Mutations in ASH1L confer susceptibility to Tourette syndrome

The genetics of trichotillomania and excoriation disorder: A systematic review

BACKGROUND

Trichotillomania (TTM) and excoriation disorder (ED) are impairing obsessive-compulsive related disorders that are common in the general population and for which there are no clear first-line medications, highlighting the need to better understand the underlying biology of these disorders to inform treatments. Given the importance of genetics in obsessive-compulsive disorder (OCD), evaluating genetic factors underlying TTM and ED may advance knowledge about the pathophysiology of these body-focused repetitive behaviors.

AIM

In this systematic review, we summarize the available evidence on the genetics of TTM and ED and highlight gaps in the field warranting further research.

METHOD

We systematically searched Embase, PsycInfo, PubMed, Medline, Scopus, and Web of Science for original studies in genetic epidemiology (family or twin studies) and molecular genetics (candidate gene and genome-wide) published up to June 2023.

RESULTS

Of the 3536 records identified, 109 studies were included in this review. These studies indicated that genetic factors play an important role in the development of TTM and ED, some of which may be shared across the OCD spectrum, but there are no known high-confidence specific genetic risk factors for either TTM or ED.

CONCLUSIONS

Our review underscores the need for additional genome-wide research conducted on the genetics of TTM and ED, for instance, genome-wide association and whole-genome/whole-exome DNA sequencing studies. Recent advances in genomics have led to the discovery of risk genes in several psychiatric disorders, including related conditions such as OCD, but to date, TTM and ED have remained understudied.

Developing a phenotype risk score for tic disorders in a large, clinical biobank

Tics are a common feature of early-onset neurodevelopmental disorders, characterized by involuntary and repetitive movements or sounds. Despite affecting up to 2% of children and having a genetic contribution, the underlying causes remain poorly understood. In this study, we leverage dense phenotype information to identify features (i.e., symptoms and comorbid diagnoses) of tic disorders within the context of a clinical biobank. Using de-identified electronic health records (EHRs), we identified individuals with tic disorder diagnosis codes. We performed a phenome-wide association study (PheWAS) to identify the EHR features enriched in tic cases versus controls (n = 1406 and 7030; respectively) and found highly comorbid neuropsychiatric phenotypes, including: obsessive-compulsive disorder, attention-deficit/hyperactivity disorder, autism spectrum disorder, and anxiety (p < 7.396 × 10-5). These features (among others) were then used to generate a phenotype risk score (PheRS) for tic disorder, which was applied across an independent set of 90,051 individuals. A gold standard set of tic disorder cases identified by an EHR algorithm and confirmed by clinician chart review was then used to validate the tic disorder PheRS; the tic disorder PheRS was significantly higher among clinician-validated tic cases versus non-cases (p = 4.787 × 10-151; β = 1.68; SE = 0.06). Our findings provide support for the use of large-scale medical databases to better understand phenotypically complex and underdiagnosed conditions, such as tic disorders.

Human mutations in high-confidence Tourette disorder genes affect sensorimotor behavior, reward learning, and striatal dopamine in mice

Tourette disorder (TD) is poorly understood, despite affecting 1/160 children. A lack of animal models possessing construct, face, and predictive validity hinders progress in the field. We used CRISPR/Cas9 genome editing to generate mice with mutations orthologous to human de novo variants in two high-confidence Tourette genes, CELSR3 and WWC1. Mice with human mutations in Celsr3 and Wwc1 exhibit cognitive and/or sensorimotor behavioral phenotypes consistent with TD. Sensorimotor gating deficits, as measured by acoustic prepulse inhibition, occur in both male and female Celsr3 TD models. Wwc1 mice show reduced prepulse inhibition only in females. Repetitive motor behaviors, common to Celsr3 mice and more pronounced in females, include vertical rearing and grooming. Sensorimotor gating deficits and rearing are attenuated by aripiprazole, a partial agonist at dopamine type II receptors. Unsupervised machine learning reveals numerous changes to spontaneous motor behavior and less predictable patterns of movement. Continuous fixed-ratio reinforcement shows that Celsr3 TD mice have enhanced motor responding and reward learning. Electrically evoked striatal dopamine release, tested in one model, is greater. Brain development is otherwise grossly normal without signs of striatal interneuron loss. Altogether, mice expressing human mutations in high-confidence TD genes exhibit face and predictive validity. Reduced prepulse inhibition and repetitive motor behaviors are core behavioral phenotypes and are responsive to aripiprazole. Enhanced reward learning and motor responding occur alongside greater evoked dopamine release. Phenotypes can also vary by sex and show stronger affection in females, an unexpected finding considering males are more frequently affected in TD.

