A single nucleotide deletion resulting in a frameshift in exon 4 of TAB2 is associated with a polyvalular syndrome

Growth restriction and congenital heart disease caused by a novel TAB2 mutation: A case report

Congenital heart disease (CHD) is a malformation present from birth caused by the abnormal development of the heart and large blood vessels during the prenatal development. The TGF-β activated kinase 1 (MAP3K7) binding protein 2 (TAB2) gene plays an important role in the embryonic development of heart tissue. When haploid dosage is insufficient, it can lead to CHD or cardiomyopathy. The present study reported a case study of a Chinese child with growth restriction and CHD. The results of whole exome sequencing suggested that a novel frameshift mutation (c.1056delC/p.Ser353fsTer8) occurred in TAB2. The parents of this patient are wild-type at this locus; therefore, it may be a de novo mutation. The mutant plasmid was constructed in vitro, and the western blotting results showed that the mutation may cease protein expression. This indicated the pathogenic harmfulness of this mutation. In conclusion, the present study emphasizes that TAB2 defects should be investigated in patients with unexplained short stature and CHD, irrespective of family history regarding CHD or cardiomyopathy. The current study provided new data on the mutation spectrum and provided information for second pregnancies and genetic counseling of the parents of patients.

Expanding the phenotype of TAB2 variants and literature review

TAB2 is a gene located on chromosome 6q25.1 and plays a key role in development of the heart. Existing literature describes congenital heart disease as a common recognized phenotype of TAB2 gene variants, with evidence of a distinct syndromic phenotype also existing beyond this. Here we describe 14 newly identified individuals with nine novel, pathogenic TAB2 variants. The majority of individuals were identified through the Deciphering Developmental Disorders study through trio whole exome sequencing. Eight individuals had de novo variants, the other six individuals were found to have maternally inherited, or likely maternally inherited, variants. Five individuals from the same family were identified following cardiac disease gene panel in the proband and subsequent targeted familial gene sequencing. The clinical features of this cohort were compared to the existing literature. Common clinical features include distinctive facial features, growth abnormalities, joint hypermobility, hypotonia, and developmental delay. Newly identified features included feeding difficulties, sleep problems, visual problems, genitourinary abnormality, and other anatomical variations. Here we report 14 new individuals, including novel TAB2 variants, in order to expand the emerging syndromic clinical phenotype and provide further genotype-phenotype correlation.

There is more to it than just congenital heart defects - The phenotypic spectrum of TAB2-related syndrome

BACKGROUND

Congenital heart defects (CHD) are the most common birth defect and disease-causing variant in TAB2 have found to be associated with isolated CHD. Recently, it became evident that pathogenic, mostly loss-of-function variants in TAB2 can also cause syndromic CHD that includes connective tissue anomalies. The number of published cases is limited posing a challenge for counseling affected patients and their relatives.

METHODS

Cases in whom whole exome sequencing was executed at our institute between January 2015 and June 2021 were screened for disease-causing variants in TAB2. Additionally, a PubMed-based review of the literature was performed in December 2021 in order to give an updated clinical overview of the TAB2-associated phenotypic spectrum, including our cases.

RESULTS

We identified three cases with syndromic CHD caused by different heterozygous loss-of-function variants in TAB2. In one of these cases, the variant was inherited by a healthy father. A comparison with published cases highlights that most patients were affected by structural and/or arrhythmic heart disease (about 90%) while about two third of all cases had syndromic comorbidity especially connective tissue defects and dysmorphic abnormalities.

CONCLUSION

Our findings indicate a variable expressivity as well as reduced penetrance of TAB2-associated CHD. Disease-causing variants in TAB2 should be considered in cases with isolated CHD but also in syndromic CHD with connective tissue abnormalities. However, prediction of the patients' clinical outcome solely based on the variant in TAB2 is still extremely challenging.

