A novel HAND2 loss-of-function mutation responsible for tetralogy of Fallot

Abstract

Congenital heart disease (CHD), the most common type of developmental abnormality, is associated with substantial morbidity and mortality in humans worldwide. The basic helix-loop-helix transcription factor, heart and neural crest derivatives expressed 2 (HAND2), has been demonstrated to be crucial for normal cardiovascular development in animal models. However, whether a genetically defective HAND2 contributes to congenital heart disease (CHD) in humans remains to be explored. In this study, the entire coding region and splicing boundaries of the HAND2 gene were sequenced in a cohort of 145 unrelated patients with CHD. A total of 200 unrelated, ethnically-matched healthy individuals used as controls were also genotyped for HAND2. The functional effect of the mutant HAND2 was characterized in contrast to its wild-type counterpart by using a dual-luciferase reporter assay system. As a result, a novel heterozygous HAND2 mutation, p.L47P, was identified in a patient with tetralogy of Fallot (TOF). The misense mutation, which altered the amino acid conserved evolutionarily among species, was absent in 400 control chromosomes. Functional analyses unveiled that the mutant HAND2 had a significantly decreased transcriptional activity. Furthermore, the mutation markedly reduced the synergistic activation between HAND2 and GATA4 or NKX2.5, other two cardiac key transcription factors involved in the pathogenesis of CHD. To the best of our knowledge, this study is the first to report the association of a HAND2 loss-of-function mutation with an increased vulnerability to TOF in humans, which provides novel insight into the molecular mechanism underpinning CHD, suggesting potential implications for the genetic counseling of families with CHD.

Haploinsufficiency of the basic helix–loop–helix transcription factorHAND2causes congenital heart defects

“…The clinical significance of this paternally inherited deletion was supported by the paternal family history of CHDs. This informative case adds to the previously reported CHD patients with heterozygous HAND2 sequence variants (Table 1) (Liu et al, 2018; Lu et al, 2016; Shen et al, 2010; Sun et al, 2016; Topf et al, 2014) and directly supports haploinsufficiency of HAND2 as a pathogenic Mendelian cause of CHD formation.…”

“…The two‐exon human HAND2 gene has been associated with CHDs through the recent identification of heterozygous HAND2 sequence variants among selected patients with ToF, patent ductus arteriosis, pulmonary atresia, pulmonary stenosis, atrial or ventricular septal defect, double outlet right ventricle, and dilated cardiomyopathy (Liu et al, 2018; Lu et al, 2016; Shen et al, 2010; Sun et al, 2016; Topf et al, 2014). These reported HAND2 variants include missense, truncating, and small duplication alleles (Table 1), which together suggest a potential loss‐of‐function role in CHD formation.…”

“…Notably, the murine heart and neural crest derivatives expressed 2 ( Hand2 ) gene encodes a basic helix–loop–helix (bHLH) TF that, together with Hand1 , has an established role in murine cardiogenesis (George & Firulli, 2019). The significance of HAND2 in heart development is further supported by the recent identification of heterozygous HAND2 variants in some patients with CHDs (Table 1) (Liu et al, 2018; Lu et al, 2016; Shen et al, 2010; Sun et al, 2016; Topf et al, 2014); however, HAND2 has yet to be established as a Mendelian CHD gene. Here we report a 31‐month‐old male with significant CHDs and a heterozygous 546.0‐kb deletion that includes exons 1 and 2 of SCRG1 , HAND2 , and the neighboring noncoding HAND2‐AS1 .…”

A HAND to TBX5 Explains the Link Between Thalidomide and Cardiac Diseases

“…Whereas the recent article by Lu CX et al . does suggest a direct link between the p.L47P HAND2 variant and TOF 66 , we suggest that our p.G202V variant doesn’t contribute to all four phenotypes observed in Tetralogy of Fallot, but rather contribute to at least one of them probably the one pertaining to the overriding aorta, since the same variant is also found in both patients with CoA and aortic stenosis (Supplementary Table 1). In addition, the presence of the variants in a couple of healthy individuals argues for a partial penetrance pattern of inheritance, although some of those individuals are young and may suffer from aortic stenosis later on or even succumb to early myocardial infarcts.…”

“…The p.G202V variant in HAND2 is the first variant that affects a conserved region in the C-terminal part of the protein leading to a transcriptionally inactive protein. Besides four reports, two of them published recently, there is no genetic data linking HAND2 variants to congenital diseases 63–66 . Our results suggest a strong association of the p.G202V variant with the TOF and aortic malformations phenotypes, but not with the VSD phenotype (Supplementary Table 1 and Fig.…”