The T-box family transcription factor gene TBX20 acts in a conserved regulatory network, guiding heart formation and patterning in diverse species. Mouse Tbx20 is expressed in cardiac progenitor cells, differentiating cardiomyocytes, and developing valvular tissue, and its deletion or RNA interference-mediated knockdown is catastrophic for heart development. TBX20 interacts physically, functionally, and genetically with other cardiac transcription factors, including NKX2-5, GATA4, and TBX5, mutations of which cause congenital heart disease (CHD). Here, we report nonsense (Q195X) and missense (I152M) germline mutations within the T-box DNA-binding domain of human TBX20 that were associated with a family history of CHD and a complex spectrum of developmental anomalies, including defects in septation, chamber growth, and valvulogenesis. Biophysical characterization of wild-type and mutant proteins indicated how the missense mutation disrupts the structure and function of the TBX20 T-box. Dilated cardiomyopathy was a feature of the TBX20 mutant phenotype in humans and mice, suggesting that mutations in developmental transcription factors can provide a sensitized template for adult-onset heart disease. Our findings are the first to link TBX20 mutations to human pathology. They provide insights into how mutation of different genes in an interactive regulatory circuit lead to diverse clinical phenotypes, with implications for diagnosis, genetic screening, and patient follow-up.

Spondylocostal dysostosis (SCD) is an inherited disorder that is characterized by the presence of extensive hemivertebrae, truncal shortening and abnormally aligned ribs. It arises during embryonic development by a disruption of formation of somites (the precursor tissue of the vertebrae, ribs and associated tendons and muscles). Previously, three genes causing a subset of autosomal recessive forms of this disease have been identified: DLL3 (SCDO1: MIM 277300), MESP2 (SCDO2: MIM 608681) and LFNG (SCDO3: MIM609813). These genes are all important components of the Notch signaling pathway, which has multiple roles in development and disease. Here we have used autozygosity mapping to identify a mutation in a fourth Notch pathway gene, Hairy-and-Enhancer-of-Split-7 (HES7), in an autosomal recessive SCD family. HES7 encodes a bHLH-Orange domain transcriptional repressor protein that is both a direct target of the Notch signaling pathway, and part of a negative feedback mechanism required to attenuate Notch signaling. A missense mutation was identified in the DNA-binding domain of the HES7 protein. Functional analysis revealed that the mutant HES7 was not able to repress gene expression by DNA binding or protein heterodimerization. This is the first report of mutation in the human HES7 gene, and provides further evidence for the importance of the Notch signaling pathway in the correct patterning of the axial skeleton.

Familial ASD is a genetically heterogeneous disorder; one disease gene maps to chromosome 5p. Recognition of the heritable basis of familial ASD is complicated by low disease penetrance and variable expressivity. Identification of ASD or other congenital heart defects in more than one family member should prompt clinical evaluation of all relatives.