Partial deletion of TCF4 in three generation family with non-syndromic intellectual disability, without features of Pitt-Hopkins syndrome

Expression of alternative transcription factor 4 mRNAs and protein isoforms in the developing and adult rodent and human tissues

Transcription factor 4 (TCF4) belongs to the class I basic helix-loop-helix family of transcription factors (also known as E-proteins) and is vital for the development of the nervous system. Aberrations in the TCF4 gene are associated with several neurocognitive disorders such as schizophrenia, intellectual disability, post-traumatic stress disorder, depression, and Pitt-Hopkins Syndrome, a rare but severe autism spectrum disorder. Expression of the human TCF4 gene can produce at least 18 N-terminally distinct protein isoforms, which activate transcription with different activities and thus may vary in their function during development. We used long-read RNA-sequencing and western blot analysis combined with the analysis of publicly available short-read RNA-sequencing data to describe both the mRNA and protein expression of the many distinct TCF4 isoforms in rodent and human neural and nonneural tissues. We show that TCF4 mRNA and protein expression is much higher in the rodent brain compared to nonneural tissues. TCF4 protein expression is highest in the rodent cerebral cortex and hippocampus, where expression peaks around birth, and in the rodent cerebellum, where expression peaks about a week after birth. In human, highest TCF4 expression levels were seen in the developing brain, although some nonneural tissues displayed comparable expression levels to adult brain. In addition, we show for the first time that out of the many possible TCF4 isoforms, the main TCF4 isoforms expressed in the rodent and human brain and other tissues are TCF4-B, -C, -D, -A, and-I. Taken together, our isoform specific analysis of TCF4 expression in different tissues could be used for the generation of gene therapy applications for patients with TCF4-associated diseases.

The recurrent TCF4 missense variant p.(Arg389Cys) causes a neurodevelopmental disorder overlapping with but not typical for Pitt-Hopkins syndrome

TCF4 haploinsufficiency by deletions, truncating variants or loss-of-function missense variants within the DNA-binding and protein interacting bHLH domain causes Pitt-Hopkins syndrome (PTHS). This neurodevelopmental disorder (NDD) is characterized by severe intellectual disability (ID), epilepsy, hyperbreathing and a typical facial gestalt. Only few aberrations of the N-terminus of TCF4 were associated with milder or atypical phenotypes. By personal communication and searching databases we assembled six cases with the novel, recurrent, de novo missense variant c.1165C > T, p.(Arg389Cys) in TCF4. This variant was identified by diagnostic exome or panel sequencing and is located upstream of the bHLH domain. All six individuals presented with moderate to severe ID with language impairment. Microcephaly occurred in two individuals, epilepsy only in one, and no breathing anomalies or myopia were reported. Facial gestalt showed some aspects of PTHS but was rather non-specific in most individuals. Interestingly, the variant is located within the AD2 activation domain next to a highly conserved coactivator-recruitment motif and might alter interaction with coactivator proteins independently from the bHLH domain. Our findings of a recurrent missense variant outside the bHLH domain in six individuals with an ID phenotype overlapping with but not typical for PTHS delineate a novel genotype-phenotype correlation for TCF4-related NDDs. This article is protected by copyright. All rights reserved.

Incomplete Penetrance and Variable Expressivity: From Clinical Studies to Population Cohorts

The same genetic variant found in different individuals can cause a range of diverse phenotypes, from no discernible clinical phenotype to severe disease, even among related individuals. Such variants can be said to display incomplete penetrance, a binary phenomenon where the genotype either causes the expected clinical phenotype or it does not, or they can be said to display variable expressivity, in which the same genotype can cause a wide range of clinical symptoms across a spectrum. Both incomplete penetrance and variable expressivity are thought to be caused by a range of factors, including common variants, variants in regulatory regions, epigenetics, environmental factors, and lifestyle. Many thousands of genetic variants have been identified as the cause of monogenic disorders, mostly determined through small clinical studies, and thus, the penetrance and expressivity of these variants may be overestimated when compared to their effect on the general population. With the wealth of population cohort data currently available, the penetrance and expressivity of such genetic variants can be investigated across a much wider contingent, potentially helping to reclassify variants that were previously thought to be completely penetrant. Research into the penetrance and expressivity of such genetic variants is important for clinical classification, both for determining causative mechanisms of disease in the affected population and for providing accurate risk information through genetic counseling. A genotype-based definition of the causes of rare diseases incorporating information from population cohorts and clinical studies is critical for our understanding of incomplete penetrance and variable expressivity. This review examines our current knowledge of the penetrance and expressivity of genetic variants in rare disease and across populations, as well as looking into the potential causes of the variation seen, including genetic modifiers, mosaicism, and polygenic factors, among others. We also considered the challenges that come with investigating penetrance and expressivity.

