Neurodevelopmental disorders that arise from de novo mutations in chromatin-remodelling genes lack targeted treatments. Snijders Blok-Campeau syndrome (SNIBCPS)1, which is caused by pathogenic variants in CHD3, manifests with intellectual disability, autistic-like behaviours and motor deficits2. Whether somatic gene correction can reverse such phenotypes in vivo remains unknown. Here we show that modelling the recurrent CHD3 variant p.R1025W in a humanized mouse model (Chd3hR1025W/+) recapitulates key features of SNIBCPS, including reduced CHD3 protein levels and abnormalities in social communication, cognition and motor coordination. We engineered a TadA-embedded adenine base editor (TeABE) and delivered it brain-wide using a dual adeno-associated virus (AAV) system and achieved efficient on-target A•T-to-G•C correction across multiple cortical and hippocampal regions with minimal bystander activity. This intervention restored CHD3 levels and ameliorated behavioural abnormalities in vivo. Furthermore, intrathecal dual AAV delivery in nonhuman primates resulted in widespread neuronal transduction and efficient TeABE reconstitution, a result that supports its translational feasibility. These findings establish in vivo base editing as a viable therapeutic approach for CHD3-related neurodevelopmental disease. More broadly, they demonstrate that precise single-base correction in the postnatal brain can restore protein dosage and function, thereby offering a framework for the treatment of monogenic neurodevelopmental disorders.

Snijders Blok-Campeau syndrome (SNIBCPS), a neurodevelopmental disorder first described in 2018, is caused by heterozygous pathogenic variants in CHD3. Its encoded protein plays a crucial role in the development of the nervous system of embryos. While phenotypic traits have been broadly defined, i.e., global neurodevelopmental delays such as intellectual disabilities and delayed speech acquisition, and physical features such as characteristic facial features and macrocephaly, the phenotypic spectrum has not been further assessed. We present the neurobehavioral profile of 38 individuals with variants in CHD3 and compare it to the ones of autism spectrum disorder (ASD) and Fragile X syndrome (FXS) cohorts. Profound clinical deficits were found in adaptive functioning, communication skills, and sensorimotor functioning in most SNIBCPS participants. Similarities between FXS and SNIBCPS cohorts were unveiled, characterized by diminished levels of global adaptive behavior and adaptive functioning in the social and communication domains. Nevertheless, despite profound challenges in global adaptive behavior in SNIBCPS, we reveal the social domain as showing the highest adaptive levels alongside minimal emotional/behavioral issues within the sample, suggesting relative strengths inherent to SNIBCPS. This study enriches the scarce SNIBCPS literature by delineating the neurobehavioral phenotypic spectrum of SNIBCPS and by innovating comparisons with clinically akin neurodevelopmental disorders.

Chromatin remodeling is an important system controlling gene expression. CHD3, which is a causative gene of Snijders Blok-Campeau syndrome (SNIBCPS), is a member of the chromodomain helicase DNA-binding (CHD) family related to chromatin remodeling. SNIBCPS is characterized by developmental delay (DD), intellectual disability (ID), macrocephaly, and facial features including a prominent forehead and hypertelorism. Hypersociability/overfriendliness is a notable behavioral feature in patients. Here, we describe five SNIBCPS patients with CHD3 variants from four families, including a sibling pair caused by parental gonosomal mosaicism. We observed two distinct phenotypes in our patients in accordance with previous observations. Phenotype 1: macrocephaly, hypertelorism, overgrowth, DD, and ID; and Phenotype 2: microcephaly, growth retardation, DD, and ID. Phenotype 1 was consistent with the typical SNIBCPS phenotype, while Phenotype 2 was distinct. To understand further the features of the patients with SNIBCPS, we generated chd3-knockout (KO) zebrafish using CRISPR-Cas9 genome editing. No morphological changes were observed in chd3-KO zebrafish. However, behavioral tests showed that chd3-KO zebrafish had strong and sustained interest in others, and were less aggressive toward others, suggesting a recapitulation of the hypersociability/overfriendliness phenotype in patients with SNIBCPS. Metabolomic analysis using whole brains showed changes in metabolites processed by specific mitochondrial enzymes in chd3-KO zebrafish. The administration of metformin, which reportedly ameliorates mitochondrial dysfunction and behavioral abnormalities, attenuated the abnormal behavior of chd3-KO zebrafish. Our study helps delineate the phenotypes of patients with SNIBCPS, provides insights into a characteristic behavior of the disease, and suggests a potential treatment to improve the behavioral symptoms of patients.

Snijders Blok-Campeau Syndrome (SNIBCPS) is a neurodevelopmental disorder characterized by intellectual disability, developmental delays, speech impairment, hypotonia, and distinctive facial features. Little is known about pain perception in children with cognitive impairments, such as patients with SNIBCPS. Although it has been noted that some individuals with SNIBCPS have decreased pain sensation and response to painful stimuli, these reports are anecdotal. Therefore, the objective was to better understand this syndrome and the affected individual's perception and response to pain through proxy-reported observational assessments. Fifteen caregivers of individuals with a diagnosis of SNIBCPS participated in this mixed-methods anonymous survey study between July and September 2024. The survey questionnaires included the Pediatric Pain Profile, a Pain Sensory Questionnaire, the Non-Communicative Children's Pain Checklist-Revised, and the Individualized Numerical Rating Scale. Almost a quarter of our respondents reported insensitivity in the affected individual to hard impacts or pressure. Our findings highlight early and past painful experiences in individuals with SNIBCPS who have a range of behaviors to express their pain. Our findings bring awareness about the proper examination of individuals with SNIBCPS. Despite the small sample size, our findings suggest that pain and injuries may go unreported in individuals with SNIBCPS, and individualized parental observational scales may be beneficial for their healthcare providers and their caregivers.

Pathogenic genetic variants in the NuRD component CHD3 cause Snijders Blok-Campeau Syndrome, a neurodevelopmental disorder manifesting with intellectual disability and craniofacial anomalies. To investigate the role of CHD3 in craniofacial development, we differentiated control and CHD3-depleted human-induced pluripotent stem cells into cranial neural crest cells (CNCCs). In control lines, CHD3 is upregulated in early stages of CNCC specification, where it enhances the BMP signalling response by opening chromatin at BMP-responsive cis-regulatory elements and by increasing expression of BMP-responsive transcription factors, including DLX paralogs. CHD3 loss leads to repression of BMP target genes and loss of chromatin accessibility at cis-regulatory elements usually bound by BMP-responsive factors, causing an imbalance between BMP and Wnt signalling. Consequently, the CNCC specification fails, replaced by aberrant early-mesoderm identity, which can be partially rescued by titrating Wnt levels. Our findings highlight a novel role for CHD3 as a pivotal regulator of BMP signalling, essential for proper neural crest specification and craniofacial development. Moreover, these results suggest a molecular mechanism for the craniofacial anomalies of Snijders Blok-Campeau Syndrome.