The role of neuroactive steroids in tic disorders

Tics are sudden, repetitive movements or vocalizations. Tic disorders, such as Tourette syndrome (TS), are contributed by the interplay of genetic risk factors and environmental variables, leading to abnormalities in the functioning of the cortico-striatal-thalamo-cortical (CSTC) circuitry. Various neurotransmitter systems, such as gamma-aminobutyric acid (GABA) and dopamine, are implicated in the pathophysiology of these disorders. Building on the evidence that tic disorders are predominant in males and exacerbated by stress, emerging research is focusing on the involvement of neuroactive steroids, including dehydroepiandrosterone sulfate (DHEAS) and allopregnanolone, in the ontogeny of tics and other phenotypes associated with TS. Emerging evidence indicates that DHEAS levels are significantly elevated in the plasma of TS-affected boys, and the clinical onset of this disorder coincides with the period of adrenarche, the developmental stage characterized by a surge in DHEAS synthesis. On the other hand, allopregnanolone has garnered particular attention for its potential to mediate the adverse effects of acute stress on the exacerbation of tic severity and frequency. Notably, both neurosteroids act as key modulators of GABA-A receptors, suggesting a pivotal role of these targets in the pathophysiology of various clinical manifestations of tic disorders. This review explores the potential mechanisms by which these and other neuroactive steroids may influence tic disorders and discusses the emerging therapeutic strategies that target neuroactive steroids for the management of tic disorders.

Abnormal H3K4 enzyme catalytic activity and neuronal morphology caused by ASH1L mutations in individuals with Tourette syndrome

ASH1L potentially contributes to Tourette syndrome (TS) and other neuropsychiatric disorders, as our previous studies have shown. It regulates essential developmental genes by counteracting polycomb-mediated transcriptional repression, which restricts chromatin accessibility at target genes. ASH1L is highly expressed in the adult brain, playing a crucial role in the early stage. However, it remains unclear how ASH1L mutations carried by patients with TS participate in regulating neuronal growth processes leading to TS traits. Five TS families recruited in our study underwent comprehensive physical examinations and questionnaires to record clinical phenotypes and environmental impact factors. We validated the variants via Sanger sequencing and constructed two mutants near the catalytic domain of ASH1L. We conducted molecular modeling, in vitro assays, and primary neuron cultures to find the role of ASH1L in neuronal development and its correlation with TS. In this study, we validated five pathogenic ASH1L rare variants and observed symptoms in patients with simple tics and behavioral comorbidities. Mutations near the catalytic domain of TS patients cause mental state abnormalities and disrupt ASH1L function by destabilizing its spatial conformation, leading to decreased activity of catalytic H3K4, thereby affecting the neurite growth. We need to conduct larger-scale studies on TS patients and perform additional neurological evaluations on mature neurons. We first reported the effects of ASH1L mutations in TS patients, including phenotypic heterogeneity, protein function, and neurological growth. This information contributes to understanding the neurodevelopmental pathogenesis of TS in patients with ASH1L mutations.

Ash1L ameliorates psoriasis via limiting neuronal activity-dependent release of miR-let-7b

BACKGROUND AND PURPOSE

Psoriasis is a common autoimmune skin disease that significantly diminishes patients' quality of life. Interactions between primary afferents of the somatosensory system and the cutaneous immune system mediate the pathogenesis of psoriasis. This study aims to elucidate the molecular mechanisms of how primary sensory neurons regulate psoriasis formation.

EXPERIMENTAL APPROACH

Skin and total RNA were extracted from wild-type (WT) and ASH1-like histone lysine methyltransferase (Ash1l+/- ) mice in both naive and imiquimod (IMQ)-induced psoriasis models. Immunohistochemistry, quantitative real-time polymerase chain reaction (qRT-PCR) and fluorescence-activated cell sorting (FACS) were then performed. Microfluidic chamber coculture was used to investigate the interaction between somatosensory neurons and bone marrow dendritic cells (BMDCs) ex vivo. Whole-cell patch clamp recordings were used to evaluate neuronal excitability after Ash1L haploinsufficiency in primary sensory neurons.

KEY RESULTS

The haploinsufficiency of ASH1L, a histone methyltransferase, in primary sensory neurons causes both neurite hyperinnervation and increased neuronal excitability, which promote miR-let-7b release from primary afferents in the skin in a neuronal activity-dependent manner. With a 'GUUGUGU' core sequence, miR-let-7b functions as an endogenous ligand of toll-like receptor 7 (TLR7) and stimulates the activation of dermal dendritic cells (DCs) and interleukin (IL)-23/IL-17 axis, ultimately exacerbating the symptoms of psoriasis. Thus, by limiting miR-let-7b release from primary afferents, ASH1L prevents dermal DC activation and ameliorates psoriasis.

CONCLUSION AND IMPLICATIONS

Somatosensory neuron ASH1L modulates the cutaneous immune system by limiting neuronal activity-dependent release of miR-let-7b, which can directly activate dermal DCs via TLR7 and ultimately lead to aggravated psoriatic lesion.

Expansion of the Genotypic and Phenotypic Spectrum of ASH1L-Related Syndromic Neurodevelopmental Disorder

Pathogenic ASH1L variants have been reported in probands with broad phenotypic presentations, including intellectual disability, autism spectrum disorder, attention deficit hyperactivity disorder, seizures, congenital anomalies, and other skeletal, muscular, and sleep differences. Here, we review previously published individuals with pathogenic ASH1L variants and report three further probands with novel ASH1L variants and previously unreported phenotypic features, including mixed receptive language disorder and gait disturbances. These novel data from the Brain Gene Registry, an accessible repository of clinically derived genotypic and phenotypic data, have allowed for the expansion of the phenotypic and genotypic spectrum of this condition.

