We have previously performed a comprehensive genotype/phenotype analysis on 110 patients with 11q- (Jacobsen syndrome). We determined that many of the most common congenital heart defects that occur in the general population occur in 11q-. Fifty-six percent of 11q- patients had congenital heart disease, and there was no correlation between the size of deletion and the presence of, or type of, congenital heart defect. In that study, we defined a 7 Mb cardiac ‘critical region’ that contains a putative disease-causing gene(s) for congenital heart defects. This region contains over 40 annotated genes.
In the present study, we performed high resolution chromosomal micoarray mapping on three recently identified patients with the 11q- clinical phenotype, including congenital heart defects, that have interstitial deletions overlapping the previously defined 7 Mb cardiac critical region. Based on our human genetics data, previous functional studies and the absence of heart defects in FLI-1 mutant mice, we propose ETS-1 as a candidate gene for causing at least a subset of the congenital heart defects that occur in 11q-.
Recently, Tyson et al
) proposed a potential 1.57 Mb cardiac critical region in distal 11q that is telomeric to ETS-1
. This hypothesis was based on two patients with interstitial deletions in distal 11q that did not have congenital heart disease, but overlapped the interstitial deletion of a patient with double outlet right ventricle that we described previously (JS2) (28
). Given the incomplete penetrance for congenital heart disease in 11q-, we propose that only deletions from patients with congenital heart defects should define the cardiac critical region, as we describe in the present study. In addition, Bernaciak et al
) recently described four patients with some features of 11q- that have the smallest 11q terminal deletion reported to date, 5 Mb. These deletions overlapped the critical region proposed by Tyson et al
. None of these patients had congenital heart defects, consistent with our model for a more centromeric location for the cardiac critical region. Our refined cardiac critical region also does not contain JAM-3
, a gene proposed previously as a candidate gene for causing heart defects in 11q- (30
). Consistent with this, we have recently demonstrated that JAM-C
knockout mice do not have structural heart defects (31
Phenotypic analysis of gene-targeted ETS-1
knockout mice demonstrated that deletion of ETS-1
in a pure C57/B6 background caused, with high penetrance, large membranous ventricular septal defects and frequently an abnormal-appearing ventricular morphology characterized by a bifid apex. The appearance of a bifid apex in the ETS-1 null mice has been described previously as a normal transient finding during early murine and human heart development. However, persistence of a bifid apex through later stages of heart development is indicative of an arrest of normal ventricular development (32
). In addition, a subset of the ETS-1
null mice (2/9) had a non-apex-forming left ventricle, one of the hallmarks of HLHS, although the other structures usually affected in HLHS were normal. Taken together, these results implicate a role for ETS-1 in ventricular development. The presence of a cardiac phenotype was dependent on the genetic background, paralleling what occurs in 11q- patients.
High et al
) have demonstrated that impaired differentiation of the neural crest during cardiac development in mice causes ventricular septal defects. Consistent with this model, our studies indicate that ETS-1
is expressed in the neural crest, and suggest that the loss of ETS-1
in the neural crest causes ventricular septal defects. In further support of a role for ETS-1 in the neural crest during development, we have observed hypopigmentation in the fur of ETS-1 heterozygotes (Supplementary Material, Fig. S1
). This is similar to what has been described in mice carrying the splotch
mutation of PAX-3, a gene that is essential for neural crest function during development (35
The role of ETS-1 in the endocardium during heart development is unclear. Because ETS-1 expression was not detected in the myocardium, one possibility is that ETS-1 is required in the endocardium for normal myocardial development through a non-cell autonomous mechanism. Alternatively, it is possible that the loss of ETS-1 in the vascular endothelium causes congenital heart defects secondary to impaired hemodynamics during heart development.
In summary, our studies implicate an important role for ETS-1 in human heart development and in the etiology of some of the most common congenital heart defects. Future studies will be aimed at defining the genetic pathways and developmental lineages involving ETS-1 in normal heart development, and how decreased ETS-1 function causes human congenital heart defects.