TAB2 variants cause cardiovascular heart disease, connective tissue disorder, and developmental delay

Congenital heart defects (CHD) are the most commonly occurring birth defect and can occur in isolation or with additional clinical features comprising a genetic syndrome. Autosomal dominant variants in TAB2 are recognized by the American Heart Association as causing nonsyndromic CHD, however, emerging data point to additional, extra-cardiac features associated with TAB2 variants. We identified 15 newly reported individuals with pathogenic TAB2 variants and reviewed an additional 24 subjects with TAB2 variants in the literature. Analysis showed 64% (25/39) of individuals with disease resulting from TAB2 single nucleotide variants (SNV) had syndromic CHD or adult-onset cardiomyopathy with one or more extra-cardiac features. The most commonly co-occurring features with CHD or cardiomyopathy were facial dysmorphism, skeletal and connective tissue defects and most subjects with TAB2 variants present as a connective tissue disorder. Notably, 53% (8/15) of our cohort displayed developmental delay and we suspect this may be a previously unappreciated feature of TAB2 disease. We describe the largest cohort of subjects with TAB2 SNV and show that in addition to heart disease, features across multiple systems are present in most TAB2 cases. In light of our findings, we recommend that TAB2 be included on the list of genes that cause syndromic CHD, adult-onset cardiomyopathy, and connective tissue disorder.

Loss-of-function variants in exon 4 of TAB2 cause a recognizable multisystem disorder with cardiovascular, facial, cutaneous, and musculoskeletal involvement

PURPOSE

This study aimed to describe a multisystemic disorder featuring cardiovascular, facial, musculoskeletal, and cutaneous anomalies caused by heterozygous loss-of-function variants in TAB2.

METHODS

Affected individuals were analyzed by next-generation technologies and genomic array. The presumed loss-of-function effect of identified variants was assessed by luciferase assay in cells transiently expressing TAB2 deleterious alleles. In available patients' fibroblasts, variant pathogenicity was further explored by immunoblot and osteoblast differentiation assays. The transcriptomic profile of fibroblasts was investigated by RNA sequencing.

RESULTS

A total of 11 individuals from 8 families were heterozygotes for a novel TAB2 variant. In total, 7 variants were predicted to be null alleles and 1 was a missense change. An additional subject was heterozygous for a 52 kb microdeletion involving TAB2 exons 1 to 3. Luciferase assay indicated a decreased transcriptional activation mediated by NF-κB signaling for all point variants. Immunoblot analysis showed a reduction of TAK1 phosphorylation while osteoblast differentiation was impaired. Transcriptomic analysis identified deregulation of multiple pleiotropic pathways, such as TGFβ-, Ras-MAPK-, and Wnt-signaling networks.

CONCLUSION

Our data defined a novel disorder associated with loss-of-function or, more rarely, hypomorphic alleles in a restricted linker region of TAB2. The pleiotropic manifestations in this disorder partly recapitulate the 6q25.1 (TAB2) microdeletion syndrome and deserve the definition of cardio-facial-cutaneous-articular syndrome.

TAB2 deletions and variants cause a highly recognisable syndrome with mitral valve disease, cardiomyopathy, short stature and hypermobility

Deletions that include the gene TAB2 and TAB2 loss-of-function variants have previously been associated with congenital heart defects and cardiomyopathy. However, other features, including short stature, facial dysmorphisms, connective tissue abnormalities and a variable degree of developmental delay, have only been mentioned occasionally in literature and thus far not linked to TAB2. In a large-scale, social media-based chromosome 6 study, we observed a shared phenotype in patients with a 6q25.1 deletion that includes TAB2. To confirm if this phenotype is caused by haploinsufficiency of TAB2 and to delineate a TAB2-related phenotype, we subsequently sequenced TAB2 in patients with matching phenotypes and recruited patients with pathogenic TAB2 variants detected by exome sequencing. This identified 11 patients with a deletion containing TAB2 (size 1.68-14.31 Mb) and 14 patients from six families with novel truncating TAB2 variants. Twenty (80%) patients had cardiac disease, often mitral valve defects and/or cardiomyopathy, 18 (72%) had short stature and 18 (72%) had hypermobility. Twenty patients (80%) had facial features suggestive for Noonan syndrome. No substantial phenotypic differences were noted between patients with deletions and those with intragenic variants. We then compared our patients to 45 patients from the literature. All literature patients had cardiac diseases, but syndromic features were reported infrequently. Our study shows that the phenotype in 6q25.1 deletions is caused by haploinsufficiency of TAB2 and that TAB2 is associated not just with cardiac disease, but also with a distinct phenotype, with features overlapping with Noonan syndrome. We propose the name "TAB2-related syndrome".

