechanisms underlying the behavioral hallmarks of this disorder. We found sharp similitudes between miRNA signatures in the medial prefrontal cortex (mPFC) of our animal cohort and circulating miRNA levels in our human cohort, which allowed us to identify several miRNAs of potential interest in the development of this disorder. Tough decoy (TuD) inhibition of miRNA-29c-3p in the mouse mPFC promoted persistence of the response and enhanced vulnerability to developing food addiction, whereas miRNA-665-3p inhibition promoted compulsion-like behavior and also enhanced food addiction vulnerability. In contrast, we found that miRNA-137-3p inhibition in the mPFC did not lead to the development of food addiction. Therefore, miRNA-29c3p and miRNA-665-3p could be acting as protective factors with regard to food addiction. We believe the elucidation of these epigenetic mechanisms will lead to advances toward identifying innovative biomarkers and possible future interventions for food addiction and related disorders based on the strategies now available to modify miRNA activity and expression.

Several non-mental diseases seem to be associated with an increased risk of ADHD and ADHD seems to be associated with increased risk for non-mental diseases. The underlying trajectories leading to such brain-body co occurrences are often unclear are there direct causal relationships from one disorder to the other, or does the sharing of genetic and/or environmental risk factors lead to their occurring together more frequently or both? Our goal with this narrative review was to provide a conceptual synthesis of the associations between ADHD and non-mental disease across the lifespan. We discuss potential shared pathologic mechanisms, genetic background and treatments in co-occurring diseases. For those co-occurrences for which published studies with sufficient sample sizes exist, meta-analyses have been published by others and we discuss those in detail. We conclude that non-mental diseases are common in ADHD and vice versa and add to the disease burden of the patient across the lifespan. Insufficient attention to such co-occurring conditions may result in missed diagnoses and suboptimal treatment in the affected individuals.

Psychiatric disorders affect 29% of the global population at least once in the lifespan, and genetic studies have proved a shared genetic basis among them, although the underlying molecular mechanisms remain largely unknown. DNA methylation plays an important role in complex disorders and, remarkably, enrichment of common genetic variants influencing allele-specific methylation (ASM) has been reported among variants associated with specific psychiatric disorders. In the present study we assessed the contribution of ASM to a set of eight psychiatric disorders by combining genetic, epigenetic and expression data. We interrogated a list of 3896 ASM tagSNPs in the brain in the summary statistics of a cross-disorder GWAS meta-analysis of eight psychiatric disorders from the Psychiatric Genomics Consortium, including more than 162,000 cases and 276,000 controls. We identified 80 SNPs with pleiotropic effects on psychiatric disorders that show an opposite directional effect on methylation and gene expression. These SNPs converge on eight candidate genes: ZSCAN29, ZSCAN31, BTN3A2, DDAH2, HAPLN4, ARTN, FAM109B and NAGA. ZSCAN29 shows the broadest pleiotropic effects, showing associations with five out of eight psychiatric disorders considered, followed by ZSCAN31 and BTN3A2, associated with three disorders. All these genes overlap with CNVs related to cognitive phenotypes and psychiatric traits, they are expressed in the brain, and seven of them have previously been associated with specific psychiatric disorders, supporting our results. To sum up, our integrative functional genomics analysis identified eight psychiatric disease risk genes that impact a broad list of disorders and highlight an etiologic role of SNPs that influence DNA methylation and gene expression in the brain.

Genetic variants in YWHAZ contribute to psychiatric disorders such as autism spectrum disorder and schizophrenia, and have been related to an impaired neurodevelopment in humans and mice. Here, we have used zebrafish to investigate the mechanisms by which YWHAZ contributes to neurodevelopmental disorders. We observed that ywhaz expression was pan-neuronal during developmental stages and restricted to Purkinje cells in the adult cerebellum, cells that are described to be reduced in number and size in autistic patients. We then performed whole-brain imaging in wild-type and ywhaz CRISPR/Cas9 knockout (KO) larvae and found altered neuronal activity and connectivity in the hindbrain. Adult ywhaz KO fish display decreased levels of monoamines in the hindbrain and freeze when exposed to novel stimuli, a phenotype that can be reversed with drugs that target monoamine neurotransmission. These findings suggest an important role for ywhaz in establishing neuronal connectivity during development and modulating both neurotransmission and behaviour in adults.

Drug addiction, one of the major health problems worldwide, is characterized by the loss of control in drug intake, craving, and withdrawal. At the individual level, drugs of abuse produce serious consequences on health and have a negative impact on the family environment and on interpersonal and work relationships. At a wider scale, they have significant socio-economic and public health consequences and they cause delinquency and citizen insecurity. Cocaine, a psychostimulant substance, is one of the most used illicit drugs, especially in America, Western Europe, and Australia. Cocaine use disorders (CUD) are complex multifactorial conditions driven by both genetic and environmental influences. Importantly, not all people who use cocaine develop CUD, and this is due, at least in part, to biological factors that are encoded in the genome of individuals. Acute and repeated use of cocaine induces epigenetic and gene expression changes responsible for the neuronal adaptations and the remodeling of brain circuits that lead to the transition from use to abuse or dependence. The purpose of this review is to delineate such factors, which should eventually help to understand the inter-individual variability in the susceptibility to cocaine addiction. Heritability estimates for CUD are high and genetic risk factors for cocaine addiction have been investigated by candidate gene association studies (CGAS) and genome-wide association studies (GWAS), reviewed here. Also, the high comorbidity that exists between CUD and several other psychiatric disorders is well known and includes phenotypes like schizophrenia, aggression, antisocial or risk-taking behaviors. Such comorbidities are associated with a worse lifetime trajectory, and here we report shared genetic factors that may contribute to them. Gene expression changes and epigenetic modifications induced by cocaine use and chronic abuse in humans are addressed by reviewing transcriptomic studies performed on neuronal cells and on postmortem brains. We report some genes which expression is altered by cocaine that also bear genetic risk variants for the disorder. Finally, we have a glance to the pharmacogenetics of CUD treatments, still in early stages. A better understanding of the genetic underpinnings of CUD will foster the search of effective treatments and help to move forward to personalized medicine.