Functional consequences of TCF4 missense substitutions associated with Pitt-Hopkins syndrome, mild intellectual disability, and schizophrenia

Transcription factor 4 (TCF4) is a basic helix-loop-helix transcription factor essential for neurocognitive development. The aberrations in TCF4 are associated with neurodevelopmental disorders including schizophrenia, intellectual disability, and Pitt-Hopkins syndrome, an autism-spectrum disorder characterized by developmental delay. Several disease-associated missense mutations in TCF4 have been shown to interfere with TCF4 function, but for many mutations, the impact remains undefined. Here, we tested the effects of 12 functionally uncharacterized disease-associated missense mutations and variations in TCF4 using transient expression in mammalian cells, confocal imaging, in vitro DNA-binding assays, and reporter assays. We show that Pitt-Hopkins syndrome-associated missense mutations within the basic helix-loop-helix domain of TCF4 and a Rett-like syndrome-associated mutation in a transcription activation domain result in altered DNA-binding and transcriptional activity of the protein. Some of the missense variations found in schizophrenia patients slightly increase TCF4 transcriptional activity, whereas no effects were detected for missense mutations linked to mild intellectual disability. We in addition find that the outcomes of several disease-related mutations are affected by cell type, TCF4 isoform, and dimerization partner, suggesting that the effects of TCF4 mutations are context-dependent. Together with previous work, this study provides a basis for the interpretation of the functional consequences of TCF4 missense variants.

Molecular and Cellular Function of Transcription Factor 4 in Pitt-Hopkins Syndrome

Transcription factor 4 (TCF4, also known as ITF2 or E2-2) is a type I basic helix-loop-helix transcription factor. Autosomal dominant mutations in TCF4 cause Pitt-Hopkins syndrome (PTHS), a rare syndromic form of autism spectrum disorder. In this review, we provide an update on the progress regarding our understanding of TCF4 function at the molecular, cellular, physiological, and behavioral levels with a focus on phenotypes and therapeutic interventions. We examine upstream and downstream regulatory networks associated with TCF4 and discuss a range of in vitro and in vivo data with the aim of understanding emerging TCF4-specific mechanisms relevant for disease pathophysiology. In conclusion, we provide comments about exciting future avenues of research that may provide insights into potential new therapeutic targets for PTHS.

Transcription factor 4 and its association with psychiatric disorders

The human transcription factor 4 gene (TCF4) encodes a helix-loop-helix transcription factor widely expressed throughout the body and during neural development. Mutations in TCF4 cause a devastating autism spectrum disorder known as Pitt-Hopkins syndrome, characterized by a range of aberrant phenotypes including severe intellectual disability, absence of speech, delayed cognitive and motor development, and dysmorphic features. Moreover, polymorphisms in TCF4 have been associated with schizophrenia and other psychiatric and neurological conditions. Details about how TCF4 genetic variants are linked to these diseases and the role of TCF4 during neural development are only now beginning to emerge. Here, we provide a comprehensive review of the functions of TCF4 and its protein products at both the cellular and organismic levels, as well as a description of pathophysiological mechanisms associated with this gene.

Enriched environment ameliorates adult hippocampal neurogenesis deficits in Tcf4 haploinsufficient mice

Background

Transcription factor 4 (TCF4) has been linked to human neurodevelopmental disorders such as intellectual disability, Pitt-Hopkins Syndrome (PTHS), autism, and schizophrenia. Recent work demonstrated that TCF4 participates in the control of a wide range of neurodevelopmental processes in mammalian nervous system development including neural precursor proliferation, timing of differentiation, migration, dendritogenesis and synapse formation. TCF4 is highly expressed in the adult hippocampal dentate gyrus – one of the few brain regions where neural stem / progenitor cells generate new functional neurons throughout life.

Results

We here investigated whether TCF4 haploinsufficiency, which in humans causes non-syndromic forms of intellectual disability and PTHS, affects adult hippocampal neurogenesis, a process that is essential for hippocampal plasticity in rodents and potentially in humans. Young adult Tcf4 heterozygote knockout mice showed a major reduction in the level of adult hippocampal neurogenesis, which was at least in part caused by lower stem/progenitor cell numbers and impaired maturation and survival of adult-generated neurons. Interestingly, housing in an enriched environment was sufficient to enhance maturation and survival of new neurons and to substantially augment neurogenesis levels in Tcf4 heterozygote knockout mice.