Human mutations in high-confidence Tourette disorder genes affect sensorimotor behavior, reward learning, and striatal dopamine in mice

Tourette disorder (TD) is poorly understood, despite affecting 1/160 children. A lack of animal models possessing construct, face, and predictive validity hinders progress in the field. We used CRISPR/Cas9 genome editing to generate mice with mutations orthologous to human de novo variants in two high-confidence Tourette genes, CELSR3 and WWC1 . Mice with human mutations in Celsr3 and Wwc1 exhibit cognitive and/or sensorimotor behavioral phenotypes consistent with TD. Sensorimotor gating deficits, as measured by acoustic prepulse inhibition, occur in both male and female Celsr3 TD models. Wwc1 mice show reduced prepulse inhibition only in females. Repetitive motor behaviors, common to Celsr3 mice and more pronounced in females, include vertical rearing and grooming. Sensorimotor gating deficits and rearing are attenuated by aripiprazole, a partial agonist at dopamine type II receptors. Unsupervised machine learning reveals numerous changes to spontaneous motor behavior and less predictable patterns of movement. Continuous fixed-ratio reinforcement shows Celsr3 TD mice have enhanced motor responding and reward learning. Electrically evoked striatal dopamine release, tested in one model, is greater. Brain development is otherwise grossly normal without signs of striatal interneuron loss. Altogether, mice expressing human mutations in high-confidence TD genes exhibit face and predictive validity. Reduced prepulse inhibition and repetitive motor behaviors are core behavioral phenotypes and are responsive to aripiprazole. Enhanced reward learning and motor responding occurs alongside greater evoked dopamine release. Phenotypes can also vary by sex and show stronger affection in females, an unexpected finding considering males are more frequently affected in TD.

Significance Statement

We generated mouse models that express mutations in high-confidence genes linked to Tourette disorder (TD). These models show sensorimotor and cognitive behavioral phenotypes resembling TD-like behaviors. Sensorimotor gating deficits and repetitive motor behaviors are attenuated by drugs that act on dopamine. Reward learning and striatal dopamine is enhanced. Brain development is grossly normal, including cortical layering and patterning of major axon tracts. Further, no signs of striatal interneuron loss are detected. Interestingly, behavioral phenotypes in affected females can be more pronounced than in males, despite male sex bias in the diagnosis of TD. These novel mouse models with construct, face, and predictive validity provide a new resource to study neural substrates that cause tics and related behavioral phenotypes in TD.

Diagnostic yield of prenatal exome sequencing in the genetic screening of fetuses with brain anomalies detected by MRI and ultrasonography: A systematic review and meta-analysis

BACKGROUND

Brain anomalies (BAs) have been the focus of research, as they have a high impact on fetal health but therapeutic and diagnostic approaches are limited.

OBJECTIVES

In this study, the application and efficiency of exome sequencing (ES) in detecting different cases of BAs in fetuses were evaluated and compared with chromosomal microarray analysis (CMA).

SEARCH STRATEGY

To conduct this study, three databases including PubMed, Web of Science and Embase were utilised with the keywords 'prenatal', 'diagnoses', 'brain anomalies' and 'exome sequencing'.

SELECTION CRITERIA

Studies were included based on the STARD checklist, for which the ES and CMA diagnostic yields were calculated.

DATA COLLECTION AND ANALYSIS

Meta-analysis was performed on the included studies using a random-effects model and subgroup analysis to define the risk difference between them.

MAIN RESULTS

We included 11 studies representing 779 fetuses that implemented ES along with imaging techniques. The pooled ES diagnostic yield in fetuses with BAs detected through magnetic resonance imaging (MRI) and ultrasonography was 26.53%, compared with 3.46% for CMA. The risk difference between ES and CMA for complex BAs was 0.36 [95% confidence interval (CI) 0.24-0.47], which was higher than for single BAs (0.22; 95% CI 0.18-0.25].

CONCLUSIONS

ES is a useful method with a significantly higher diagnostic yield than CMA for genetic assessment of fetuses with complex BAs detected by imaging techniques. Moreover, ES could be applied to suspected fetuses with related family histories to predict congenital diseases with high efficiency.

The role of histone methyltransferases in neurocognitive disorders associated with brain size abnormalities

Brain size is controlled by several factors during neuronal development, including neural progenitor proliferation, neuronal arborization, gliogenesis, cell death, and synaptogenesis. Multiple neurodevelopmental disorders have co-morbid brain size abnormalities, such as microcephaly and macrocephaly. Mutations in histone methyltransferases that modify histone H3 on Lysine 36 and Lysine 4 (H3K36 and H3K4) have been identified in neurodevelopmental disorders involving both microcephaly and macrocephaly. H3K36 and H3K4 methylation are both associated with transcriptional activation and are proposed to sterically hinder the repressive activity of the Polycomb Repressor Complex 2 (PRC2). During neuronal development, tri-methylation of H3K27 (H3K27me3) by PRC2 leads to genome wide transcriptional repression of genes that regulate cell fate transitions and neuronal arborization. Here we provide a review of neurodevelopmental processes and disorders associated with H3K36 and H3K4 histone methyltransferases, with emphasis on processes that contribute to brain size abnormalities. Additionally, we discuss how the counteracting activities of H3K36 and H3K4 modifying enzymes vs. PRC2 could contribute to brain size abnormalities which is an underexplored mechanism in relation to brain size control.