Cocaine addiction is a complex brain disorder involving long-term alterations that lead to loss of control over drug seeking. The transition from recreational use to pathological consumption is different in each individual, depending on the interaction between environmental and genetic factors. Epigenetic mechanisms are ideal candidates to study psychiatric disorders triggered by these interactions, maintaining persistent malfunctions in specific brain regions. Here we aim to study brain-region-specific epigenetic signatures following exposure to cocaine in a mouse model of addiction to this drug. Extreme subpopulations of vulnerable and resilient phenotypes were selected to identify miRNA signatures for differential vulnerability to cocaine addiction. We used an operant model of intravenous cocaine self-administration to evaluate addictive-like behaviour in rodents based on the Diagnostic and Statistical Manual of Mental Disorders Fifth Edition criteria to diagnose substance use disorders. After cocaine self-administration, we performed miRNA profiling to compare two extreme subpopulations of mice classified as resilient and vulnerable to cocaine addiction. We found that mmu-miR-34b-5p was downregulated in the nucleus accumbens of vulnerable mice with high motivation for cocaine. On the other hand, mmu-miR-1249-3p was downregulated on vulnerable mice with high levels of motor disinhibition. The elucidation of the epigenetic profile related to vulnerability to cocaine addiction is expected to help find novel biomarkers that could facilitate the interventions to battle this devastating disorder.

Attention-deficit hyperactivity disorder (ADHD) is a complex neurodevelopmental disorder characterized by hyperactivity, impulsivity, and/or inattention, which are symptoms also observed in many rare genetic disorders. We searched for genes involved in Mendelian disorders presenting with ADHD symptoms in the Online Mendelian Inheritance in Man (OMIM) database, to curate a list of new candidate risk genes for ADHD. We explored the enrichment of functions and pathways in this gene list, and tested whether rare or common variants in these genes are associated with ADHD or with its comorbidities. We identified 139 genes, causal for 137 rare disorders, mainly related to neurodevelopmental and brain function. Most of these Mendelian disorders also present with other psychiatric traits that are often comorbid with ADHD. Using whole exome sequencing (WES) data from 668 ADHD cases, we found rare variants associated with the dimension of the severity of inattention symptoms in three genes: KIF11, WAC, and CRBN. Then, we focused on common variants and identified six genes associated with ADHD (in 19,099 cases and 34,194 controls): MANBA, UQCC2, HIVEP2, FOPX1, KANSL1, and AUH. Furthermore, HIVEP2, FOXP1, and KANSL1 were nominally associated with autism spectrum disorder (ASD) (18,382 cases and 27,969 controls), as well as HIVEP2 with anxiety (7016 cases and 14,475 controls), and FOXP1 with aggression (18,988 individuals), which is in line with the symptomatology of the rare disorders they are responsible for. In conclusion, inspecting Mendelian disorders and the genes responsible for them constitutes a valuable approach for identifying new risk genes and the mechanisms of complex disorders.

Psychiatric disorders are highly prevalent and display considerable clinical and genetic overlap. Dopaminergic and serotonergic neurotransmission have been shown to play an important role in many psychiatric disorders. Here we aim to assess the genetic contribution of these systems to eight psychiatric disorders (attention-deficit hyperactivity disorder (ADHD), anorexia nervosa (ANO), autism spectrum disorder (ASD), bipolar disorder (BIP), major depression (MD), obsessive-compulsive disorder (OCD), schizophrenia (SCZ) and Tourette's syndrome (TS)) using publicly available GWAS analyses performed by the Psychiatric Genomics Consortium that include more than 160,000 cases and 275,000 controls. To do so, we elaborated four different gene sets: two 'wide' selections for dopamine (DA) and for serotonin (SERT) using the Gene Ontology and KEGG pathways tools, and two'core' selections for the same systems, manually curated. At the gene level, we found 67 genes from the DA and/or SERT gene sets significantly associated with one of the studied disorders, and 12 of them were associated with two different disorders. Gene-set analysis revealed significant associations for ADHD and ASD with the wide DA gene set, for BIP with the wide SERT gene set, and for MD with the core SERT set. Interestingly, interrogation of a cross-disorder GWAS meta-analysis of the eight psychiatric conditions displayed association with the wide DA gene set. To our knowledge, this is the first systematic examination of genes encoding proteins essential to the function of these two neurotransmitter systems in these disorders. Our results support a pleiotropic contribution of the dopaminergic and serotonergic systems in several psychiatric conditions.

See Karakaya and Wirth (doi:10.1093/brain/awz273) for a scientific commentary on this article. Neurofascin (NFASC) isoforms are immunoglobulin cell adhesion molecules involved in node of Ranvier assembly. Efthymiou et al. identify biallelic NFASC variants in ten unrelated patients with a neurodevelopmental disorder characterized by variable degrees of central and peripheral involvement. Abnormal expression of Nfasc155 is accompanied by severe loss of myelinated fibres., Axon pathfinding and synapse formation are essential processes for nervous system development and function. The assembly of myelinated fibres and nodes of Ranvier is mediated by a number of cell adhesion molecules of the immunoglobulin superfamily including neurofascin, encoded by the NFASC gene, and its alternative isoforms Nfasc186 and Nfasc140 (located in the axonal membrane at the node of Ranvier) and Nfasc155 (a glial component of the paranodal axoglial junction). We identified 10 individuals from six unrelated families, exhibiting a neurodevelopmental disorder characterized with a spectrum of central (intellectual disability, developmental delay, motor impairment, speech difficulties) and peripheral (early onset demyelinating neuropathy) neurological involvement, who were found by exome or genome sequencing to carry one frameshift and four different homozygous non-synonymous variants in NFASC. Expression studies using immunostaining-based techniques identified absent expression of the Nfasc155 isoform as a consequence of the frameshift variant and a significant reduction of expression was also observed in association with two non-synonymous variants affecting the fibronectin type III domain. Cell aggregation studies revealed a severely impaired Nfasc155-CNTN1/CASPR1 complex interaction as a result of the identified variants. Immunofluorescence staining of myelinated fibres from two affected individuals showed a severe loss of myelinated fibres and abnormalities in the paranodal junction morphology. Our results establish that recessive variants affecting the Nfasc155 isoform can affect the formation of paranodal axoglial junctions at the nodes of Ranvier. The genetic disease caused by biallelic NFASC variants includes neurodevelopmental impairment and a spectrum of central and peripheral demyelination as part of its core clinical phenotype. Our findings support possible overlapping molecular mechanisms of paranodal damage at peripheral nerves in both the immune-mediated and the genetic disease, but the observation of prominent central neurological involvement in NFASC biallelic variant carriers highlights the importance of this gene in human brain development and function.

