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

A patient with Pitt-Hopkins syndrome with concomitant common variable immunodeficiency

In patients with 18q deletion syndrome (18q-), immunodeficiency, autoimmunity, and allergies have been described in a subset. Pitt-Hopkins syndrome represents a specific subset of patients with 18q- who have a proximal deletion involving the TCF4 gene or a TCF4 variant. Immunodeficiency has been reported in the overall 18q- population; however, immunodeficiency with Pitt-Hopkins syndrome has not been highlighted. This case report details the immunologic evaluations and the associated infections seen in a young adult with Pitt-Hopkins syndrome to underscore the challenges of managing adults with a complex phenotype who develop frequent infections. This patient with Pitt-Hopkins syndrome ultimately fulfilled the diagnostic criteria for common variable immunodeficiency. Immunoglobulin replacement has led to a somewhat improved infection pattern, although she continues to have aspiration events leading to pneumonia. This case highlights the clinical evolution of Pitt-Hopkins syndrome and serves as a reminder that immunodeficiency can occur in this syndrome.

Clinical and genetic characterization of 47 Chinese pediatric patients with Pitt-Hopkins syndrome: a retrospective study

BACKGROUND

Pitt-Hopkins syndrome (PTHS) is a neurodevelopmental disorder that remains underdiagnosed and its clinical presentations and mutation profiles in a diverse population are yet to be evaluated. This retrospective study aims to investigate the clinical and genetic characteristics of Chinese patients with PTHS.

METHODS

The clinical, biochemical, genetic, therapeutic, and follow-up data of 47 pediatric patients diagnosed with PTHS between 2018 and 2021 were retrospectively analyzed.

RESULTS

The Chinese PTHS patients presented with specific facial features and exhibited global developmental delay of wide severity range. The locus heterogeneity of the TCF4 gene in the patients was highlighted, emphasizing the significance of genetic studies for accurate diagnosis, albeit no significant correlations between genotype and phenotype were observed in this cohort. The study also reports the outcomes of patients who underwent therapeutic interventions, such as ketogenic diets and biomedical interventions.

CONCLUSIONS

The findings of this retrospective analysis expand the phenotypic and molecular spectra of PTHS patients. The study underscores the need for a long-term prospective follow-up study to assess potential therapeutic interventions.

Hirschsprung disease

Hirschsprung disease (HSCR) is a rare congenital intestinal disease that occurs in 1 in 5,000 live births. HSCR is characterized by the absence of ganglion cells in the myenteric and submucosal plexuses of the intestine. Most patients present during the neonatal period with the first meconium passage delayed beyond 24 h, abdominal distension and vomiting. Syndromes associated with HSCR include trisomy 21, Mowat-Wilson syndrome, congenital central hypoventilation syndrome, Shah-Waardenburg syndrome and cartilage-hair hypoplasia. Multiple putative genes are involved in familial and isolated HSCR, of which the most common are the RET proto-oncogene and EDNRB. Diagnosis consists of visualization of a transition zone on contrast enema and confirmation via rectal biopsy. HSCR is typically managed by surgical removal of the aganglionic bowel and reconstruction of the intestinal tract by connecting the normally innervated bowel down to the anus while preserving normal sphincter function. Several procedures, namely Swenson, Soave and Duhamel procedures, can be undertaken and may include a laparoscopically assisted approach. Short-term and long-term comorbidities include persistent obstructive symptoms, enterocolitis and soiling. Continued research and innovation to better understand disease mechanisms holds promise for developing novel techniques for diagnosis and therapy, and improving outcomes in patients.

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.

Rescue of behavioral and electrophysiological phenotypes in a Pitt-Hopkins syndrome mouse model by genetic restoration of Tcf4 expression

Pitt-Hopkins syndrome (PTHS) is a neurodevelopmental disorder caused by monoallelic mutation or deletion in the transcription factor 4 (TCF4) gene. Individuals with PTHS typically present in the first year of life with developmental delay and exhibit intellectual disability, lack of speech, and motor incoordination. There are no effective treatments available for PTHS, but the root cause of the disorder, TCF4 haploinsufficiency, suggests that it could be treated by normalizing TCF4 gene expression. Here, we performed proof-of-concept viral gene therapy experiments using a conditional Tcf4 mouse model of PTHS and found that postnatally reinstating Tcf4 expression in neurons improved anxiety-like behavior, activity levels, innate behaviors, and memory. Postnatal reinstatement also partially corrected EEG abnormalities, which we characterized here for the first time, and the expression of key TCF4-regulated genes. Our results support a genetic normalization approach as a treatment strategy for PTHS, and possibly other TCF4-linked disorders.

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.

Pitt-Hopkins syndrome: phenotypic and genotypic description of four unrelated patients and structural analysis of corresponding missense mutations

Pitt-Hopkins syndrome is an underdiagnosed neurodevelopmental disorder which is characterized by specific facial features, early-onset developmental delay, and moderate to severe intellectual disability. The genetic cause, a deficiency of the TCF4 gene, has been established; however, the underlying pathological mechanisms of this disease are still unclear. Herein, we report four unrelated children with different de novo mutations (T606A, K607E, R578C, and V617I) located at highly conserved sites and with clinical phenotypes which present variable degrees of developmental delay and intellectual disability. Three of these four missense mutations have not yet been reported. The patient with V617I mutation exhibits mild intellectual disability and has attained more advanced motor and verbal skills, which is significantly different from other cases reported to date. Molecular dynamics simulations are used to explore the atomic level mechanism of how missense mutations impair the functions of TCF4. Mutations T606A, K607E, and R578C are found to affect DNA binding directly or indirectly, while V617I only induces subtle conformational changes, which is consistent with the milder clinical phenotype of the corresponding patient. The study expands the mutation spectrum and phenotypic characteristics of Pitt-Hopkins syndrome, and reinforces the genotype-phenotype correlation and strengthens the understanding of phenotype variability, which is helpful for further investigation of pathogenetic mechanisms and improved genetic counseling.

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.

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.

Pitt-Hopkins Syndrome: Clinical and Molecular Findings of a 5-Year-Old Patient

Pitt Hopkins syndrome (PTHS) is a very rare condition and until now, approximately 500 patients were reported worldwide, of which not all are genetically confirmed. Usually, individuals with variants affecting exons 1 to 5 in the TCF4 gene associate mild intellectual disability (ID), between exons 5 to 8, moderate to severe ID and sometimes have some of the characteristics of PTHS, and variants starting from exon 9 to exon 20 associate a typical PTHS phenotype. In this report, we describe the clinical and molecular findings of a Caucasian boy diagnosed with PTHS. PTHS phenotype is described including craniofacial dysmorphism with brachycephaly, biparietal narrowing, wide nasal bridge, thin and linear lateral eyebrows, palpebral edema, full cheeks, short philtrum, wide mouth with prominent and everted lips, prominent Cupid’s bow, downturned corners of the mouth, microdontia and also the clinical management of the patient. The previously and the current diagnosis scores are described in this report and also the challenges and their benefits for an accurate and early diagnosis.

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.