Molecular Landscape of Tourette's Disorder

Tourette's disorder (TD) is a highly heritable childhood-onset neurodevelopmental disorder and is caused by a complex interplay of multiple genetic and environmental factors. Yet, the molecular mechanisms underlying the disorder remain largely elusive. In this study, we used the available omics data to compile a list of TD candidate genes, and we subsequently conducted tissue/cell type specificity and functional enrichment analyses of this list. Using genomic data, we also investigated genetic sharing between TD and blood and cerebrospinal fluid (CSF) metabolite levels. Lastly, we built a molecular landscape of TD through integrating the results from these analyses with an extensive literature search to identify the interactions between the TD candidate genes/proteins and metabolites. We found evidence for an enriched expression of the TD candidate genes in four brain regions and the pituitary. The functional enrichment analyses implicated two pathways ('cAMP-mediated signaling' and 'Endocannabinoid Neuronal Synapse Pathway') and multiple biological functions related to brain development and synaptic transmission in TD etiology. Furthermore, we found genetic sharing between TD and the blood and CSF levels of 39 metabolites. The landscape of TD not only provides insights into the (altered) molecular processes that underlie the disease but, through the identification of potential drug targets (such as FLT3, NAALAD2, CX3CL1-CX3CR1, OPRM1, and HRH2), it also yields clues for developing novel TD treatments.

Emerging therapies and recent advances for Tourette syndrome

Tourette syndrome is the most prevalent hyperkinetic movement disorder in children and can be highly disabling. While the pathomechanism of Tourette syndrome remains largely obscure, recent studies have greatly improved our knowledge about this disease, providing a new perspective in our understanding of this condition. Advances in electrophysiology and neuroimaging have elucidated that there is a reduction in frontal cortical volume and reduction of long rage connectivity to the frontal lobe from other parts of the brain. Several genes have also been identified to be associated with Tourette syndrome. Treatment of Tourette syndrome requires a multidisciplinary approach which includes behavioral and pharmacological therapy. In severe cases surgical therapy with deep brain stimulation may be warranted, though the optimal location for stimulation is still being investigated. Studies on alternative therapies including traditional Chinese medicine and neuromodulation, such as transcranial magnetic stimulation have shown promising results, but still are being used in an experimental basis. Several new therapies have also recently been tested in clinical trials. This review provides an overview of the latest findings with regards to genetics and neuroimaging for Tourette syndrome as well as an update on advanced therapeutics.

Identity-by-descent analysis of a large Tourette's syndrome pedigree from Costa Rica implicates genes involved in neuronal development and signal transduction

Tourette Syndrome (TS) is a heritable, early-onset neuropsychiatric disorder that typically begins in early childhood. Identifying rare genetic variants that make a significant contribution to risk in affected families may provide important insights into the molecular aetiology of this complex and heterogeneous syndrome. Here we present a whole-genome sequencing (WGS) analysis from the 11-generation pedigree (>500 individuals) of a densely affected Costa Rican family which shares ancestry from six founder pairs. By conducting an identity-by-descent (IBD) analysis using WGS data from 19 individuals from the extended pedigree we have identified putative risk haplotypes that were not seen in controls, and can be linked with four of the six founder pairs. Rare coding and non-coding variants present on the haplotypes and only seen in haplotype carriers show an enrichment in pathways such as regulation of locomotion and signal transduction, suggesting common mechanisms by which the haplotype-specific variants may be contributing to TS-risk in this pedigree. In particular we have identified a rare deleterious missense variation in RAPGEF1 on a chromosome 9 haplotype and two ultra-rare deleterious intronic variants in ERBB4 and IKZF2 on the same chromosome 2 haplotype. All three genes play a role in neurodevelopment. This study, using WGS data in a pedigree-based approach, shows the importance of investigating both coding and non-coding variants to identify genes that may contribute to disease risk. Together, the genes and variants identified on the IBD haplotypes represent biologically relevant targets for investigation in other pedigree and population-based TS data.