Drug dependence is a neuropsychiatric condition that involves genetic, epigenetic and environmental factors. Allele-specific methylation (ASM) is a common and stable epigenetic mechanism that involves genetic variants correlating with differential levels of methylation at CpG sites. We selected 182 single-nucleotide polymorphisms (SNPs) described to influence cis ASM in human brain regions to evaluate their possible contribution to drug dependence susceptibility. We performed a case-control association study in a discovery sample of 578 drug-dependent patients (including 428 cocaine-dependent subjects) and 656 controls from Spain, and then, we followed-up the significant associations in an independent sample of 1119 cases (including 589 cocaine-dependent subjects) and 1092 controls. In the discovery sample, we identified five nominal associations, one of them replicated in the follow-up sample (rs6020251). The pooled analysis revealed an association between drug dependence and rs6020251 but also rs11585570, both overcoming the Bonferroni correction for multiple testing. We performed the same analysis considering only cocaine-dependent patients and obtained similar results. The rs6020251 variant correlates with differential methylation levels of cg17974185 and lies in the first intron of the CTNNBL1 gene, in a genomic region with multiple histone marks related to enhancer and promoter regions in brain. Rs11585570 is an eQTL in brain and blood for the SCP2 and ECHDC2 genes and correlates with differential methylation of cg27535305 and cg13461509, located in the promoter regions of both genes. To conclude, using an approach that combines genetic and epigenetic data, we highlighted the CTNNBL1, SCP2 and ECHDC2 genes as potential contributors to drug dependence susceptibility.

Cocaine addiction causes serious health problems, and no effective treatment is available yet. We previously identified a genetic risk variant for cocaine addiction in the PLCB1 gene and found this gene upregulated in postmortem brains of cocaine abusers and in human dopaminergic neuron-like cells after an acute cocaine exposure. Here, we functionally tested the contribution of the PLCB1 gene to cocaine addictive properties using Plcb1+/- mice. First, we performed a general phenotypic characterization and found that Plcb1+/- mice showed normal behavior, although they had increased anxiety and impaired short-term memory. Subsequently, mice were trained for operant conditioning, self-administered cocaine for 10 days, and were tested for cocaine motivation. After extinction, we found a reduction in the cue-induced reinstatement of cocaine-seeking behavior in Plcb1+/- mice. After reinstatement, we identified transcriptomic alterations in the medial prefrontal cortex of Plcb1+/- mice, mostly related to pathways relevant to addiction like the dopaminergic synapse and long-term potentiation. To conclude, we found that heterozygous deletion of the Plcb1 gene decreases cue-induced reinstatement of cocaine-seeking, pointing at PLCB1 as a possible therapeutic target for preventing relapse and treating cocaine addiction.

