Systematic survey of variants in TBX1 in non-syndromic tetralogy of Fallot identifies a novel 57 base pair deletion that reduces transcriptional activity but finds no evidence for association with common variants

Abstract

BackgroundTetralogy of Fallot (TOF) is common in individuals with hemizygous deletions of chromosome 22q11.2 that remove the cardiac transcription factor TBX1.ObjectiveTo assess the contribution of common and rare TBX1 genetic variants to TOF.DesignRare TBX1 variants were sought by resequencing coding exons and splice-site boundaries. Common TBX1 variants were investigated by genotyping 20 haplotype-tagging SNPs capturing all the common variations present at the locus. Association analysis was performed using the program UNPHASED.PatientsTBX1 exons were sequenced in 93 patients with non-syndromic TOF. Single nucleotide polymorphism analysis was performed in 356 patients with TOF, their parents and healthy controls.ResultsThree novel variants not present in 1000 chromosomes from healthy ethnically matched controls were identified. One of these variants, an in-frame 57 base-pair deletion in the third exon which removed 19 evolutionarily conserved residues, decreased transcriptional activity by 40% in a dual luciferase assay (p=0.008). Protein expression studies demonstrated that this mutation affected TBX1 protein stability. After correction for multiple comparisons, no significant associations between common genetic variants and TOF susceptibility were found.ConclusionThis study demonstrates that rare TBX1 variants with functional consequences are present in a small proportion of non-syndromic TOF.

TBX1 loss‑of‑function mutation contributes to congenital conotruncal defects

“…This expectation was in accordance with the experimental data, which indicated that the mutant exhibited significantly reduced transactivation activity. This diminished transcriptional activation supports a previous hypothesis that normal cardiovascular development is particularly susceptible to differences in TBX1 activity and a hypomorphic allele may predispose non-syndromic CHD (54).…”

“…However, an increasing number of TBX1 (54) screened TBX1 in 93 TOF probands with had no known chromosomal abnormalities or other recognized syndromes. Two non-synonymous mutations in two probands, including the amino acid substitution p.G39S in a proband with TOF and the in-frame amino acid deletion p.P43_P61del in a proband with TOF as well as a right-sided aortic arch were identified, with a mutational prevalence of ~2.15%.…”

“…Heterozygous TBX1-null mice exhibit cardiac, craniofacial, thymic and parathyroid deformities, similar to those observed in patients with severe 22q11DS (50)(51)(52). In addition to syndromic CTD, TBX1 mutations have been causally linked to non-syndromic CTD in humans, including isolated TOF, VSD, PA, DORV, IAA and aortic arch anomalies (4,(53)(54)(55). However, the prevalence and spectrum of TBX1 mutations in patients with other forms of non-syndromic CTD remain unknown.…”

“…The aim of the present study was to evaluate the prevalence and spectrum of TBX1 mutations in a cohort of patients with isolated CTD and characterize the functional effect of an identified TBX1 mutation associated with CTD. (54,55) and samples with deletions were excluded from further analysis. During a period from September 2014 to January 2016, a total of 300 healthy individuals (178 male, 122 female; median age, 2.4 years old), matched with the patients in age, sex and ethnicity, were enrolled as controls from the above-mentioned institutions where the CTD patients were recruited.…”

Mutation Analysis of TBX1 in Children with Conotruncal Heart Anomalies

“…However, no pathogenic mutations or sequence variants of TBX1 were detected in the patients and healthy controls. While this is in agreement with the report by Conti et al [1], it is also in contrast with a few studies that have documented either mutations or polymorphisms in TBX1 associated with isolated CTA [2][3][4][5]. Our results, though negative, provide corroborative evidence that TBX1 mutations may not be associated with CTA in the selected pediatric population.…”