Integrative analysis of genomic variants reveals new associations of candidate haploinsufficient genes with congenital heart disease

Numerous genetic studies have established a role for rare genomic variants in Congenital Heart Disease (CHD) at the copy number variation (CNV) and de novo variant (DNV) level. To identify novel haploinsufficient CHD disease genes, we performed an integrative analysis of CNVs and DNVs identified in probands with CHD including cases with sporadic thoracic aortic aneurysm. We assembled CNV data from 7,958 cases and 14,082 controls and performed a gene-wise analysis of the burden of rare genomic deletions in cases versus controls. In addition, we performed variation rate testing for DNVs identified in 2,489 parent-offspring trios. Our analysis revealed 21 genes which were significantly affected by rare CNVs and/or DNVs in probands. Fourteen of these genes have previously been associated with CHD while the remaining genes (FEZ1, MYO16, ARID1B, NALCN, WAC, KDM5B and WHSC1) have only been associated in small cases series or show new associations with CHD. In addition, a systems level analysis revealed affected protein-protein interaction networks involved in Notch signaling pathway, heart morphogenesis, DNA repair and cilia/centrosome function. Taken together, this approach highlights the importance of re-analyzing existing datasets to strengthen disease association and identify novel disease genes and pathways.

Genetic association study between TAB2 polymorphisms and noise-induced-hearing-loss in a Han Chinese population

Noise-induced-hearing-loss(NIHL) is a common occupational disease caused by various environmental and biological factors. To investigate the association between TAB2 and the susceptibility of NIHL of people exposed to occupational environments, a genetic association study was performed on selected companies with 588 cases and 537 healthy control subjects. Five selected single nucleotide polymorphisms (SNPs) in TAB2,incoluding rs2744434, rs521845, rs652921, rs7896, rs9485372, were genotyped after a collection of DNA samples. Evident differences in participants between the case group and the control group reveals the result that people with the TAB2 has a high probability of getting NIHL. The results show that rs521845 is deeply associated with the risk of NIHL and is available for the diagnosis in the future.

SOX17 loss-of-function variation underlying familial congenital heart disease

As the most prevalent form of human birth defect, congenital heart disease (CHD) contributes to substantial morbidity, mortality and socioeconomic burden worldwide. Aggregating evidence has convincingly demonstrated that genetic defects exert a pivotal role in the pathogenesis of CHD, and causative mutations in multiple genes have been causally linked to CHD. Nevertheless, CHD is of pronounced genetic heterogeneity, and the genetic components underpinning CHD in the overwhelming majority of patients remain obscure. In this research, a four-generation consanguineous family suffering from CHD transmitted in an autosomal dominant mode was recruited. By whole-exome sequencing and bioinformatics analyses as well as Sanger sequencing analyses of the family members, a new heterozygous SOX17 variation, NM_022454.4: c.553G > T; p.(Glu185*), was identified to co-segregate with CHD in the family, with complete penetrance. The nonsense variation was neither detected in 310 unrelated healthy volunteers used as controls nor retrieved in such population genetics databases as the Exome Aggregation Consortium database, Genome Aggregation Database, and the Single Nucleotide Polymorphism database. Functional assays by utilizing a dual-luciferase reporter assay system unveiled that the Glu185*-mutant SOX17 protein had no transcriptional activity on its two target genes NOTCH1 and GATA4, which have been reported to cause CHD. Furthermore, the mutation abrogated the synergistic transactivation between SOX17 and NKX2.5, another established CHD-causing transcription factor. These findings firstly indicate SOX17 loss-of-function mutation predisposes to familial CHD, which adds novel insight to the molecular mechanism of CHD, implying potential implications for genetic risk appraisal and individualized prophylaxis of the family members affected with CHD.