Genome-wide association studies have discovered hundreds of loci associated with complex brain disorders, but it remains unclear in which cell types these loci are active. Here we integrate genome-wide association study results with single-cell transcriptomic data from the entire mouse nervous system to systematically identify cell types underlying brain complex traits. We show that psychiatric disorders are predominantly associated with projecting excitatory and inhibitory neurons. Neurological diseases were associated with different cell types, which is consistent with other lines of evidence. Notably, Parkinson’s disease was genetically associated not only with cholinergic and monoaminergic neurons (which include dopaminergic neurons) but also with enteric neurons and oligodendrocytes. Using post-mortem brain transcriptomic data, we confirmed alterations in these cells, even at the earliest stages of disease progression. Our study provides an important framework for understanding the cellular basis of complex brain maladies, and reveals an unexpected role of oligodendrocytes in Parkinson’s disease. Eating Disorders Working Group of the Psychiatric Genomics Consortium Roger Adan17,18,19, Lars Alfredsson20, Tetsuya Ando21, Ole Andreassen22, Jessica Baker9, Andrew Bergen23,24, Wade Berrettini25, Andreas Birgegård26,27, Joseph Boden28, Ilka Boehm29, Claudette Boni30, Vesna Boraska Perica31,32, Harry Brandt33, Gerome Breen13,14, Julien Bryois1, Katharina Buehren34, Cynthia Bulik1,9,15, Roland Burghardt35, Matteo Cassina36, Sven Cichon37, Maurizio Clementi36, Jonathan Coleman13,14, Roger Cone38, Philippe Courtet39, Steven Crawford33, Scott Crow40, James Crowley16,26, unna Danner18, Oliver Davis41,42, Martina de Zwaan43, George Dedoussis44, Daniela Degortes45, Janiece DeSocio46, Danielle Dick47, Dimitris Dikeos48, Christian Dina49,50, Monika Dmitrzak-Weglarz51, Elisa Docampo Martinez52,53,54, Laramie Duncan55, Karin Egberts56, Stefan Ehrlich29, Geòrgia Escaramís52,53,54, Tõnu Esko57,58, Xavier Estivill52,53,54,59, Anne Farmer13, Angela Favaro45, Fernando Fernández-Aranda60,61, Manfred Fichter62,63, Krista Fischer57, Manuel Föcker64, Lenka Foretova65, Andreas Forstner37,66,67,68,69, Monica Forzan36, Christopher Franklin31, Steven Gallinger70, Héléna Gaspar13,14, Ina Giegling71, Johanna Giuranna64, Paola Giusti-Rodríquez16, Fragiskos Gonidakis72, Scott Gordon73, Philip Gorwood30,74, Monica Gratacos Mayora52,53,54, Jakob Grove75,76,77,78, Sébastien Guillaume39, Yiran Guo79, Hakon Hakonarson79,80, Katherine Halmi81, Ken Hanscombe82, Konstantinos Hatzikotoulas31, Joanna Hauser83, Johannes Hebebrand64, Sietske Helder13,84, Anjali Henders85, Stefan Herms37,69, Beate Herpertz-Dahlmann34, Wolfgang Herzog86, Anke Hinney64, L. John Horwood28, Christopher Hübel1,13, Laura Huckins31,87, James Hudson88, Hartmut Imgart89, Hidetoshi Inoko90, Vladimir Janout91, Susana Jiménez-Murcia60,61, Craig Johnson92, Jennifer Jordan93,94, Antonio Julià95, Anders Juréus1, Gursharan Kalsi13, Deborah Kaminská96, Allan Kaplan97, Jaakko Kaprio98,99, Leila Karhunen100, Andreas Karwautz101, Martien Kas17,102, Walter Kaye103, James Kennedy97, Martin Kennedy104, Anna Keski-Rahkonen98, Kirsty Kiezebrink105, Youl-Ri Kim106, Katherine Kirk73, Lars Klareskog107, Kelly Klump108, Gun Peggy Knudsen109, Maria La Via9, Mikael Landén1,19, Janne Larsen76,110,111, Stephanie Le Hellard112,113,114, Virpi Leppä1, Robert Levitan115, Dong Li79, Paul Lichtenstein1, Lisa Lilenfeld116, Bochao Danae Lin17, Jolanta Lissowska117, Jurjen Luykx17, Pierre Magistretti118,119, Mario Maj120, Katrin Mannik57,121, Sara Marsal95, Christian Marshall122, Nicholas Martin73, Manuel Mattheisen26,27,75,123, Morten Mattingsdal22, Sara McDevitt124,125, Peter McGuffin13, Sarah Medland73, Andres Metspalu57,126, Ingrid Meulenbelt127, Nadia Micali128,129, James Mitchell130, Karen Mitchell131, Palmiero Monteleone132, Alessio Maria Monteleone120, Grant Montgomery73,85,133, Preben Bo Mortensen76,110,111, Melissa Munn-Chernoff9, Benedetta Nacmias134, Marie Navratilova65, Claes Norring26,27, Ioanna Ntalla44, Catherine Olsen73, Roel Ophoff17,135, Julie O’Toole136, Leonid Padyukov107, Aarno Palotie58,99,137, Jacques Pantel30, Hana Papezova96, Richard Parker73, John Pearson138, Nancy Pedersen1, Liselotte Petersen76,110,111, Dalila Pinto87, Kirstin Purves13, Raquel Rabionet139,140,141, Anu Raevuori98, Nicolas Ramoz30, Ted Reichborn-Kjennerud109,142, Valdo Ricca134,143, Samuli Ripatti144, Stephan Ripke145,146,147, Franziska Ritschel29,148, Marion Roberts13, Alessandro Rotondo149, Dan Rujescu62,71, Filip Rybakowski150, Paolo Santonastaso151, André Scherag152, Stephen Scherer153, ulrike Schmidt13, Nicholas Schork154, Alexandra Schosser155, Jochen Seitz34, Lenka Slachtova156, P. Eline Slagboom127, Margarita Slof-Op ‘t Landt157,158, Agnieszka Slopien159, Sandro Sorbi134,160, Michael Strober161,162, Garret Stuber9,163, Patrick Sullivan1,16, Beata Świątkowska164, Jin Szatkiewicz16, Ioanna Tachmazidou31, Elena Tenconi45, Laura Thornton9, Alfonso Tortorella165,166, Federica Tozzi167, Janet Treasure13, Artemis Tsitsika168, Marta Tyszkiewicz-Nwafor150, Konstantinos Tziouvas169, Annemarie van Elburg18,170, Eric van Furth157,158, Tracey Wade171, Gudrun Wagner101, Esther Walton29, Hunna Watson9,10,11, Thomas Werge172, David Whiteman73, Elisabeth Widen99, D. Blake Woodside173,174, Shuyang Yao1, Zeynep Yilmaz9,16, Eleftheria Zeggini31,175, Stephanie Zerwas9 and Stephan Zipfel176 17Brain Center Rudolf Magnus, Department of Translational Neuroscience, University Medical Center Utrecht, Utrecht, the Netherlands. 18Center for Eating Disorders Rintveld, Altrecht Mental Health Institute, Zeist, the Netherlands. 19Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden. 20Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden. 21Department of Behavioral Medicine, National Institute of Mental Health, National Center of Neurology and Psychiatry, Tokyo, Japan. 22NORMENT KG Jebsen Centre, Division of Mental Health and Addiction, University of Oslo, Oslo University Hospital, Oslo, Norway. 23BioRealm, LLC, Walnut, CA, USA. 24Oregon Research Institute, Eugene, OR, USA. 25Department of Psychiatry, Center for Neurobiology and Behavior, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA. 26Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden. 27Center for Psychiatry Research, Stockholm Health Care Services, Stockholm City Council, Stockholm, Sweden. 28Christchurch Health and Development Study, University of Otago, Christchurch, New Zealand. 29Division of Psychological and Social Medicine and Developmental Neurosciences, Faculty of Medicine, Technische Universität Dresden, Dresden, Germany. 30INSERM U894, Centre of Psychiatry and Neuroscience, Paris, France. 31Wellcome Sanger Institute, Hinxton, Cambridge, UK. 32Department of Medical Biology, School of Medicine, University of Split, Split, Croatia. 33The Center for Eating Disorders at Sheppard Pratt, Baltimore, MD, USA. 34Department of Child and Adolescent Psychiatry, Psychosomatics and Psychotherapy, RWTH Aachen University, Aachen, Germany. 35Klinikum Frankfurt/Oder, Frankfurt, Germany. 36Clinical Genetics Unit, Department of Woman and Child Health, University of Padova, Padua, Italy. 37Institute of Medical Genetics and Pathology, University Hospital Basel, Basel, Switzerland. 38Life Sciences Institute and Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI, USA. 39Department of Emergency Psychiatry and Post-Acute Care, CHRU Montpellier, University of Montpellier, Montpellier, France. 40Department of Psychiatry, University of Minnesota, Minneapolis, MN, USA. 41MRC Integrative Epidemiology Unit, University of Bristol, Bristol, UK. 42School of Social and Community Medicine, University of Bristol, Bristol, UK. 43Department of Psychosomatic Medicine and Psychotherapy, Hannover Medical School, Hannover, Germany. 44Department of Nutrition and Dietetics, Harokopio University, Athens, Greece. 45Department of Neurosciences, University of Padova, Padua, Italy. 46College of Nursing, Seattle University, Seattle, WA, USA. 47Department of Psychology, Virginia Commonwealth University, Richmond, VA, USA. 48Department of Psychiatry, Athens University Medical School, Athens University, Athens, Greece. 