Conclusion

The present findings indicate that haploinsufficiency for the intellectual disability- and PTHS-linked transcription factor TCF4 not only affects embryonic neurodevelopment but impedes neurogenesis in the hippocampus of adult mice. These findings suggest that TCF4 haploinsufficiency may have a negative impact on hippocampal function throughout adulthood by impeding hippocampal neurogenesis.

The Fuchs corneal dystrophy-associated CTG repeat expansion in the TCF4 gene affects transcription from its alternative promoters

The CTG trinucleotide repeat (TNR) expansion in Transcription factor 4 (TCF4) intron 3 is the main cause of Fuchs’ endothelial corneal dystrophy (FECD) and may confer an increased risk of developing bipolar disorder (BD). Usage of alternative 5′ exons for transcribing the human TCF4 gene results in numerous TCF4 transcripts which encode for at least 18 N-terminally different protein isoforms that vary in their function and transactivation capability. Here we studied the TCF4 region containing the CTG TNR and characterized the transcription initiation sites of the nearby downstream 5′ exons 4a, 4b and 4c. We demonstrate that these exons are linked to alternative promoters and show that the CTG TNR expansion decreases the activity of the nearby downstream TCF4 promoters in primary cultured neurons. We confirm this finding using two RNA sequencing (RNA-seq) datasets of corneal endothelium from FECD patients with expanded CTG TNR in the TCF4 gene. Furthermore, we report an increase in the expression of various other TCF4 transcripts in FECD, possibly indicating a compensatory mechanism. We conclude that the CTG TNR affects TCF4 expression in a transcript-specific manner both in neurons and in the cornea.

Modulation of cognition and neuronal plasticity in gain- and loss-of-function mouse models of the schizophrenia risk gene Tcf4

The transcription factor TCF4 was confirmed in several large genome-wide association studies as one of the most significant schizophrenia (SZ) susceptibility genes. Transgenic mice moderately overexpressing Tcf4 in forebrain (Tcf4tg) display deficits in fear memory and sensorimotor gating. As second hit, we exposed Tcf4tg animals to isolation rearing (IR), chronic social defeat (SD), enriched environment (EE), or handling control (HC) conditions and examined mice with heterozygous deletion of the exon 4 (Tcf4Ex4δ^+/-) to unravel gene-dosage effects. We applied multivariate statistics for behavioral profiling and demonstrate that IR and SD cause strong cognitive deficits of Tcf4tg mice, whereas EE masked the genetic vulnerability. We observed enhanced long-term depression in Tcf4tg mice and enhanced long-term potentiation in Tcf4Ex4δ^+/- mice indicating specific gene-dosage effects. Tcf4tg mice showed higher density of immature spines during development as assessed by STED nanoscopy and proteomic analyses of synaptosomes revealed concurrently increased levels of proteins involved in synaptic function and metabolic pathways. We conclude that environmental stress and Tcf4 misexpression precipitate cognitive deficits in 2-hit mouse models of relevance for schizophrenia.

Region and Cell Type Distribution of TCF4 in the Postnatal Mouse Brain

Transcription factor 4 is a class I basic helix-loop-helix transcription factor regulating gene expression. Altered TCF4 gene expression has been linked to non-syndromic intellectual disability, schizophrenia, and a severe neurodevelopmental disorder known as Pitt-Hopkins syndrome. An understanding of the cell types expressing TCF4 protein in the mouse brain is needed to help identify potential pathophysiological mechanisms and targets for therapeutic delivery in TCF4-linked disorders. Here we developed a novel green fluorescent protein reporter mouse to visualize TCF4-expressing cells throughout the brain. Using this TCF4 reporter mouse, we observed prominent expression of TCF4 in the pallial region and cerebellum of the postnatal brain. At the cellular level, both glutamatergic and GABAergic neurons express TCF4 in the cortex and hippocampus, while only a subset of GABAergic interneurons express TCF4 in the striatum. Among glial cell groups, TCF4 is present in astrocytes and immature and mature oligodendrocytes. In the cerebellum, cells in the granule and molecular layer express TCF4. Our findings greatly extend our knowledge of the spatiotemporal and cell type-specific expression patterns of TCF4 in the brain, and hence, lay the groundwork to better understand TCF4-linked neurological disorders. Any effort to restore TCF4 functions through small molecule or genetic therapies should target these brain regions and cell groups to best recapitulate TCF4 expression patterns.

