Case Report: A de novo CTNNB1 Nonsense Mutation Associated With Neurodevelopmental Disorder, Retinal Detachment, Polydactyly

Congenital heart defects in CTNNB1 syndrome: Raising clinical awareness

CTNNB1 [OMIM *116806] encodes β-catenin, an integral part of the cadherin/catenin complex, which functions as effector of Wnt signaling. CTNNB1 is highly expressed in brain as well as in other tissues, including heart. Heterozygous CTNNB1 pathogenic variations are associated with a neurodevelopmental disorder characterized by spastic diplegia and visual defects (NEDSDV) [OMIM #615075], featuring psychomotor delay, intellectual disability, behavioral disturbances, movement disorders, visual defects and subtle facial and somatic features. We report on a new series of 19 NEDSDV patients (mean age 10.3 years), nine of whom bearing novel CTNNB1 variants. Notably, five patients showed congenital heart anomalies including absent pulmonary valve with intact ventricular septum, atrioventricular canal with hypoplastic aortic arch, tetralogy of Fallot, and mitral valve prolapse. We focused on the cardiac phenotype characterizing such cases and reviewed the congenital heart defects in previously reported NEDSDV patients. While congenital heart defects had occasionally been reported so far, the present findings configure a higher rate of cardiac anomalies, suggesting dedicated heart examination to NEDSDV clinical management.

CTNNB1-related neurodevelopmental disorder mimics cerebral palsy: case report

While somatic gain-of-function mutations in the CTNNB1 gene cause diverse malignancies, germline loss-of-function mutations cause neurodevelopmental disorders or familial exudative vitreoretinopathy. In particular, CTNNB1-related neurodevelopmental disorders have various phenotypes, and a genotype-phenotype relationship has not been established. We report two patients with CTNNB1-related neurodevelopmental disorder whose clinical features were similar to those of cerebral palsy, hindering diagnosis.

CTNNB1 in neurodevelopmental disorders

CTNNB1 is the gene that encodes β-catenin which acts as a key player in the Wnt signaling pathway and regulates cellular homeostasis. Most CTNNB1-related studies have been mainly focused on its role in cancer. Recently, CTNNB1 has also been found involved in neurodevelopmental disorders (NDDs), such as intellectual disability, autism, and schizophrenia. Mutations of CTNNB1 lead to the dysfunction of the Wnt signaling pathway that regulates gene transcription and further disturbs synaptic plasticity, neuronal apoptosis, and neurogenesis. In this review, we discuss a wide range of aspects of CTNNB1 and its physiological and pathological functions in the brain. We also provide an overview of the most recent research regarding CTNNB1 expression and its function in NDDs. We propose that CTNNB1 would be one of the top high-risk genes for NDDs. It could also be a potential therapeutic target for the treatment of NDDs.

Whole Exome Sequencing Identified two Novel Truncation Mutations in the CTNNB1 Gene Associated with Neurodevelopmental Disorder, Language Dysfunction, and Microcephaly in Chinese Children

Recently, the loss-of-function, heterozygous, and de novo mutations of the CTNNB1 gene have been proven to be partially responsible for intellectual disability in some patients. Herein, we report two unrelated children with neurodevelopmental disorder, abnormal facial features, speech impairments, microcephaly, and dystonia. Based on whole exome sequencing (WES), two new heterozygous and pathogenic mutations in exon 10 (c.1586dupA:p.Q530Afs*42) and exon 4 (c.257dup:p.Y86*) were identified in the CTNNB1 gene for the first time. These findings not only enrich the genetic spectrum of the CTNNB1 gene but also provide evidence for its role in neuronal development.

Genetic and clinical characteristics of 24 mainland Chinese patients with CTNNB1 loss-of-function variants

BACKGROUND

Neurodevelopmental disorder with spastic diplegia and visual defects (NEDSDV) is a rare autosomal dominant syndrome, which is caused by the heterozygous germline loss-of-function variants in CTNNB1.

METHODS

We evaluated the clinical and genetic findings of 24 previously undescribed Chinese patients affected by CTNNB1-related disorders and explored the possible ethnicity-related phenotypic variations.

RESULTS

Twenty-one loss-of-function variants were identified within these 24 NEDSDV patients, including 14 novel CTNNB1 variants and 7 recurrent ones. The prominent clinical manifestations in our cohort are developmental delay/intellectual disability (100%), motor delay (100%), speech impairment (100%), dystonia (87.5%) and microcephaly (69.6%). The common facial dysmorphisms were consistent with previous reports, including wide nasal bridge (58.3%), bulbous nose (45.8%), long philtrum (45.8%) and thin upper lip (45.8%). In addition, 19 patients (79.2%) in our cohort had mild visual defects, while one affected individual (4.2%) had familial exudative vitreoretinopathy. Notably, we discovered that 20 patients (83.3%) exhibited various behavioral abnormalities, which is described in Chinese patients for the first time.

CONCLUSION

We provided the largest known Chinese cohort with pathogenic CTNNB1 variants, which not only helps to expand the variant spectrum of CTNNB1 gene, but further delineates the typical phenotype of this disorder in Chinese population.

