De novo loss-of-function variants of ASH1L are associated with an emergent neurodevelopmental disorder

Combining Off-flow, a Nextflow-coded program, and whole genome sequencing reveals unintended genetic variation in CRISPR/Cas-edited iPSCs

Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-Cas nucleases and human induced pluripotent stem cell (iPSC) technology can reveal deep insight into the genetic and molecular bases of human biology and disease. Undesired editing outcomes, both on-target (at the edited locus) and off-target (at other genomic loci) hinder the application of CRISPR-Cas nucleases. We developed Off-flow, a Nextflow-coded bioinformatic workflow that takes a specific guide sequence and Cas protein input to call four separate off-target prediction programs (CHOPCHOP, Cas-Offinder, CRISPRitz, CRISPR-Offinder) to output a comprehensive list of predicted off-target sites. We applied it to whole genome sequencing (WGS) data to investigate the occurrence of unintended effects in human iPSCs that underwent repair or insertion of disease-related variants by homology-directed repair. Off-flow identified a 3-base-pair-substitution and a mono-allelic genomic deletion at the target loci, KCNQ2, in 2 clones. Unbiased WGS analysis further identified off-target missense variants and a mono-allelic genomic deletion at the targeted locus, GNAQ, in 10 clones. On-target substitution and deletions had escaped standard PCR and Sanger sequencing analysis, while missense variants at other genomic loci were not detected by Off-flow. We used these results to filter out iPSC clones for subsequent functional experiments. Off-flow, which we make publicly available, works for human and mouse genomes currently and can be adapted for other genomes. Off-flow and WGS analysis can improve the integrity of studies using CRISPR/Cas-edited cells and animal models.

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.

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.

Genetic architecture of ADHD and overlap with other psychiatric disorders and cognition-related phenotypes

Attention-deficit/hyperactivity disorder (ADHD) co-occurs with many other psychiatric disorders and traits. In this review, we summarize and interpret the existing literature on the genetic architecture of these comorbidities based on hypothesis-generating approaches. Quantitative genetic studies indicate that genetic factors play a substantial role in the observed co-occurrence of ADHD with many different disorders and traits. Molecular genetic correlations derived from genome-wide association studies and results of studies based on polygenic risk scores confirm the general pattern but provide effect estimates that are smaller than those from twin studies. The identification of the specific genetic variants and biological pathways underlying co-occurrence using genome-wide approaches is still in its infancy. The first analyses of causal inference using genetic data support causal relationships between ADHD and comorbid disorders, although bidirectional effects identified in some instances point to complex relationships. While several issues in the methodology and inferences from the results are still to be overcome, this review shows that the co-occurrence of ADHD with many psychiatric disorders and traits is genetically interpretable.

ASH1L-MRG15 methyltransferase deposits H3K4me3 and FACT for damage verification in nucleotide excision repair

To recognize DNA adducts, nucleotide excision repair (NER) deploys the XPC sensor, which detects damage-induced helical distortions, followed by engagement of TFIIH for lesion verification. Accessory players ensure that this factor handover takes place in chromatin where DNA is tightly wrapped around histones. Here, we describe how the histone methyltransferase ASH1L, once activated by MRG15, helps XPC and TFIIH to navigate through chromatin and induce global-genome NER hotspots. Upon UV irradiation, ASH1L adds H3K4me3 all over the genome (except in active gene promoters), thus priming chromatin for XPC relocations from native to damaged DNA. The ASH1L-MRG15 complex further recruits the histone chaperone FACT to DNA lesions. In the absence of ASH1L, MRG15 or FACT, XPC is misplaced and persists on damaged DNA without being able to deliver the lesions to TFIIH. We conclude that ASH1L-MRG15 makes damage verifiable by the NER machinery through the sequential deposition of H3K4me3 and FACT.

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.