Deconvolution of transcriptional networks identifies TCF4 as a master regulator in schizophrenia

Applying tissue-specific deconvolution of transcriptional networks to identify their master regulators (MRs) in neuropsychiatric disorders has been largely unexplored. Here, using two schizophrenia (SCZ) case-control RNA-seq datasets, one on postmortem dorsolateral prefrontal cortex (DLPFC) and another on cultured olfactory neuroepithelium, we deconvolved the transcriptional networks and identified TCF4 as a top candidate MR that may be dysregulated in SCZ. We validated TCF4 as a MR through enrichment analysis of TCF4-binding sites in induced pluripotent stem cell (hiPSC)-derived neurons and in neuroblastoma cells. We further validated the predicted TCF4 targets by knocking down TCF4 in hiPSC-derived neural progenitor cells (NPCs) and glutamatergic neurons (Glut_Ns). The perturbed TCF4 gene network in NPCs was more enriched for pathways involved in neuronal activity and SCZ-associated risk genes, compared to Glut_Ns. Our results suggest that TCF4 may serve as a MR of a gene network dysregulated in SCZ at early stages of neurodevelopment.

Diagnosis and management in Pitt-Hopkins syndrome: First international consensus statement

Pitt-Hopkins syndrome (PTHS) is a neurodevelopmental disorder characterized by intellectual disability, specific facial features, and marked autonomic nervous system dysfunction, especially with disturbances of regulating respiration and intestinal mobility. It is caused by variants in the transcription factor TCF4. Heterogeneity in the clinical and molecular diagnostic criteria and care practices has prompted a group of international experts to establish guidelines for diagnostics and care. For issues, for which there was limited information available in international literature, we collaborated with national support groups and the participants of a syndrome specific international conference to obtain further information. Here, we discuss the resultant consensus, including the clinical definition of PTHS and a molecular diagnostic pathway. Recommendations for managing particular health problems such as dysregulated respiration are provided. We emphasize the need for integration of care for physical and behavioral issues. The recommendations as presented here will need to be evaluated for improvements to allow for continued optimization of diagnostics and care.

Prioritization of Variants Detected by Next Generation Sequencing According to the Mutation Tolerance and Mutational Architecture of the Corresponding Genes

The biggest challenge geneticists face when applying next-generation sequencing technology to the diagnosis of rare diseases is determining which rare variants, from the dozens or hundreds detected, are potentially implicated in the patient’s phenotype. Thus, variant prioritization is an essential step in the process of rare disease diagnosis. In addition to conducting the usual in-silico analyses to predict variant pathogenicity (based on nucleotide/amino-acid conservation and the differences between the physicochemical features of the amino-acid change), three important concepts should be borne in mind. The first is the “mutation tolerance” of the genes in which variants are located. This describes the susceptibility of a given gene to any functional mutation and depends on the strength of purifying selection acting against it. The second is the “mutational architecture” of each gene. This describes the type and location of mutations previously identified in the gene, and their association with different phenotypes or degrees of severity. The third is the mode of inheritance (inherited vs. de novo) of the variants detected. Here, we discuss the importance of each of these concepts for variant prioritization in the diagnosis of rare diseases. Using real data, we show how genes, rather than variants, can be prioritized by calculating a gene-specific mutation tolerance score. We also illustrate the influence of mutational architecture on variant prioritization using five paradigmatic examples. Finally, we discuss the importance of familial variant analysis as final step in variant prioritization.

Disease-causing variants in TCF4 are a frequent cause of intellectual disability: lessons from large-scale sequencing approaches in diagnosis

