Identification of a novel and functional mutation in the TBX5 gene in a patient by screening from 354 patients with isolated ventricular septal defect

Ventricular septal defect (VSD) is the most frequently occurring congenital heart disease in newborns. A number of genetic studies have linked TBX5 mutations to cardiac abnormalities. We aimed to identify potential pathogenic mutations in TBX5 and to provide insights into the etiology of sporadic and isolated VSD. Case-control mutational and functional analyses were performed in 354 sporadic patients with isolated VSD and 341 controls. All the coding exons and intron-exon boundaries of TBX5 were first sequenced in a group of VSD patients and controls. Sanger sequencing with high-resolution melting (HRM) curve analysis in new patients and controls was then used to detect TBX5 mutation and frequency. Luciferase activities were measured to identify transcriptional regulation of TBX5 to MYH6 and ANF promoter. A novel heterozygous missense mutations c.40C > A (p.Pro14Thr) was identified in TBX5 gene exon-2, resulting proline to threonine substitution. TBX5 containing mutation reduced transcriptional activities of the MYH6 promoter but enhanced transcriptional activities of the ANF promoter, compared with the wild type. This novel heterozygous missense mutation in TBX5 gene exon-2 that causes significant changes of the activity of TBX5 is therefore highly possible to be the cause of the defect in the VSD patients.