Identification of a transcriptional signature found in multiple models of ASD and related disorders

Epigenetic regulation plays a critical role in many neurodevelopmental disorders (NDDs), including autism spectrum disorder (ASD). In particular, many such disorders are the result of mutations in genes that encode chromatin-modifying proteins. However, although these disorders share many features, it is unclear whether they also share gene expression disruptions resulting from the aberrant regulation of chromatin. We examined five chromatin modifiers that are all linked to ASD despite their different roles in regulating chromatin. Specifically, we depleted ASH1L, CHD8, CREBBP, EHMT1, and NSD1 in parallel in a highly controlled neuronal culture system. We then identified sets of shared genes, or transcriptional signatures, that are differentially expressed following loss of multiple ASD-linked chromatin modifiers. We examined the functions of genes within the transcriptional signatures and found an enrichment in many neurotransmitter transport genes and activity-dependent genes. In addition, these genes are enriched for specific chromatin features such as bivalent domains that allow for highly dynamic regulation of gene expression. The down-regulated transcriptional signature is also observed within multiple mouse models of NDDs that result in ASD, but not those only associated with intellectual disability. Finally, the down-regulated transcriptional signature can distinguish between control and idiopathic ASD patient iPSC-derived neurons as well as postmortem tissue, demonstrating that this gene set is relevant to the human disorder. This work identifies a transcriptional signature that is found within many neurodevelopmental syndromes, helping to elucidate the link between epigenetic regulation and the underlying cellular mechanisms that result in ASD.

Structural and functional specificity of H3K36 methylation

The methylation of histone H3 at lysine 36 (H3K36me) is essential for maintaining genomic stability. Indeed, this methylation mark is essential for proper transcription, recombination, and DNA damage response. Loss- and gain-of-function mutations in H3K36 methyltransferases are closely linked to human developmental disorders and various cancers. Structural analyses suggest that nucleosomal components such as the linker DNA and a hydrophobic patch constituted by histone H2A and H3 are likely determinants of H3K36 methylation in addition to the histone H3 tail, which encompasses H3K36 and the catalytic SET domain. Interaction of H3K36 methyltransferases with the nucleosome collaborates with regulation of their auto-inhibitory changes fine-tunes the precision of H3K36me in mediating dimethylation by NSD2 and NSD3 as well as trimethylation by Set2/SETD2. The identification of specific structural features and various cis-acting factors that bind to different forms of H3K36me, particularly the di-(H3K36me2) and tri-(H3K36me3) methylated forms of H3K36, have highlighted the intricacy of H3K36me functional significance. Here, we consolidate these findings and offer structural insight to the regulation of H3K36me2 to H3K36me3 conversion. We also discuss the mechanisms that underlie the cooperation between H3K36me and other chromatin modifications (in particular, H3K27me3, H3 acetylation, DNA methylation and N⁶-methyladenosine in RNAs) in the physiological regulation of the epigenomic functions of chromatin.

Lysine methyltransferase inhibitors: where we are now

Protein lysine methyltransferases constitute a large family of epigenetic writers that catalyse the transfer of a methyl group from the cofactor S-adenosyl-l-methionine to histone- and non-histone-specific substrates. Alterations in the expression and activity of these proteins have been linked to the genesis and progress of several diseases, including cancer, neurological disorders, and growing defects, hence they represent interesting targets for new therapeutic approaches. Over the past two decades, the identification of modulators of lysine methyltransferases has increased tremendously, clarifying the role of these proteins in different physio-pathological states. The aim of this review is to furnish an updated outlook about the protein lysine methyltransferases disclosed modulators, reporting their potency, their mechanism of action and their eventual use in clinical and preclinical studies.