Genome-wide DNA methylation profiling and exome sequencing resolved a long-time misdiagnosed case

The search for aetiology of Mendelian disorders is traditionally based on the observation of clinical phenotypes and molecular screening of associated genes. However, a disease-specific diagnosis can be challenging. In this study we detail how the combinatorial genomic and epigenomic assessment allowed to find the underlying molecular event of a clinical case that remained misdiagnosed for years. The individual was referred as affected by an atypical form of Kabuki syndrome with a variant of uncertain significance in the KMT2D gene. However, significant inconsistencies with this diagnosis emerged upon familial segregation of the variant and after the clinical re-evaluation. Therefore, we applied an epigenomic strategy by studying the DNA methylation profile which resulted not consistent with the Kabuki syndrome episignature or with any other disorder-specific episignature described so far, providing strong evidence that the Kabuki syndrome diagnosis does not apply. This result led us to further investigate for epigenetic machinery diseases by using a multigene panel for chromatinopathies. Since this analysis yielded negative results, we applied a whole exome sequencing and identified a de novo pathogenic variant in the CTNNB1 gene associated to NEDSDV syndrome, a neurodevelopmental disorder characterized by intellectual disability and craniofacial anomalies. Based on molecular results and the updated clinical features, we confirmed the NEDSDV diagnosis. Our findings show that the combination of genomic and epigenomics strategies, along with a deeper analysis of clinical phenotype, may provide a significant improvement in the diagnostic protocols for rare genetic disorders and help resolve long-time misdiagnosed and unsolved case.

The extended clinical and genetic spectrum of CTNNB1-related neurodevelopmental disorder

PURPOSE

Loss-of-function mutations of CTNNB1 have been established as the cause of neurodevelopmental disorder with spastic diplegia and visual defects. Although most patients share key phenotypes such as global developmental delay and intellectual disability, patients with CTNNB1-related neurodevelopmental disorder show a broad spectrum of clinical features.

METHODS

We enrolled 13 Korean patients with CTNNB1-related neurodevelopmental disorder who visited Seoul National University Children's Hospital (5 female and 8 male patients with ages ranging from 4 to 22 years). They were all genetically confirmed as having pathogenic loss-of-function variants in CTNNB1 using trio or singleton whole exome sequencing. Variants called from singleton analyses were confirmed to be de novo through parental Sanger sequencing.

RESULTS

We identified 11 de novo truncating variants in CTNNB1 in 13 patients, and two pathogenic variants, c.1867C > T (p.Gln623Ter) and c.1420C > T (p.Arg474Ter), found in two unrelated patients, respectively. Five of them were novel pathogenic variants not listed in the ClinVar database. While all patients showed varying degrees of intellectual disability, impaired motor performance, and ophthalmologic problems, none of them had structural brain abnormalities or seizure. In addition, there were three female patients who showed autistic features, such as hand stereotypy, bruxism, and abnormal breathing. A literature review revealed a female predominance of autistic features in CTNNB1-related neurodevelopmental disorder.

CONCLUSION

This is one of the largest single-center cohorts of CTNNB1-related neurodevelopmental disorder. This study investigated variable clinical features of patients and has expanded the clinical and genetic spectrum of the disease.

Exome Sequencing Reveals Novel Variants and Expands the Genetic Landscape for Congenital Microcephaly

Congenital microcephaly causes smaller than average head circumference relative to age, sex and ethnicity and is most usually associated with a variety of neurodevelopmental disorders. The underlying etiology is highly heterogeneous and can be either environmental or genetic. Disruption of any one of multiple biological processes, such as those underlying neurogenesis, cell cycle and division, DNA repair or transcription regulation, can result in microcephaly. This etiological heterogeneity manifests in a clinical variability and presents a major diagnostic and therapeutic challenge, leaving an unacceptably large proportion of over half of microcephaly patients without molecular diagnosis. To elucidate the clinical and genetic landscapes of congenital microcephaly, we sequenced the exomes of 191 clinically diagnosed patients with microcephaly as one of the features. We established a molecular basis for microcephaly in 71 patients (37%), and detected novel variants in five high confidence candidate genes previously unassociated with this condition. We report a large number of patients with mutations in tubulin-related genes in our cohort as well as higher incidence of pathogenic mutations in MCPH genes. Our study expands the phenotypic and genetic landscape of microcephaly, facilitating differential clinical diagnoses for disorders associated with most commonly disrupted genes in our cohort.

CTNNB1-related neurodevelopmental disorder in a Chinese population: A case series

CTNNB1-related disorder is an autosomal dominant neurodevelopmental disorder characterized by a variable degree of cognitive impairment, microcephaly, truncal hypotonia, peripheral spasticity, visual defects, and dysmorphic features. In this case series, we report the clinical and molecular findings of nine Chinese patients affected by CTNNB1-related disorders. The facial features of these affected individuals appear to resemble what had been previously described, with thin upper lip (77.8%) and hypoplastic alae nasi (77.8%) being the most common. Frequently reported clinical characteristics in our cohort include developmental delay (100%), peripheral spasticity (88.9%), truncal hypotonia (66.7%), microcephaly (66.7%), and dystonia (44.4%). While various eye manifestations were reported, two affected individuals (22.2%) in our cohort had familial exudative vitreoretinopathy. One of the affected individuals had craniosynostosis, a feature not reported in the literature before. To our knowledge, this is the first reported Chinese case series of CTNNB1-related neurodevelopmental disorders. Further studies are required to look into whether ethnic differences play a role in phenotypic variations.