Mutations in cardiac transcription factors have been implicated as genetic etiologies of human CHD (22
). We have identified two rare GATA6
sequence variants, in a subset of individuals with CHD, which resulted in non-synonymous amino acid substitutions in two subjects after screening a population of 310 affected individuals. In vitro transactivation studies demonstrated that the GATA6 A178V variant is a gain-of-function mutation with increased transactivation ability when compared to wildtype GATA6. These findings highlight the importance of the GATA6
as an etiologic gene for a subset of CHD and suggest that appropriate levels of GATA6 are critical for normal heart development in humans.
The prevalence of GATA6
sequence variants in our study was 0.6%, consistent with similar large population based studies of non-familial CHD where the mutation prevalence of a single CHD-causing gene is less than 2% (5
). The report by Kodo, et al. identified two GATA6
mutations in a population of 21 individuals with truncus arteriosus (16
). Interestingly, we did not identify any GATA6
mutations in 12 subjects with truncus arteriosus. However, we did identify a gain-of-function mutation in an individual with tetralogy of Fallot, which is embryologically related to truncus arteriosus. Therefore, it is possible that the prevalence of GATA6
mutations is higher in a population of subjects with conotruncal abnormalities. In our study, this would represent an incidence of 2% (1/45). Of note, the gain-of-function GATA6
A178V mutation was inherited from an unaffected parent. The finding of incomplete penetrance has been most recently shown with NOTCH1
variants, which exhibit in vitro functional deficits, and were identified in individuals with left-sided cardiac malformations and their unaffected parents (24
). For the L198V variant we did not identify any in vitro functional abnormalities in the assays that we utilized. The nucleotide variant is rare and alters a highly conserved leucine residue and ultimately, biochemical deficits may exist in transactivation assays with other luciferase reporters or protein-protein interactions due to alterations in structure.
Normal cardiac development requires adequate gene dosage of cardiac transcription factors. This has been shown in both murine and human studies and classic examples include NKX2-5
, and TBX1
where loss-of-function mutations disrupt cardiac morphogenesis in humans and mice (25
). Previous studies suggest that increased dosage of TBX5
is associated with phenotypes consistent with Holt-Oram syndrome and Shprintzen syndrome, respectively, while a gain-of-function mutation in TBX20
was recently reported to be associated with atrial septal defects and cardiac valve defects (26
). Additionally, gain-of-function mutations in PTPN11
have been well described to be associated with the cardiac defects found in Noonan syndrome (29
). Our in vitro studies suggest that the GATA6
A178V sequence variant represents a gain-of-function mutation with its increased transactivation ability. Consistent with this, the alanine is located within a polyalanine tract, which has been proposed to function as a transcriptional repression domain (30
). This finding is particularly interesting in light of studies in Xenopus which have demonstrated that overexpression of GATA-6 disrupts cardiac development by preventing differentiation and blocking expression of GATA target genes, cardiac actin and XMLC2, a heart specific myosin light chain (31
). Consistent with this, mutations in the GATA target, alpha myosin heavy chain (MYH6
) are linked to atrial septal defects in humans (32
). Further experimentation is necessary to understand the effect of this substitution on GATA6 protein structure and function during cardiac development.
In conclusion, genetic abnormalities involving cardiac development genes are increasingly being discovered to be associated with CHD in humans. In this study, we have identified two novel sequence variations in the cardiac transcription factor, GATA6, to be associated with CHD and similar to other investigations, genetic variants of single gene are associated with only a small subset of CHD. Studies of larger well-phenotyped populations will need to be performed for improved genotype-phenotype correlations and determine if GATA6 mutations are found in a higher frequency with cardiac septal defects and conotruncal abnormalities. Ultimately, further studies elucidating the role of GATA6 in the developing cardiovascular system will be required to increase our knowledge of the genetic basis of CHD and to provide more personalized genetic counseling and develop novel preventive therapies.