Structural insight into ASH1L PHD finger recognizing methylated histone H3K4 and promoting cell growth in prostate cancer

ASH1L is a member of the Trithorax-group protein and acts as a histone methyltransferase for gene transcription activation. It is known that ASH1L modulates H3K4me3 and H3K36me2/3 at its gene targets, but its specific mechanism of histone recognition is insufficiently understood. In this study, we found that the ASH1L plant homeodomain (PHD) finger interacts with mono-, di-, and trimethylated states of H3K4 peptides with comparable affinities, indicating that ASH1L PHD non-selectively binds to all three methylation states of H3K4. We solved nuclear magnetic resonance structures picturing the ASH1L PHD finger binding to the dimethylated H3K4 peptide and found that a narrow binding groove and residue composition in the methylated-lysine binding pocket restricts the necessary interaction with the dimethyl-ammonium moiety of K4. In addition, we found that the ASH1L protein is overexpressed in castrate-resistant prostate cancer (PCa) PC3 and DU145 cells in comparison to PCa LNCaP cells. The knockdown of ASH1L modulated gene expression and cellular pathways involved in apoptosis and cell cycle regulation and consequently induced cell cycle arrest, cell apoptosis, and reduced colony-forming abilities in PC3 and DU145 cells. The overexpression of the C-terminal core of ASH1L but not the PHD deletion mutant increased the overall H3K36me2 level but had no effect on the H3K4me2/3 level. Overall, our study identifies the ASH1L PHD finger as the first native reader that non-selectively recognizes the three methylation states of H3K4. Additionally, ASH1L is required for the deregulation of cell cycle and survival in PCas.

Mitochondrial DNA variants spectrum and the association with chronic Tic disorders

BACKGROUND

Tic disorders (TD) are childhood-onset neuropsychiatric disorders characterized by single or multiple sudden, rapid, recurrent, and motor tics and/or vocal tics. Several nuclear genes that involved in mitochondrial functions suggest potential role of mitochondria in tic deficit.

METHODS

To evaluate the association of mitochondrial DNA (mtDNA) variants with Tic disorders, we screened the whole mitochondrial genomes in 493 TD patients and 109 age- and sex matched healthy controls using next-generation sequencing technology.

RESULTS

A total of 1918 mtDNA variants including 1220 variants in patients only, 154 variants in controls only, and 544 variants shared by both cases and controls were identified. We found higher number of overall mtDNA variants in TD patients (P =0.00028). The variant density in MT-ATP6/8 and MT-CYB coding regions had significant difference between TD patients and controls (P=0.0025 and P=0.003, respectively). Furthermore, we observed a significant association of 15 common variants with TD based on additive model, including m.14766C>T, m.14783T>C, m.14905G>A, and m.15301G>A in MT-CYB; m.4769A>G, m.10398A>G, m.12705C>T, and m.12850A>G in MT-ND genes; m.7028C>T in MT-CO1; m.8701A>G in MT-ATP6; two noncoding variants with m.16223C>T, m.5580T>C; and three rRNA variants with m.1438A>G and m.750A>G in RNR1, and m.2352T>C in RNR2.

CONCLUSIONS

Our data provide the evidence of mtDNA variants associated with tic disorders. The accumulation of the heteroplasmic levels may increase the risk of TD. Replication studies with larger samples are necessary to understand the pathogenesis of TD.

ASH1L may contribute to the risk of Tourette syndrome: Combination of family-based analysis and case-control study

OBJECTIVE

Tourette syndrome (TS) is a childhood neurodevelopmental disorder caused by various genetic and environmental factors and presents with apparent genetic heterogeneity. As ASH1L potentially contributes to neurodevelopmental diseases, especially in TS, we aim to investigate the susceptibility of ASH1L on TS in the Chinese Han population.

METHODS

Three tag single nucleotide polymorphisms (SNPs) (rs5005770, rs12734374, and rs35615695) in ASH1L were screened in 271 TS nuclear family trios and 337 healthy subjects by the TaqMan assays real time. A case-control study combined with family-based analysis was applied to study the genetic susceptibility of common variants of ASH1L.

RESULTS

The results revealed a significant over-transmission of rs35615695 and rs5005770 (for rs35615695, transmission disequilibrium test, χ²  = 57.375, p = .000, HHRR, χ²  = 4.807, p = .028; for rs5005770, HRR, χ²  = 4.116, p = .042, HHRR, χ²  = 8.223, p = .004) in family-based study. Furthermore, rs5005770 and rs35615695 still remained significant after Bonferroni correction (p < .017). However, the two SNPs (rs5005770 and rs35615695) were found not to be associated with TS in case-control study.

CONCLUSIONS

Our study suggests that ASH1L may contribute to TS susceptibility in the Han Chinese population and involved in TS development as a risk factor.

Role of histidine decarboxylase gene in the pathogenesis of Tourette syndrome

Tourette syndrome (TS) is caused by complex genetic and environmental factors and is characterized by tics. Histidine decarboxylase (HDC) mutation is a rare genetic cause with high penetrance in patients with TS. HDC-knockout (KO) mice have similar behavioral and neurochemical abnormalities as patients with TS. Therefore, HDC-KO mice are considered a valuable TS pathophysiological model as it reveals the underlying pathological mechanisms that cannot be obtained from patients with TS, thus advancing the development of treatment strategies for TS and other tic disorders. This review summarizes some of the recent research hotspots and progress in HDC-KO mice, aiming to deepen our understanding of brain mechanisms relevant to TS. Furthermore, we encapsulate the possible brain nerve cell changes in HDC-KO mice and their potential roles in TS to provide multiple directions for the future research on tics.