49L’institut du thorax, INSERM, CNRS, UNIV Nantes, Nantes, France. 50L’institut du thorax, CHU Nantes, Nantes, France. 51Department of Psychiatric Genetics, Poznań University of Medical Sciences, Poznań, Poland. 52Barcelona Institute of Science and Technology, Barcelona, Spain. 53Universitat Pompeu Fabra, Barcelona, Spain. 54Centro de Investigación Biomédica en Red en Epidemiología y Salud Pública (CIBERESP), Barcelona, Spain. 55Department of Psychiatry and Behavioral Sciences, Stanford University Stanford, CA, USA. 56Department of Child and Adolescent Psychiatry, Psychosomatics and Psychotherapy, University Hospital of Würzburg, Centre for Mental Health, Würzburg, Germany. 57Estonian Genome Center, University of Tartu, Tartu, Estonia. 58Program in Medical and Population Genetics, Broad Institute of the Massachusetts Institute of Technology and Harvard University, Cambridge, MA, USA. 59Genomics and Disease, Bioinformatics and Genomics Programme, Centre for Genomic Regulation, Barcelona, Spain. 60Department of Psychiatry, University Hospital of Bellvitge –IDIBELL and CIBERobn, Barcelona, Spain. 61Department of Clinical Sciences, School of Medicine, University of Barcelona, Barcelona, Spain. 62Department of Psychiatry and Psychotherapy, Ludwig-Maximilians-University (LMU), Munich, Germany. 63Schön Klinik Roseneck affiliated with the Medical Faculty of the University of Munich (LMU), Munich, Germany. 64Department of Child and Adolescent Psychiatry, University Hospital Essen, University of Duisburg-Essen, Essen, Germany. 65Department of Cancer, Epidemiology and Genetics, Masaryk Memorial Cancer Institute, Brno, Czech Republic. 66Institute of Human Genetics, University of Bonn School of Medicine & University Hospital Bonn, Bonn, Germany. 67Department of Genomics, Life and Brain Center, University of Bonn, Bonn, Germany. 68Department of Psychiatry (UPK), University of Basel, Basel, Switzerland. 69Department of Biomedicine, University of Basel, Basel, Switzerland. 70Department of Surgery, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada. 71Department of Psychiatry, Psychotherapy and Psychosomatics, Martin Luther University of Halle-Wittenberg, Halle, Germany. 721st Psychiatric Department, National and Kapodistrian University of Athens, Medical School, Eginition Hospital, Athens, Greece. 73QIMR Berghofer Medical Research Institute, Brisbane, Queensland, Australia. 74CMME (Groupe Hospitalier Sainte-Anne), Paris Descartes University, Paris, France. 75Department of Biomedicine, Aarhus University, Aarhus, Denmark. 76The Lundbeck Foundation Initiative for Integrative Psychiatric Research (iPSyCH), Aarhus, Denmark. 77Centre for Integrative Sequencing, iSEQ, Aarhus University, Aarhus, Denmark. 78Bioinformatics Research Centre, Aarhus University, Aarhus, Denmark. 79Center for Applied Genomics, Children’s Hospital of Philadelphia, Philadelphia, PA, USA. 80Department of Pediatrics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA. 81Department of Psychiatry, Weill Cornell Medical College, New york, Ny, USA. 82Department of Medical and Molecular Genetics, King’s College London, Guy’s Hospital, London, UK. 83Department of Adult Psychiatry, Poznań University of Medical Sciences, Poznań, Poland. 84Zorg op Orde, Leidschendam, the Netherlands. 85Institute for Molecular Bioscience, University of Queensland, Brisbane, Queensland, Australia. 86Department of General Internal Medicine and Psychosomatics, Heidelberg University Hospital, Heidelberg University, Heidelberg, Germany. 87Department of Psychiatry, and Genetics and Genomics Sciences, Division of Psychiatric Genomics, Icahn School of Medicine at Mount Sinai, New york, Ny, USA. 88Biological Psychiatry Laboratory, McLean Hospital/Harvard Medical School, Boston, MA, USA. 89Eating Disorders Unit, Parklandklinik, Bad Wildungen, Germany. 90Department of Molecular Life Science, Division of Basic Medical Science and Molecular Medicine, School of Medicine, Tokai University, Isehara, Japan. 91Faculty of Health Sciences, Palacky University, Olomouc, Czech Republic. 92Eating Recovery Center, Denver, CO, USA. 93Department of Psychological Medicine, University of Otago, Christchurch, New Zealand. 94Canterbury District Health Board, Christchurch, New Zealand. 95Rheumatology Research Group, Vall d’Hebron Research Institute, Barcelona, Spain. 96Department of Psychiatry, First Faculty of Medicine, Charles University, Prague, Czech Republic. 97Center for Addiction and Mental Health, Department of Psychiatry, Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada. 98Department of Public Health, University of Helsinki, Helsinki, Finland. 99Institute for Molecular Medicine Finland, Helsinki Institute of Life Science, University of Helsinki, Helsinki, Finland. 100Institute of Public Health and Clinical Nutrition, Department of Clinical Nutrition, University of Eastern Finland, Kuopio, Finland. 101Eating Disorders Unit, Department of Child and Adolescent Psychiatry, Medical University of Vienna, Vienna, Austria. 102Groningen Institute for Evolutionary Life Sciences, University of Groningen, Groningen, the Netherlands. 103Department of Psychiatry, University of California San Diego, San Diego, CA, USA. 104Department of Pathology and Biomedical Science, University of Otago, Christchurch, New Zealand. 105Health Services Research Unit, University of Aberdeen, Aberdeen, UK. 106Department of Psychiatry, Seoul Paik Hospital, Inje University, Seoul, Korea. 107Rheumatology Unit, Department of Medicine, Center for Molecular Medicine, Karolinska Institutet and Karolinska University Hospital, Stockholm, Sweden. 108Department of Psychology, Michigan State University, East Lansing, MI, USA. 109Department of Mental Disorders, Norwegian Institute of Public Health, Oslo, Norway. 110National Centre for Register-Based Research, Aarhus BSS, Aarhus University, Aarhus, Denmark. 111Centre for Integrated Register-based Research (CIRRAU), Aarhus University, Aarhus, Denmark. 112Department of Clinical Science, K.G. Jebsen Centre for Psychosis Research, Norwegian Centre for Mental Disorders Research (NORMENT), University of Bergen, Bergen, Norway. 113Dr. Einar Martens Research Group for Biological Psychiatry, Center for Medical Genetics and Molecular Medicine, Haukeland University Hospital, Bergen, Norway. 114Department of Clinical Medicine, Laboratory Building, Haukeland University Hospital, Bergen, Norway. 115Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada. 116American School of Professional Psychology, Argosy University, Northern Virginia, Arlington, VA, USA. 117Department of Cancer Epidemiology and Prevention, M Skłodowska-Curie Cancer Center - Oncology Center, Warsaw, Poland. 118BESE Division, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia. 119Department of Psychiatry, University of Lausanne-University Hospital of Lausanne (UNIL-CHUV), Lausanne, Switzerland. 120Department of Psychiatry, University of Campania ‘Luigi Vanvitelli’, Naples, Italy. 121Center for Integrative Genomics, University of Lausanne, Lausanne, Switzerland. 122Department of Paediatric Laboratory Medicine, The Hospital for Sick Children, Toronto, Ontario, Canada. 123Department of Psychiatry, Psychosomatics and Psychotherapy, University of Würzburg, Würzburg, Germany. 124Department of Psychiatry, University College Cork, Cork, Ireland. 125Eist Linn Adolescent Unit, Bessborough, Health Service Executive South, Cork, Ireland. 126Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia. 127Molecular Epidemiology Section (Department of Medical Statistics), Leiden University Medical Centre, Leiden, the Netherlands. 128Department of Psychiatry, Faculty of Medicine, University of Geneva, Geneva, Switzerland. 129Division of Child and Adolescent Psychiatry, Geneva University Hospital, Geneva, Switzerland. 130Department of Psychiatry and Behavioral Science, University of North Dakota School of Medicine and Health Sciences, Fargo, ND, USA. 131National Center for PTSD, VA Boston Healthcare System, Department of Psychiatry, Boston University School of Medicine, Boston, MA, USA. 132Department of Medicine, Surgery and Dentistry ‘Scuola Medica Salernitana’, University of Salerno, Salerno, Italy. 