Neural Hyperactivity Is a Core Pathophysiological Change Induced by Deletion of a High Autism Risk Gene Ash1L in the Mouse Brain

ASH1L is one of the highest risk genes associated with autism spectrum disorder (ASD) and intellectual disability (ID). Our recent studies demonstrate that loss of Ash1l in the mouse brain is sufficient to induce ASD/ID-like behavioral and cognitive deficits, suggesting that disruptive ASH1L mutations are likely to have a positive correlation with ASD/ID genesis. However, the core pathophysiological changes in the Ash1l-deficient brain remain largely unknown. Here we show that loss of Ash1l in the mouse brain causes locomotor hyperactivity, high metabolic activity, and hyperactivity-related disturbed sleep and lipid metabolic changes. In addition, the mutant mice display lower thresholds for the convulsant reagent-induced epilepsy and increased neuronal activities in multiple brain regions. Thus, our current study reveals that neural hyperactivity is a core pathophysiological change in the Ash1l-deficient mouse brain, which may function as a brain-level mechanism leading to the Ash1l-deletion-induced brain functional abnormalities and autistic-like behavioral deficits.

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.

Counteracting epigenetic mechanisms regulate the structural development of neuronal circuitry in human neurons

Autism spectrum disorders (ASD) are associated with defects in neuronal connectivity and are highly heritable. Genetic findings suggest that there is an overrepresentation of chromatin regulatory genes among the genes associated with ASD. ASH1 like histone lysine methyltransferase (ASH1L) was identified as a major risk factor for ASD. ASH1L methylates Histone H3 on Lysine 36, which is proposed to result primarily in transcriptional activation. However, how mutations in ASH1L lead to deficits in neuronal connectivity associated with ASD pathogenesis is not known. We report that ASH1L regulates neuronal morphogenesis by counteracting the catalytic activity of Polycomb Repressive complex 2 group (PRC2) in stem cell-derived human neurons. Depletion of ASH1L decreases neurite outgrowth and decreases expression of the gene encoding the neurotrophin receptor TrkB whose signaling pathway is linked to neuronal morphogenesis. The neuronal morphogenesis defect is overcome by inhibition of PRC2 activity, indicating that a balance between the Trithorax group protein ASH1L and PRC2 activity determines neuronal morphology. Thus, our work suggests that ASH1L may epigenetically regulate neuronal morphogenesis by modulating pathways like the BDNF-TrkB signaling pathway. Defects in neuronal morphogenesis could potentially impair the establishment of neuronal connections which could contribute to the neurodevelopmental pathogenesis associated with ASD in patients with ASH1L mutations.

Genetic and Epigenetic Alterations in Autism Spectrum Disorder

It is extremely important to understand the causes of autism spectrum disorder (ASD) which is a neurodevelopmental disease. Treatment and lifelong support of autism are also important to improve the patient's life quality. In this article, several findings were explained to understand the possible causes of ASD. We draw, outline, and describe ASD and its relation with the epigenetic mechanisms. Here, we discuss, several different factors leading to ASD such as environmental, epigenetic, and genetic factors.

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.

Vorinostat, a histone deacetylase inhibitor, ameliorates the sociability and cognitive memory in an Ash1L-deletion-induced ASD/ID mouse model

Autism spectrum disorder (ASD) and intellectual disability (ID) are neurodevelopmental diseases associated with various gene mutations. Previous genetic and clinical studies reported that ASH1L is a high ASD risk gene identified in human patients. Our recent study used a mouse model to demonstrate that loss of ASH1L in the developing mouse brain was sufficient to cause multiple developmental defects, core autistic-like behaviors, and impaired cognitive memory, suggesting that the disruptive ASH1L mutations are the causative drivers leading the human ASD/ID genesis. Using this Ash1L-deletion-induced ASD/ID mouse model, here we showed that postnatal administration of vorinostat (SAHA), a histone deacetylase inhibitor (HDACi), significantly ameliorated both ASD-like behaviors and ID-like cognitive memory deficit. Thus, our study demonstrates that SAHA is a promising reagent for the pharmacological treatment of core ASD/ID behavioral and memory deficits caused by disruptive ASH1L mutations.