High-throughput sequencing (HTS) of human genome coding regions allows the simultaneous screen of a large number of genes, significantly improving the diagnosis of non-syndromic intellectual disabilities (ID). HTS studies permit the redefinition of the phenotypical spectrum of known disease-causing genes, escaping the clinical inclusion bias of gene-by-gene Sanger sequencing. We studied a cohort of 903 patients with ID not reminiscent of a well-known syndrome, using an ID-targeted HTS of several hundred genes and found de novo heterozygous variants in TCF4 (transcription factor 4) in eight novel patients. Piecing together the patients from this study and those from previous large-scale unbiased HTS studies, we estimated the rate of individuals with ID carrying a disease-causing TCF4 mutation to 0.7%. So far, TCF4 molecular abnormalities were known to cause a syndromic form of ID, Pitt-Hopkins syndrome (PTHS), which combines severe ID, developmental delay, absence of speech, behavioral and ventilation disorders, and a distinctive facial gestalt. Therefore, we reevaluated ten patients carrying a pathogenic or likely pathogenic variant in TCF4 (eight patients included in this study and two from our previous ID-HTS study) for PTHS criteria defined by Whalen and Marangi. A posteriori, five patients had a score highly evocative of PTHS, three were possibly consistent with this diagnosis, and two had a score below the defined PTHS threshold. In conclusion, these results highlight TCF4 as a frequent cause of moderate to profound ID and broaden the clinical spectrum associated to TCF4 mutations to nonspecific ID.

Pitt-Hopkins Syndrome: A Review of Current Literature, Clinical Approach, and 23-Patient Case Series

Pitt-Hopkins syndrome (PTHS) is a rare, genetic disorder caused by a molecular variant of TCF4 which is involved in embryologic neuronal differentiation. PTHS is characterized by syndromic facies, psychomotor delay, and intellectual disability. Other associated features include early-onset myopia, seizures, constipation, and hyperventilation-apneic spells. Many also meet criteria for autism spectrum disorder. Here the authors present a series of 23 PTHS patients with molecularly confirmed TCF4 variants and describe 3 unique individuals. The first carries a small deletion but does not exhibit the typical facial features nor the typical pattern of developmental delay. The second exhibits typical facial features, but has attained more advanced motor and verbal skills than other reported cases to date. The third displays typical features of PTHS, however inherited a large chromosomal duplication involving TCF4 from his unaffected father with somatic mosaicism. To the authors' knowledge, this is the first chromosomal duplication case reported to date.

The Intellectual Disability and Schizophrenia Associated Transcription Factor TCF4 Is Regulated by Neuronal Activity and Protein Kinase A

Transcription factor 4 (TCF4 also known as ITF2 or E2-2) is a basic helix-loop-helix (bHLH) protein associated with Pitt-Hopkins syndrome, intellectual disability, and schizophrenia (SCZ). Here, we show that TCF4-dependent transcription in cortical neurons cultured from embryonic rats of both sexes is induced by neuronal activity via soluble adenylyl cyclase and protein kinase A (PKA) signaling. PKA phosphorylates TCF4 directly and a PKA phosphorylation site in TCF4 is necessary for its transcriptional activity in cultured neurons and in the developing brain in vivo We also demonstrate that Gadd45g (growth arrest and DNA damage inducible gamma) is a direct target of neuronal-activity-induced, TCF4-dependent transcriptional regulation and that TCF4 missense variations identified in SCZ patients alter the transcriptional activity of TCF4 in neurons. This study identifies a new role for TCF4 as a neuronal-activity-regulated transcription factor, offering a novel perspective on the association of TCF4 with cognitive disorders.SIGNIFICANCE STATEMENT The importance of the basic helix-loop-helix transcription factor transcription factor 4 (TCF4) in the nervous system is underlined by its association with common and rare cognitive disorders. In the current study, we show that TCF4-controlled transcription in primary cortical neurons is induced by neuronal activity and protein kinase A. Our results support the hypotheses that dysregulation of neuronal-activity-dependent signaling plays a significant part in the etiology of neuropsychiatric and neurodevelopmental disorders.

Impairment of different protein domains causes variable clinical presentation within Pitt-Hopkins syndrome and suggests intragenic molecular syndromology of TCF4