133Queensland Brain Institute, University of Queensland, Brisbane, Queensland, Australia. 134Department of Neuroscience, Psychology, Drug Research and Child Health (NEUROFARBA), University of Florence, Florence, Italy. 135Center for Neurobehavioral Genetics, Semel Institute for Neuroscience and Human Behavior, University of California Los Angeles, Los Angeles, CA, USA. 136Kartini Clinic, Portland, OR, USA. 137Center for Human Genome Research at the Massachusetts General Hospital, Boston, MA, USA. 138Biostatistics and Computational Biology Unit, University of Otago, Christchurch, New Zealand. 139Saint Joan de Déu Research Institute, Saint Joan de Déu Barcelona Children’s Hospital, Barcelona, Spain. 140Institute of Biomedicine (IBUB), University of Barcelona, Barcelona, Spain. 141Department of Genetics, Microbiology and Statistics, University of Barcelona, Barcelona, Spain. 142Institute of Clinical Medicine, University of Oslo, Oslo, Norway. 143Department of Health Science, University of Florence, Florence, Italy. 144Department of Biometry, University of Helsinki, Helsinki, Finland. 145Analytic and Translational Genetics Unit, Massachusetts General Hospital, Boston, MA, USA. 146Stanley Center for Psychiatric Research, Broad Institute of the Massachusetts Institute of Technology and Harvard University, Cambridge, MA, USA. 147Department of Psychiatry and Psychotherapy, Charité - Universitätsmedizin, Berlin, Germany. 148Eating Disorders Research and Treatment Center, Department of Child and Adolescent Psychiatry, Faculty of Medicine, Technische Universität Dresden, Dresden, Germany. 149Department of Psychiatry, Neurobiology, Pharmacology, and Biotechnologies, University of Pisa, Pisa, Italy. 150Department of Psychiatry, Poznań University of Medical Sciences, Poznań, Poland. 151Department of Neurosciences, Padua Neuroscience Center, University of Padova, Padua, Italy. 152Institute of Medical Statistics, Computer and Data Sciences, Jena University Hospital, Jena, Germany. 153Department of Genetics and Genomic Biology, The Hospital for Sick Children, Toronto, Ontario, Canada. 154J. Craig Venter Institute (JCVI), La Jolla, CA, USA. 155Department of Psychiatry and Psychotherapy, Medical University of Vienna, Vienna, Austria. 156Department of Pediatrics and Center of Applied Genomics, First Faculty of Medicine, Charles University, Prague, Czech Republic. 157Center for Eating Disorders Ursula, Rivierduinen, Leiden, the Netherlands. 158Department of Psychiatry, Leiden University Medical Centre, Leiden, the Netherlands. 159Department of Child and Adolescent Psychiatry, Poznań University of Medical Sciences, Poznań, Poland. 160IRCCS Fondazione Don Carlo Gnocchi, Florence, Italy. 161Department of Psychiatry and Biobehavioral Science, Semel Institute for Neuroscience and Human Behavior, University of California Los Angeles, Los Angeles, CA, USA. 162David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA, USA. 163Department of Cell Biology and Physiology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA. 164Department of Environmental Epidemiology, Nofer Institute of Occupational Medicine, Lodz, Poland. 165Department of Psychiatry, University of Naples SUN, Naples, Italy. 166Department of Psychiatry, University of Perugia, Perugia, Italy. 167Brain Sciences Department, Stremble Ventures, Limassol, Cyprus. 168Adolescent Health Unit, Second Department of Pediatrics, ‘P. & A. Kyriakou’ Children’s Hospital, University of Athens, Athens, Greece. 169Pediatric Intensive Care Unit, ‘P. & A. Kyriakou’ Children’s Hospital, University of Athens, Athens, Greece. 170Faculty of Social and Behavioral Sciences, Utrecht University, Utrecht, the Netherlands. 171School of Psychology, Flinders University, Adelaide, South Australia, Australia. 172Department of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark. 173Department of Psychiatry, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada. 174Toronto General Hospital, Toronto, Ontario, Canada. 175Institute of Translational Genomics, Helmholtz Zentrum München, Neuherberg, Germany. 176Department of Internal Medicine VI, Psychosomatic Medicine and Psychotherapy, University Medical Hospital Tübingen, Tübingen, Germany International Headache Genetics Consortium Verneri Anttila177, Ville Artto178, Andrea Carmine Belin179, Irene de Boer180, Dorret I. Boomsma181, Sigrid Børte182, Daniel I. Chasman183, Lynn Cherkas184, Anne Francke Christensen185, Bru Cormand186, Ester Cuenca-Leon177, George Davey-Smith187, Martin Dichgans188, Cornelia van Duijn189, Tonu Esko57, Ann Louise Esserlind190, Michel Ferrari180, Rune R. Frants180, Tobias Freilinger191, Nick Furlotte192, Padhraig Gormley177, Lyn Griffiths193, Eija Hamalainen194, Thomas Folkmann Hansen6, Marjo Hiekkala195, M. Arfan Ikram189, Andres Ingason196, Marjo-Riitta Järvelin197, Risto Kajanne194, Mikko Kallela178, Jaakko Kaprio98,99, Mari Kaunisto195, Lisette J. A. Kogelman6, Christian Kubisch198, Mitja Kurki177, Tobias Kurth199, Lenore Launer200, Terho Lehtimaki201, Davor Lessel198, Lannie Ligthart181, Nadia Litterman192, Arn van den Maagdenberg180, Alfons Macaya202, Rainer Malik188, Massimo Mangino184, George McMahon187, Bertram Muller-Myhsok203, Benjamin M. Neale177, Carrie Northover192, Dale R. Nyholt193, Jes Olesen190, Aarno Palotie58,99,137, Priit Palta194, Linda Pedersen182, Nancy Pedersen1, Danielle Posthuma181, Patricia Pozo-Rosich204, Alice Pressman205, Olli Raitakari206, Markus Schürks199, Celia Sintas186, Kari Stefansson196, Hreinn Stefansson196, Stacy Steinberg196, David Strachan207, Gisela Terwindt180, Marta Vila-Pueyo202, Maija Wessman195, Bendik S. Winsvold182, Huiying Zhao193 and John Anker Zwart182 177Broad Institute of MIT and Harvard, Cambridge, MA, USA. 178Department of Neurology, Helsinki University Central Hospital, Helsinki, Finland. 179Karolinska Institutet, Stockholm, Sweden. 180Leiden University Medical Centre, Leiden, the Netherlands. 181VU University, Amsterdam, the Netherlands. 182Oslo University Hospital and University of Oslo, Oslo, Norway. 183Harvard Medical School, Cambridge, MA, USA. 184Department of Twin Research and Genetic Epidemiology, King’s College London, London, UK. 185Danish Headache Center, Copenhagen University Hospital, Copenhagen, Denmark. 186University of Barcelona, Barcelona, Spain. 187Medical Research Council (MRC) Integrative Epidemiology Unit, University of Bristol, Bristol, UK. 188Institute for Stroke and Dementia Research, Munich, Germany. 189Erasmus University Medical Centre, Rotterdam, the Netherlands. 190Danish Headache Center, Department of Neurology, Rigshospitalet, Glostrup, Denmark. 191University of Tübingen, Tübingen, Germany. 19223&Me Inc., Mountain View, CA, USA. 193Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Queensland, Australia. 194Institute for Molecular Medicine Finland (FIMM), University of Helsinki, Helsinki, Finland. 195Folkhälsan Institute of Genetics, Helsinki, Finland. 196Decode genetics Inc., Reykjavik, Iceland. 197University of Oulu, Biocenter Oulu, Finland. 198University Medical Center Hamburg-Eppendorf, Hamburg, Germany. 199Harvard Medical School, Boston, MA, USA. 200National Institute on Aging, Bethesda, MD, USA. 201School of Medicine, University of Tampere, Tampere, Finland. 202Vall d’Hebron Research Institute, Barcelona, Spain. 203Max Planck Institute of Psychiatry, Munich, Germany. 204Headache Research Group, Universitat Autònoma de Barcelona, Barcelona, Spain. 205Sutter Health, Sacramento, CA, USA. 206Department of Medicine, University of Turku, Turku, Finland. 207Population Health Research Institute, St George’s University of London, London, UK. 23andMe Research Team Michelle Agee208, Babak Alipanahi208, Adam Auton208, Robert Bell208, Katarzyna Bryc208, Sarah Elson208, Pierre Fontanillas208, Nicholas Furlotte208, Karl Heilbron208, David Hinds208, Karen Huber208, Aaron Kleinman208, Nadia Litterman208, Jennifer McCreight208, Matthew McIntyre208, Joanna Mountain208, Elizabeth Noblin208, Carrie Northover208, Steven Pitts208, J. Sathirapongsasuti208, Olga Sazonova208, Janie Shelton208, Suyash Shringarpure208, Chao Tian208, Joyce Tung208, Vladimir Vacic208 and Catherine Wilson208 20823andMe, Inc., Mountain View, CA, US