Current Understanding of the Genetics of Tourette Syndrome

Gilles de la Tourette syndrome (TS) is a common, childhood-onset psychiatric disorder characterized by persistent motor and vocal tics. It is a heterogeneous disorder in which the phenotypic expression may be affected by environmental factors, such as immune responses. Furthermore, several studies have shown that genetic factors play a vital role in the etiology of TS, as well as its comorbidity with other disorders, including attention deficit hyperactivity disorder, obsessive-compulsive disorder, and autism spectrum disorder. TS has a complex inheritance pattern and, according to various genetic studies, several genes and loci have been correlated with TS. Genome-wide linkage studies have identified Slit and Trk-like 1 (SLITRK1) and histidine decarboxylase (HDC) genes, and candidate gene association studies have extensively investigated the dopamine and serotonin system genes, but there have been no consistent results. Moreover, genome-wide association studies have implicated several genetic loci; however, larger study cohorts are needed to confirm this. Copy number variations, which are polymorphisms in the number of gene copies due to chromosomal deletions or duplications, are considered another significant source of mutations in TS. In the last decade, whole genome/exome sequencing has identified several novel genetic mutations in patients with TS. In conclusion, more studies are needed to reveal the exact mechanisms of underlying TS, which may help to provide more information on the prognosis and therapeutic plans for TS.

Enhancing neuroimaging genetics through meta-analysis for Tourette syndrome (ENIGMA-TS): A worldwide platform for collaboration

Tourette syndrome (TS) is characterized by multiple motor and vocal tics, and high-comorbidity rates with other neuropsychiatric disorders. Obsessive compulsive disorder (OCD), attention deficit hyperactivity disorder (ADHD), autism spectrum disorders (ASDs), major depressive disorder (MDD), and anxiety disorders (AXDs) are among the most prevalent TS comorbidities. To date, studies on TS brain structure and function have been limited in size with efforts mostly fragmented. This leads to low-statistical power, discordant results due to differences in approaches, and hinders the ability to stratify patients according to clinical parameters and investigate comorbidity patterns. Here, we present the scientific premise, perspectives, and key goals that have motivated the establishment of the Enhancing Neuroimaging Genetics through Meta-Analysis for TS (ENIGMA-TS) working group. The ENIGMA-TS working group is an international collaborative effort bringing together a large network of investigators who aim to understand brain structure and function in TS and dissect the underlying neurobiology that leads to observed comorbidity patterns and clinical heterogeneity. Previously collected TS neuroimaging data will be analyzed jointly and integrated with TS genomic data, as well as equivalently large and already existing studies of highly comorbid OCD, ADHD, ASD, MDD, and AXD. Our work highlights the power of collaborative efforts and transdiagnostic approaches, and points to the existence of different TS subtypes. ENIGMA-TS will offer large-scale, high-powered studies that will lead to important insights toward understanding brain structure and function and genetic effects in TS and related disorders, and the identification of biomarkers that could help inform improved clinical practice.

Rare variants in the outcome of social skills group training for autism

Exome sequencing has been proposed as the first-tier genetic testing in autism spectrum disorder (ASD). Here, we performed exome sequencing in autistic individuals with average to high intellectual abilities (N = 207) to identify molecular diagnoses and genetic modifiers of intervention outcomes of social skills group training (SSGT) or standard care. We prioritized variants of clinical significance (VCS), variants of uncertain significance (VUS) and generated a pilot scheme to calculate genetic scores of rare and common variants in ASD-related gene pathways. Mixed linear models were used to test the association between the carrier status of VCS/VUS or the genetic scores with intervention outcomes measured by the social responsiveness scale. Additionally, we combined behavioral and genetic features using a machine learning (ML) model to predict the individual response. We showed a rate of 4.4% and 11.3% of VCS and VUS in the cohort, respectively. Individuals with VCS or VUS had improved significantly less after standard care than non-carriers at post-intervention (β = 9.35; p = 0.036), while no such association was observed for SSGT (β = -2.50; p = 0.65). Higher rare variant genetic scores for synaptic transmission and regulation of transcription from RNA polymerase II were separately associated with less beneficial (β = 8.30, p = 0.0044) or more beneficial (β = -6.79, p = 0.014) effects after SSGT compared with standard care at follow-up, respectively. Our ML model showed the importance of rare variants for outcome prediction. Further studies are needed to understand genetic predisposition to intervention outcomes in ASD.

Effects of Chemogenetic Inhibition of D1 or D2 Receptor-Containing Neurons of the Substantia Nigra and Striatum in Mice With Tourette Syndrome