ASH1L mutation caused seizures and intellectual disability in twin sisters

ASH1L mutations have been identified with variable phenotypes, including intellectual disability, autism spectrum disorder (ASD), and multiple congenital anomalies (MCA). However, the mechanisms underlying this phenotypic variation remain unknown. Here, we present twin sisters exhibiting mild intellectual disability and seizures. Whole-exome sequencing of the family revealed a novel de novo heterozygous sequence variant, NM_018489.2: c.2678dup (p.Lys894*) in exon 3 of ASH1L which was estimated to be pathogenic. Furthermore, we reviewed previously reported ASH1L mutations in order to evaluate genotype-phenotype correlations for ASH1L variants. We found that patients with missense mutations in ASH1L appeared to present with more severe phenotypes and a higher likelihood of ASD than those with truncating mutations. The relationship between phenotype and genotype reported across several patients may help to explain the mechanisms underlying the phenotypic variation commonly observed between ASH1L mutations.

Loss of histone methyltransferase ASH1L in the developing mouse brain causes autistic-like behaviors

Autism spectrum disorder (ASD) is a neurodevelopmental disease associated with various gene mutations. Recent genetic and clinical studies report that mutations of the epigenetic gene ASH1L are highly associated with human ASD and intellectual disability (ID). However, the causality and underlying molecular mechanisms linking ASH1L mutations to genesis of ASD/ID remain undetermined. Here we show loss of ASH1L in the developing mouse brain is sufficient to cause multiple developmental defects, core autistic-like behaviors, and impaired cognitive memory. Gene expression analyses uncover critical roles of ASH1L in regulating gene expression during neural cell development. Thus, our study establishes an ASD/ID mouse model revealing the critical function of an epigenetic factor ASH1L in normal brain development, a causality between Ash1L mutations and ASD/ID-like behaviors in mice, and potential molecular mechanisms linking Ash1L mutations to brain functional abnormalities.

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.

A chromosome 1q22 microdeletion including ASH1L is associated with intellectual disability in a Chinese family

Background

Copy number variants (CNVs) associated with developmental delay and intellectual disability (DD/ID) continue to be identified in patients. This article reports identification of a chromosome 1q22 microdeletion as the genetic cause in a Chinese family affected by ID.

Case presentation

The proband was a 19-year-old pregnant woman referred for genetic counseling and prenatal diagnosis at 18 weeks of gestation. She had severe ID with basically normal stature (height 154 cm [0 SD], weight 61 kg [− 0.2 SD], and head circumference 54 cm [− 1.12 SD]). Her distinctive facial features included a prominent forehead; flat face; flat nasal bridge and a short upturned nose; thin lips; and small ears. The proband’s father was reported to have low intelligence, whereas her mother was of normal intelligence but with scoliosis. Chromosome microarray analysis (CMA) reveals that the proband, her father and the fetus all carry a 1q22 microdeletion of 936.3 Kb (arr[GRCh37] 1q22 (155016052_155952375)×1), which was not observed in her mother and paternal grandparents and uncles, suggesting a de novo mutation in the proband’s father. The microdeletion involves 24 OMIM genes including ASH1L (also known as KMT2H and encoding a histone lysine methyltransferase). Of note, haploinsufficiency of ASH1L has been shown to be associated with neurodevelopmental disorders. Based on the inheritance of the detected CNV in the pedigree and similar CNVs associated with ID in public databases (Decipher, DGV and ClinVar) and literature, the detected CNV is considered as pathogenic. The family chose to terminate the pregnancy.

Conclusions

The identified 1q22 microdeletion including ASH1L is pathogenic and associated with ID. This case broadens the spectrum of ID-related CNVs and may be useful as a reference for clinicians.