Genome-wide association studies have discovered hundreds of loci associated with complex brain disorders, but it remains unclear in which cell types these loci are active. Here we integrate genome-wide association study results with single-cell transcriptomic data from the entire mouse nervous system to systematically identify cell types underlying brain complex traits. We show that psychiatric disorders are predominantly associated with projecting excitatory and inhibitory neurons. Neurological diseases were associated with different cell types, which is consistent with other lines of evidence. Notably, Parkinson’s disease was genetically associated not only with cholinergic and monoaminergic neurons (which include dopaminergic neurons) but also with enteric neurons and oligodendrocytes. Using post-mortem brain transcriptomic data, we confirmed alterations in these cells, even at the earliest stages of disease progression. Our study provides an important framework for understanding the cellular basis of complex brain maladies, and reveals an unexpected role of oligodendrocytes in Parkinson’s disease. © 2020, The Author(s), under exclusive licence to Springer Nature America, Inc.

Background: Recently, RBFOX1, a gene encoding an RNA binding protein, has consistently been associated with aggressive and antisocial behavior. Several loci in the gene have been nominally associated with aggression in genome-wide association studies, the risk alleles being more frequent in the general population. We have hence examined the association of four RBFOX1 single nucleotide polymorphisms, previously found related to aggressive traits, with aggressiveness, personality, and alcohol use disorder in birth cohort representative samples. Methods: We used both birth cohorts of the Estonian Children Personality Behavior and Health Study (ECPBHS; original n = 1,238). Aggressiveness was assessed using the Buss-Perry Aggression Questionnaire and the Lifetime History of Aggressiveness structured interview at age 25 (younger cohort) or 33 (older cohort). Big Five personality at age 25 was measured with self-reports and the lifetime occurrence of alcohol use disorder assessed with the MINI interview. RBFOX1 polymorphisms rs809682, rs8062784, rs12921846, and rs6500744 were genotyped in all participants. Given the restricted size of the sample, correction for multiple comparisons was not applied. Results: Aggressiveness was not significantly associated with the RBFOX1 genotype. RBFOX1 rs8062784 was associated with neuroticism and rs809682 with extraversion. Two out of four analyzed RBFOX1 variants, rs8062784 and rs12921846, were associated with the occurrence of alcohol use disorder. Conclusions: In the birth cohort representative sample of the ECPBHS, no association of RBFOX1 with aggressiveness was found, but RBFOX1 variants affected basic personality traits and the prevalence of alcohol use disorder. Future studies on RBFOX1 should consider the moderating role of personality and alcohol use patterns in aggressiveness.