As tourette syndrome (TS) is a common neurobehavioral disorder, the primary symptoms of which include behavioral stereotypies. Dysfunction of the substantia nigra-striatum network could be the main pathogenesis of TS, which is closely associated with dopamine (DA) and its receptors. TS is often resistant to conventional treatments. Therefore, it is necessary to investigate the neurobiological mechanisms underlying its pathogenesis. In this study, we investigated whether chemogenetic activation or inhibition of dopaminergic D1 receptor (D1R)- or D2 receptor (D2R)-containing neurons in the substantia nigra pars compacta (SNpc) or dorsal striatum (dSTR) affected the stereotyped behavior and motor functions of TS mice. Intraperitoneal injection of 3,3'-iminodipropionitrile (IDPN) was used to induce TS in mice. Stereotyped behavior test and open-field, rotarod, and grip strength tests were performed to evaluate stereotyped behavior and motor functions, respectively. Immunofluorescence labeling was used to detect the co-labeling of virus fluorescence and D1R or D2R. We found that chemogenetic inhibition of D1R- or D2R-containing neurons in the SNpc and dSTR alleviated behavioral stereotypies and motor functions in TS mice. Chemogenetic activation of D1R-containing neurons in the dSTR aggravated behavioral stereotypies and motor functions in vehicle-treated mice, but neither was aggravated in TS mice. In conclusion, chemogenetic inhibition of D1R- or D2R-containing neurons in the SNpc and dSTR alleviated behavioral stereotypies of TS, providing a new treatment target for TS. Moreover, the activation of D1R-containing neurons in the dSTR may contribute to the pathogenesis of TS, which can be chosen as a more precise target for treatment.

Deficiency of autism risk factor ASH1L in prefrontal cortex induces epigenetic aberrations and seizures

ASH1L, a histone methyltransferase, is identified as a top-ranking risk factor for autism spectrum disorder (ASD), however, little is known about the biological mechanisms underlying the link of ASH1L haploinsufficiency to ASD. Here we show that ASH1L expression and H3K4me3 level are significantly decreased in the prefrontal cortex (PFC) of postmortem tissues from ASD patients. Knockdown of Ash1L in PFC of juvenile mice induces the downregulation of risk genes associated with ASD, intellectual disability (ID) and epilepsy. These downregulated genes are enriched in excitatory and inhibitory synaptic function and have decreased H3K4me3 occupancy at their promoters. Furthermore, Ash1L deficiency in PFC causes the diminished GABAergic inhibition, enhanced glutamatergic transmission, and elevated PFC pyramidal neuronal excitability, which is associated with severe seizures and early mortality. Chemogenetic inhibition of PFC pyramidal neuronal activity, combined with the administration of GABA enhancer diazepam, rescues PFC synaptic imbalance and seizures, but not autistic social deficits or anxiety-like behaviors. These results have revealed the critical role of ASH1L in regulating synaptic gene expression and seizures, which provides insights into treatment strategies for ASH1L-associated brain diseases.

Genetic architecture of Tourette syndrome: our current understanding

Tourette syndrome (TS) is a severe neuropsychiatric disorder characterized by recurrent, involuntary physical and verbal tics. With a prevalence as high as 1% in children, a deeper understanding of the etiology of the disorder and contributions to risk is critical. Here, we cover the current body of knowledge in scientific literature regarding the genetics of TS. We first review the history and diagnostic criteria for TS cases. We then cover the prevalence, and begin to address the etiology of the disorder. We highlight long-standing evidence for a genetic contribution to TS risk from epidemiology studies focused on twins, families, and population-scale data. Finally, we summarize current large-scale genetic studies of TS along specific classes of genetic variation, including common variation, rare copy number variation, and de novo variation that impact protein-coding sequence. Although these variants do not account for the entirety of TS genetic risk, current evidence is clear that each class of variation is a factor in the overall risk architecture across TS cases.

Recent progress on Tourette syndrome

Tic disorders and Tourette syndrome are the most common movement disorders in children and are characterized by movements or vocalizations. Clinically, Tourette syndrome is frequently associated with comorbid psychiatric symptoms. Although dysfunction of cortical–striatal–thalamic–cortical circuits with aberrant neurotransmitter function has been considered the proximate cause of tics, the mechanism underlying this association is unclear. Recently, many studies have been conducted to elucidate the epidemiology, clinical course, comorbid symptoms, and pathophysiology of tic disorders by using laboratory studies, neuroimaging, electrophysiological testing, environmental exposure, and genetic testing. In addition, many researchers have focused on treatment for tics, including behavioral therapy, pharmacological treatment, and surgical treatment. Here, we provide an overview of recent progress on Tourette syndrome.

Candidate Genes and Pathways Associated with Gilles de la Tourette Syndrome-Where Are We?

Gilles de la Tourette syndrome (GTS) is a childhood-onset neurodevelopmental and -psychiatric tic-disorder of complex etiology which is often comorbid with obsessive-compulsive disorder (OCD) and/or attention deficit hyperactivity disorder (ADHD). Twin and family studies of GTS individuals have shown a high level of heritability suggesting, that genetic risk factors play an important role in disease etiology. However, the identification of major GTS susceptibility genes has been challenging, presumably due to the complex interplay between several genetic factors and environmental influences, low penetrance of each individual factor, genetic diversity in populations, and the presence of comorbid disorders. To understand the genetic components of GTS etiopathology, we conducted an extensive review of the literature, compiling the candidate susceptibility genes identified through various genetic approaches. Even though several strong candidate genes have hitherto been identified, none of these have turned out to be major susceptibility genes yet.