Pitt-Hopkins syndrome is a neurodevelopmental disorder characterized by severe intellectual disability and a distinctive facial gestalt. It is caused by haploinsufficiency of the TCF4 gene. The TCF4 protein has different functional domains, with the NLS (nuclear localization signal) domain coded by exons 7-8 and the bHLH (basic Helix-Loop-Helix) domain coded by exon 18. Several alternatively spliced TCF4 variants have been described, allowing for translation of variable protein isoforms. Typical PTHS patients have impairment of at least the bHLH domain. To which extent impairment of the remaining domains contributes to the final phenotype is not clear. There is recent evidence that certain loss-of-function variants disrupting TCF4 are associated with mild ID, but not with typical PTHS. We describe a frameshift-causing partial gene deletion encompassing exons 4-6 of TCF4 in an adult patient with mild ID and nonspecific facial dysmorphisms but without the typical features of PTHS, and a c.520C > T nonsense variant within exon 8 in a child presenting with a severe phenotype largely mimicking PTHS, but lacking the typical facial dysmorphism. Investigation on mRNA, along with literature review, led us to suggest a preliminary phenotypic map of loss-of-function variants affecting TCF4. An intragenic phenotypic map of loss-of-function variants in TCF4 is suggested here for the first time: variants within exons 1-4 and exons 4-6 give rise to a recurrent phenotype with mild ID not in the spectrum of Pitt-Hopkins syndrome (biallelic preservation of both the NLS and bHLH domains); variants within exons 7-8 cause a severe phenotype resembling PTHS but in absence of the typical facial dysmorphism (impairment limited to the NLS domain); variants within exons 9-19 cause typical Pitt-Hopkins syndrome (impairment of at least the bHLH domain). Understanding the TCF4 molecular syndromology can allow for proper nosology in the current era of whole genomic investigations.

Distinct selective forces and Neanderthal introgression shaped genetic diversity at genes involved in neurodevelopmental disorders

In addition to high intelligence, humans evolved specialized social-cognitive skills, which are specifically affected in children with autism spectrum disorder (ASD). Genes affected in ASD represent suitable candidates to study the evolution of human social cognition. We performed an evolutionary analysis on 68 genes associated to neurodevelopmental disorders; our data indicate that genetic diversity was shaped by distinct selective forces, including natural selection and introgression from archaic hominins. We discuss the possibility that segregation distortion during spermatogenesis accounts for a subset of ASD mutations. Finally, we detected modern-human-specific alleles in DYRK1A and TCF4. These variants are located within regions that display chromatin features typical of transcriptional enhancers in several brain areas, strongly suggesting a regulatory role. These SNPs thus represent candidates for association with neurodevelopmental disorders, and await experimental validation in future studies.

WNT/β-Catenin Pathway and Epigenetic Mechanisms Regulate the Pitt-Hopkins Syndrome and Schizophrenia Risk Gene

Genetic variation within the transcription factor TCF4 locus can cause the intellectual disability and developmental disorder Pitt-Hopkins syndrome (PTHS), whereas single-nucleotide polymorphisms within noncoding regions are associated with schizophrenia. These genetic findings position TCF4 as a link between transcription and cognition; however, the neurobiology of TCF4 remains poorly understood. Here, we quantitated multiple distinct TCF4 transcript levels in human induced pluripotent stem cell-derived neural progenitors and differentiated neurons, and PTHS patient fibroblasts. We identify two classes of pharmacological treatments that regulate TCF4 expression: WNT pathway activation and inhibition of class I histone deacetylases. In PTHS fibroblasts, both of these perturbations upregulate a subset of TCF4 transcripts. Finally, using chromatin immunoprecipitation sequencing in conjunction with genome-wide transcriptome analysis, we identified TCF4 target genes that may mediate the effect of TCF4 loss on neuroplasticity. Our studies identify new pharmacological assays, tools, and targets for the development of therapeutics for cognitive disorders.

Molecular Mechanisms of Transcription Factor 4 in Pitt Hopkins Syndrome

Purpose of Review

Pitt Hopkins syndrome (PTHS) is a rare neurodevelopmental disorder that results from mutations of the clinically pleiotropic Transcription Factor 4 (TCF4) gene. Mutations in the genomic locus of TCF4 on chromosome 18 have been linked to multiple disorders including 18q syndrome, schizophrenia, Fuch's corneal dystrophy, and sclerosing cholangitis. For PTHS, TCF4 mutation or deletion leads to the production of a dominant negative TCF4 protein and/or haploinsufficiency that results in abnormal brain development. The biology of TCF4 has been studied for several years in regards to its role in immune cell differentiation, although its role in neurodevelopment and the mechanisms resulting in the severe symptoms of PTHS are not well studied.

Recent Findings

Here, we summarize the current understanding of PTHS and recent findings that have begun to describe the biological implications of TCF4 deficiency during brain development and into adulthood. In particular, we focus on recent work that has looked at the role of TCF4 biology within the context of PTHS and highlight the potential for identification of therapeutic targets for PTHS.

Summary

PTHS research continues to uncover mutations in TCF4 that underlie the genetic cause of this rare disease, and emerging evidence for molecular mechanisms that TCF4 regulates in brain development and neuronal function is contributing to a more complete picture of how pathology arises from this genetic basis, with important implications for the potential of future clinical care.