Attention deficit/hyperactivity disorder (ADHD) is a common neurodevelopmental disorder characterized by age-inappropriate symptoms of inattention, impulsivity, and hyperactivity that persist into adulthood in the majority of the diagnosed children. Despite several risk factors during childhood predicting the persistence of ADHD symptoms into adulthood, the genetic architecture underlying the trajectory of ADHD over time is still unclear. We set out to study the contribution of common genetic variants to the risk for ADHD across the lifespan by conducting meta-analyses of genome-wide association studies on persistent ADHD in adults and ADHD in childhood separately and jointly, and by comparing the genetic background between them in a total sample of 17,149 cases and 32,411 controls. Our results show nine new independent loci and support a shared contribution of common genetic variants to ADHD in children and adults. No subgroup heterogeneity was observed among children, while this group consists of future remitting and persistent individuals. We report similar patterns of genetic correlation of ADHD with other ADHD-related datasets and different traits and disorders among adults, children, and when combining both groups. These findings confirm that persistent ADHD in adults is a neurodevelopmental disorder and extend the existing hypothesis of a shared genetic architecture underlying ADHD and different traits to a lifespan perspective.

The RBFOX1 gene (or A2BP1) encodes a splicing factor important for neuronal development that has been related to autism spectrum disorder and other neurodevelopmental phenotypes. Evidence from complementary sources suggests that this gene contributes to aggressive behavior. Suggestive associations with RBFOX1 have been identified in genome-wide association studies (GWAS) of anger, conduct disorder, and aggressive behavior. Nominal association signals in RBFOX1 were also found in an epigenome-wide association study (EWAS) of aggressive behavior. Also, variants in this gene affect temporal lobe volume, a brain area that is altered in several aggression-related phenotypes. In animals, this gene has been shown to modulate aggressive behavior in Drosophila. RBFOX1 has also been associated with canine aggression and is upregulated in mice that show increased aggression after frustration of an expected reward. Associated common genetic variants as well as rare duplications and deletions affecting RBFOX1 have been identified in several psychiatric and neurodevelopmental disorders that are often comorbid with aggressive behaviors. In this paper, we comprehensively review the cumulative evidence linking RBFOX1 to aggression behavior and provide new results implicating RBFOX1 in this phenotype. Most of these studies (genetic and epigenetic analyses in humans, neuroimaging genetics, gene expression and animal models) are hypothesis-free, which strengthens the validity of the findings, although all the evidence is nominal and should therefore be taken with caution. Further studies are required to clarify in detail the role of this gene in this complex phenotype.

The nuclear factor of activated T-cells 5 (NFAT5), also known as tonicity-responsive enhancer-binding protein (TonEBP), is a transcription factor that regulates osmoadaptive response in multiple tissues and is highly expressed in the developing central nervous system. A former study reported that NFAT5 activation through hypertonic stress increases the expression of the dopa decarboxylase enzyme (DDC), also known as aromatic-l-amino-acid decarboxylase (AADC), in human renal proximal tubule cells, leading to an increase of dopamine synthesis. In a previous study, we identified NFAT5 as a candidate gene for cocaine dependence, a complex psychiatric disorder in which dopaminergic neurotransmission plays an important role. Therefore, to test the hypothesis that NFAT5 may also affect dopamine levels in the nervous system through the regulation of DDC expression, we examined this regulation using two neural dopaminergic cell lines, SH-SY5Y and PC12. The effect of NFAT5 on the expression of the neuronal isoform of DDC was evaluated by qRT-PCR. Upon hypertonic stress, NFAT5 was activated and accumulated into the nuclei and, subsequently, the expression of NFAT5 and its known targets sodium/myo-inositol cotransporter 1 (SMIT) and sodium chloride/taurine cotransporter (TAUT) increased, as expected. However, the expression of DDC decreased. When silencing the expression of NFAT5 with a specific shRNA we observed that the downregulation of DDC is independent from NFAT5 in both cell lines and is due to hypertonic stress. In conclusion, NFAT5 does not regulate the expression of the neuronal isoform of DDC in neural dopaminergic cell lines and, consequently, it does not modulate dopamine synthesis through DDC.

Mice lacking GAD1 show neonatal mortality, but the human phenotype associated with GAD1 disruption is poorly characterized. Neuray et al. describe six patients with biallelic GAD1 mutations, presenting with early-infantile onset epilepsy, neurodevelopmental delay, muscle weakness and non-CNS manifestations., Gamma-aminobutyric acid (GABA) and glutamate are the most abundant amino acid neurotransmitters in the brain. GABA, an inhibitory neurotransmitter, is synthesized by glutamic acid decarboxylase (GAD). Its predominant isoform GAD67, contributes up to ∼90% of base-level GABA in the CNS, and is encoded by the GAD1 gene. Disruption of GAD1 results in an imbalance of inhibitory and excitatory neurotransmitters, and as Gad1−/− mice die neonatally of severe cleft palate, it has not been possible to determine any potential neurological dysfunction. Furthermore, little is known about the consequence of GAD1 disruption in humans. Here we present six affected individuals from six unrelated families, carrying bi-allelic GAD1 variants, presenting with developmental and epileptic encephalopathy, characterized by early-infantile onset epilepsy and hypotonia with additional variable non-CNS manifestations such as skeletal abnormalities, dysmorphic features and cleft palate. Our findings highlight an important role for GAD1 in seizure induction, neuronal and extraneuronal development, and introduce GAD1 as a new gene associated with developmental and epileptic encephalopathy.