A Comprehensive Review of Tic Disorders in Children

Tics are characterized by sudden, rapid, recurrent, nonrhythmic movement or vocalization, and are the most common movement disorders in children. Their onset is usually in childhood and tics often will diminish within one year. However, some of the tics can persist and cause various problems such as social embarrassment, physical discomfort, or emotional impairments, which could interfere with daily activities and school performance. Furthermore, tic disorders are frequently associated with comorbid neuropsychiatric symptoms, which can become more problematic than tic symptoms. Unfortunately, misunderstanding and misconceptions of tic disorders still exist among the general population. Understanding tic disorders and their comorbidities is important to deliver appropriate care to patients with tics. Several studies have been conducted to elucidate the clinical course, epidemiology, and pathophysiology of tics, but they are still not well understood. This article aims to provide an overview about tics and tic disorders, and recent findings on tic disorders including history, definition, diagnosis, epidemiology, etiology, diagnostic approach, comorbidities, treatment and management, and differential diagnosis.

Sex-Specific Transcriptional Changes in Response to Adolescent Social Stress in the Brain's Reward Circuitry

BACKGROUND

Sex differences in addiction have been described in humans and animal models. A key factor that influences addiction in both males and females is adolescent experience. Adolescence is associated with higher vulnerability to substance use disorders, and male rodents subjected to adolescent social isolation (SI) stress form stronger preferences for drugs of abuse in adulthood. However, little is known about how females respond to SI, and few studies have investigated the transcriptional changes induced by SI in the brain's reward circuitry.

METHODS

We tested the hypothesis that SI alters the transcriptome in a persistent and sex-specific manner in prefrontal cortex, nucleus accumbens, and ventral tegmental area. Mice were isolated or group housed from postnatal day P22 to P42, then group housed until ∼P90. Transcriptome-wide changes were investigated by RNA sequencing after acute or chronic cocaine or saline administration.

RESULTS

We found that SI disrupts sex-specific transcriptional responses to cocaine and reduces sex differences in gene expression across all three brain regions. Furthermore, SI induces gene expression profiles in males that more closely resemble group-housed females, suggesting that SI "feminizes" the male transcriptome. Coexpression analysis reveals that such disruption of sex differences in gene expression alters sex-specific gene networks and identifies potential sex-specific key drivers of these transcriptional changes.

CONCLUSIONS

Together, these data show that SI has region-specific effects on sex-specific transcriptional responses to cocaine and provide a better understanding of reward-associated transcription that differs in males and females.

Role of Ash1l in Tourette syndrome and other neurodevelopmental disorders

Ash1l potentially contributes to neurodevelopmental diseases. Although specific Ash1l mutations are rare, they have led to informative studies in animal models that may bring therapeutic advances. Ash1l is highly expressed in the brain and correlates with the neuropathology of Tourette syndrome (TS), autism spectrum disorder, and intellectual disability during development, implicating shared epigenetic factors and overlapping neuropathological mechanisms. Functional convergence of Ash1l generated several significant signaling pathways: chromatin remodeling and transcriptional regulation, protein synthesis and cellular metabolism, and synapse development and function. Here, we systematically review the literature on Ash1l, including its discovery, expression, function, regulation, implication in the nervous system, signaling pathway, mutations, and putative involvement in TS and other neurodevelopmental traits. Such findings highlight Ash1l pleiotropy and the necessity of transcending a single gene to complicated mechanisms of network convergence underlying these diseases. With the progress in functional genomic analysis (highlighted in this review), and although the importance and necessity of Ash1l becomes increasingly apparent in the medical field, further research is required to discover the precise function and molecular regulatory mechanisms related to Ash1l. Thus, a new perspective is proposed for basic scientific research and clinical interventions for cross‐disorder diseases.

Tourette syndrome research highlights from 2019

This is the sixth yearly article in the Tourette Syndrome Research Highlights series, summarizing research from 2019 relevant to Tourette syndrome and other tic disorders. The highlights from 2020 is being drafted on the Authorea online authoring platform; readers are encouraged to add references or give feedback on our selections comments feature on this page. After the calendar year ends, this article is submitted as the annual update for the Tics collection F1000Research.

GPCR-Based Dopamine Sensors-A Detailed Guide to Inform Sensor Choice for In vivo Imaging

Understanding how dopamine (DA) encodes behavior depends on technologies that can reliably monitor DA release in freely-behaving animals. Recently, red and green genetically encoded sensors for DA (dLight, GRAB-DA) were developed and now provide the ability to track release dynamics at a subsecond resolution, with submicromolar affinity and high molecular specificity. Combined with rapid developments in in vivo imaging, these sensors have the potential to transform the field of DA sensing and DA-based drug discovery. When implementing these tools in the laboratory, it is important to consider there is not a 'one-size-fits-all' sensor. Sensor properties, most importantly their affinity and dynamic range, must be carefully chosen to match local DA levels. Molecular specificity, sensor kinetics, spectral properties, brightness, sensor scaffold and pharmacology can further influence sensor choice depending on the experimental question. In this review, we use DA as an example; we briefly summarize old and new techniques to monitor DA release, including DA biosensors. We then outline a map of DA heterogeneity across the brain and provide a guide for optimal sensor choice and implementation based on local DA levels and other experimental parameters. Altogether this review should act as a tool to guide DA sensor choice for end-users.