Mutations in the cardiac transcription factor NKX2.5 affect diverse cardiac developmental pathways

Abstract

Heterozygous mutations in NKX2.5, a homeobox transcription factor, were reported to cause secundum atrial septal defects and result in atrioventricular (AV) conduction block during postnatal life. To further characterize the role of NKX2.5 in cardiac morphogenesis, we sought additional mutations in groups of probands with cardiac anomalies and first-degree AV block, idiopathic AV block, or tetralogy of Fallot. We identified 7 novel mutations by sequence analysis of the NKX2.5-coding region in 26 individuals. Associated phenotypes included AV block, which was the primary manifestation of cardiac disease in nearly a quarter of affected individuals, as well as atrial septal defect and ventricular septal defect. Ventricular septal defect was associated with tetralogy of Fallot or double-outlet right ventricle in 3 individuals. Ebstein's anomaly and other tricuspid valve abnormalities were also present. Mutations in human NKX2.5 cause a variety of cardiac anomalies and may account for a clinically significant portion of tetralogy of Fallot and idiopathic AV block. The coinheritance of NKX2.5 mutations with various congenital heart defects suggests that this transcription factor contributes to diverse cardiac developmental pathways.

Figure 1

Pedigree of familial congenital heart disease. The mutation found in each family is shown under the pedigree identification. Men are denoted by squares, women by circles. Closed symbols denote individuals with a NKX2.5 mutation. To illustrate variation in phenotype, the symbol is divided into quadrants indicating the presence of AV block, ASD, VSD, or tricuspid valve (TV) abnormality (including Ebstein’s anomaly). Open symbols denote normal genotype. Hatched symbols denote individuals with unknown genotype status.

Figure 2

Echocardiogram/Doppler showing secundum ASD and posterior muscular VSD (BEA III-2). Subcostal view shows large secundum ASD (left). The parasternal short axis view shows posterior muscular VSD with left ventricle to right ventricle blood flow on color Doppler interrogation (right). The VSD spontaneously closed during the first 6 months of life; the ASD was surgically closed at 10 months of age. LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.

Figure 3

Echocardiogram and ECG characteristics of Ebstein’s anomaly (BET III-2). (a) Four chamber echocardiogram during diastole (left) and systole (right); arrows indicate location of tricuspid and mitral valve (left and right). A sail-like anterior tricuspid valve leaflet is evident in diastole; inferior displacement of the septal leaflet is evident in systole. RA, right atrium; RV, right ventricle; LV, left ventricle. (b) ECG shows first-degree AV block and right bundle branch block (bottom).

Figure 4

Diagram of the NKX2.5 gene showing 10 heterozygote mutations. Three mutations were reported previously (Gln170ter, Thr178Met, Gln198ter) (19). The region enclosed by boxes indicates exon 1 (left) and exon 2 (right); the horizontal line indicates the intron. Shaded boxes indicate the 5′ and 3′ untranslated regions (UTR), respectively. The white box denotes the coding region, and the black boxes indicate the conserved TN domain, homeodomain (HD), and NK domain, respectively, within the coding region. Nonsense mutations are indicated above and missense mutations below the gene diagram.