Novel role of ASH1L histone methyltransferase in anaplastic thyroid carcinoma

Anaplastic thyroid cancer (ATC) is one of the most aggressive human malignancies, with an average life expectancy of ∼6 months from the time of diagnosis. The genetic and epigenetic changes that underlie this malignancy are incompletely understood. We found that ASH1-like histone lysine methyltransferase (ASH1L) is overexpressed in ATC relative to the much less aggressive and more common differentiated thyroid cancer. This increased expression was due at least in part to reduced levels of microRNA-200b-3p (miR-200b-3p), which represses ASH1L expression, in ATC. Genetic knockout of ASH1L protein expression in ATC cell lines decreased cell growth both in culture and in mouse xenografts. RNA-Seq analysis of ASH1L knockout versus WT ATC cell lines revealed that ASH1L is involved in the regulation of numerous cancer-related genes and gene sets. The pro-oncogenic long noncoding RNA colon cancer-associated transcript 1 (CCAT1) was one of the most highly (approximately 68-fold) down-regulated transcripts in ASH1L knockout cells. Therefore, we investigated CCAT1 as a potential mediator of the growth-inducing activity of ASH1L. Supporting this hypothesis, CCAT1 knockdown in ATC cells decreased their growth rate, and ChIP-Seq data indicated that CCAT1 is likely a direct target of ASH1L's histone methyltransferase activity. These results indicate that ASH1L contributes to the aggressiveness of ATC and suggest that ASH1L, along with its upstream regulator miR-200b-3p and its downstream mediator CCAT1, represents a potential therapeutic target in ATC.

A chromatin scaffold for DNA damage recognition: how histone methyltransferases prime nucleosomes for repair of ultraviolet light-induced lesions

The excision of mutagenic DNA adducts by the nucleotide excision repair (NER) pathway is essential for genome stability, which is key to avoiding genetic diseases, premature aging, cancer and neurologic disorders. Due to the need to process an extraordinarily high damage density embedded in the nucleosome landscape of chromatin, NER activity provides a unique functional caliper to understand how histone modifiers modulate DNA damage responses. At least three distinct lysine methyltransferases (KMTs) targeting histones have been shown to facilitate the detection of ultraviolet (UV) light-induced DNA lesions in the difficult to access DNA wrapped around histones in nucleosomes. By methylating core histones, these KMTs generate docking sites for DNA damage recognition factors before the chromatin structure is ultimately relaxed and the offending lesions are effectively excised. In view of their function in priming nucleosomes for DNA repair, mutations of genes coding for these KMTs are expected to cause the accumulation of DNA damage promoting cancer and other chronic diseases. Research on the question of how KMTs modulate DNA repair might pave the way to the development of pharmacologic agents for novel therapeutic strategies.

Mutations in ASH1L confer susceptibility to Tourette syndrome

Tourette syndrome (TS) is a childhood-onset neuropsychiatric disorder characterized by repetitive motor movements and vocal tics. The clinical manifestations of TS are complex and often overlap with other neuropsychiatric disorders. TS is highly heritable; however, the underlying genetic basis and molecular and neuronal mechanisms of TS remain largely unknown. We performed whole-exome sequencing of a hundred trios (probands and their parents) with detailed records of their clinical presentations and identified a risk gene, ASH1L, that was both de novo mutated and associated with TS based on a transmission disequilibrium test. As a replication, we performed follow-up targeted sequencing of ASH1L in additional 524 unrelated TS samples and replicated the association (P value = 0.001). The point mutations in ASH1L cause defects in its enzymatic activity. Therefore, we established a transgenic mouse line and performed an array of anatomical, behavioral, and functional assays to investigate ASH1L function. The Ash1l^+/- mice manifested tic-like behaviors and compulsive behaviors that could be rescued by the tic-relieving drug haloperidol. We also found that Ash1l disruption leads to hyper-activation and elevated dopamine-releasing events in the dorsal striatum, all of which could explain the neural mechanisms for the behavioral abnormalities in mice. Taken together, our results provide compelling evidence that ASH1L is a TS risk gene.