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Simple Summary: Atrial fibrillation (AF), the most prevalent sustained dysrhythmia, is accountable for substantial mortality and morbidity. Accumulating convincing evidence highlights the predominant roles of heritable components in the initiation and maintenance of AF. Here, through pan-genomic genotyping with genetic markers followed by a genetic linkage study in an AF family, a novel AF-causing locus was located at human chromosome 7p14.2–p14.3. An exome-wide sequence assay unveiled that, at the defined locus, the mutation in TBX20, NM_001077653.2: c.695A>G; p.(His232Arg), was solely co-segregated with AF in the family. Additionally, a Sanger sequencing assay of TBX20 in another AF family uncovered a novel mutation, NM_001077653.2: c.862G>C; p.(Asp288His). Neither of the two mutations were found in 600 control persons. Functional investigations demonstrated that the two mutations both significantly reduced the transactivation of the target gene KCNH2 and the ability to bind the promoter of KCNH2, while they had no effect on the nuclear distribution of TBX20. These findings strongly indicate that TBX20 is a new AF-predisposing gene, shedding light on the mechanism underlying AF and suggesting clinical significance for the individually tailored treatment of AF. Atrial fibrillation (AF), the most prevalent type of sustained cardiac dysrhythmia globally, confers strikingly enhanced risks for cognitive dysfunction, stroke, chronic cardiac failure, and sudden cardiovascular demise. Aggregating studies underscore the crucial roles of inherited determinants in the occurrence and perpetuation of AF. However, due to conspicuous genetic heterogeneity, the inherited defects accounting for AF remain largely indefinite. Here, via whole-genome genotyping with genetic markers and a linkage assay in a family suffering from AF, a new AF-causative locus was located at human chromosome 7p14.2-p14.3, a ~4.89 cM (~4.43-Mb) interval between the markers D7S526 and D7S2250. An exome-wide sequencing assay unveiled that, at the defined locus, the mutation in the TBX20 gene, NM_001077653.2: c.695A>G; p.(His232Arg), was solely co-segregated with AF in the family. Additionally, a Sanger sequencing assay of TBX20 in another family suffering from AF uncovered a novel mutation, NM_001077653.2: c.862G>C; p.(Asp288His). Neither of the two mutations were observed in 600 unrelated control individuals. Functional investigations demonstrated that the two mutations both significantly reduced the transactivation of the target gene KCNH2 (a well-established AF-causing gene) and the ability to bind the promoter of KCNH2, while they had no effect on the nuclear distribution of TBX20. Conclusively, these findings reveal a new AF-causative locus at human chromosome 7p14.2-p14.3 and strongly indicate TBX20 as a novel AF-predisposing gene, shedding light on the mechanism underlying AF and suggesting clinical significance for the allele-specific treatment of AF patients. [ABSTRACT FROM AUTHOR]

Simple Summary: Congenital heart disease is associated with substantial mortality and morbidity as well as socioeconomic burden, and increasing research underscores the genetic basis for it. In this study, a genome-wide genotyping with microsatellite markers followed by linkage analysis was performed in a Chinese family suffering congenital heart disease and arrhythmias, and a novel genetic locus linked to the disease was located on chromosome 17q21.31-q21.33. Sequencing assays of the candidate genes at the locus revealed a novel heterozygous mutation in the GJC1 gene coding for Cx45, NM_005497.4:c.550A>G;p.R184G, which was in co-segregation with the disease in the whole family and was not detected in 516 control individuals. Electrophysiological analyses showed that the mutation significantly diminished the coupling conductance in homomeric cell pairs (R184G/R184G) and in cell pairs expressing R184G/Cx45 or R184G/Cx43, in a dominant-negative mode. Fluorescent dye uptake experiments demonstrated no apparent change of the R184G mutation on the Cx45 hemichannels. These findings define a new genetic locus for congenital heart disease and arrhythmias on chromosome 17q21.31-q21.33 and indicate GJC1 as a new gene predisposing to the disease. As the most prevalent type of birth malformation, congenital heart disease (CHD) gives rise to substantial mortality and morbidity as well as a socioeconomic burden. Although aggregating investigations highlight the genetic basis for CHD, the genetic determinants underpinning CHD remain largely obscure. In this research, a Chinese family suffering from autosomal dominant CHD (atrial septal defect) and arrhythmias was enrolled. A genome-wide genotyping with microsatellite markers followed by linkage assay as well as sequencing analysis was conducted. The functional effects of the discovered genetic mutation were characterized by dual patch-clamp electrophysiological recordings in N2A cells and propidium iodide uptake assays in HeLa cells. As a result, a novel genetic locus for CHD and arrhythmias was located on chromosome 17q21.31-q21.33, a 4.82-cM (5.12 Mb) region between two markers of D17S1861 and D17S1795. Sequencing assays of the genes at the mapped locus unveiled a novel heterozygous mutation in the GJC1 gene coding for connexin 45 (Cx45), NM_005497.4:c.550A>G;p.R184G, which was in co-segregation with the disease in the whole family and was not observed in 516 unrelated healthy individuals or gnomAD. Electrophysiological analyses revealed that the mutation significantly diminished the coupling conductance in homomeric cell pairs (R184G/R184G) and in cell pairs expressing either R184G/Cx45 or R184G/Cx43. Propidium iodide uptake experiments demonstrated that the Cx45 R184G mutation did not increase the Cx45 hemichannel function. This investigation locates a new genetic locus linked to CHD and arrhythmias on chromosome 17q21.31-q21.33 and indicates GJC1 as a novel gene predisposing to CHD and arrhythmias, implying clinical implications for prognostic risk assessment and personalized management of patients affected with CHD and arrhythmias. [ABSTRACT FROM AUTHOR]