Dr. Gary Gibbons, Director, NHLBI:  Obviously, your most recent work recently published in Nature is very exciting. We’re all aware of the fact that congenital heart disease is the most common birth defect. And your group, the team has contributed significantly to our understanding with this intriguing insight that a substantial proportion, perhaps 10% of these children with congenital heart disease may arise related to spontaneous mutations. Could you just briefly summarize what are the key findings of your most recent publication?

Dr. Richard Lifton, Yale University:  Sure. So as you note, congenital heart disease is a prevalent disorder. It is very common and many of the severe forms of congenital heart disease severely impact children’s lives. So it’s an important public health problem and we’ve known very little about the fundamental causes of this disease.

So in the context of the Pediatric Cardiac Genetics Consortium, which is a group of investigators from many institutions across the country, we’ve collected a large cohort of patients with congenital heart disease. And one of the projects that we took on in this context was to ask the question whether new mutations that are absent in parents but present in their affected offspring with congenital heart disease, whether these new mutations might contribute to the causes of congenital heart disease. And one of the reasons to think that that might be the case is that these diseases, until the development of cardiac bypass surgery, were frequently either lethal or prevented children from growing up to adulthood and passing on their genes to subsequent generations. So we thought there might be reason that new mutations might play a role.

So we tested that by using the new technology for sequencing all of the genes in the genome and sequenced the parents and their affected offspring with severe congenital heart disease and look at the spectrum of mutations in the affected patients compared to healthy offspring from different unaffected parents. And the result was that at least 10% of cases of severe congenital heart disease across a wide spectrum of the types of congenital heart disease abnormalities, about 10% of these cases appear to be attributable to these new mutations. Which for the first time, establishes that rare de novo mutations, new mutations not present in the parents, play a significant role in the cause of these diseases.

Dr. Gibbons:  That’s very exciting. This is sort of leading edge discovery science and often when we’re doing these things, we’re often even surprised ourselves by some of the findings. Was there anything particularly intriguing or surprising to you about what you discovered, the loci, etc.?

Dr. Lifton:  Sure. So probably that the most exciting finding coming out of the work, aside from the general role of new mutations, is that we found a particular group of genes that are mutated more frequently and they suggest past causation of these diseases that we think is quite interesting. In particular, these genes are genes whose encoded protein products are involved in modifying histone proteins. So DNA in the nucleus is wrapped around a core of histone proteins and for a long time, it was thought that these proteins are just kind of the inert packing material that DNA is wrapped around and it’s relatively biologically inert. But over the last 15 years or so, it’s become clear that the histones are actually involved in regulating which genes are available for expression at different developmental times. And we found specific modifications of histone H3, one of the histones that DNA is wrapped around, that mutations that affect addition of the methyl group at a single position in histone H3 is a frequent pathway for mutation in these children. And that maybe about 3% of all of the patients that we studied have mutation in genes that were involved in introducing this methyl mark, removing the methyl mark, reading the methyl mark, or other genes that regulated the production of this methyl mark. 

And the reason that that is so interesting is that that pathway has been recognized to play an important role previously in development in model systems like flies and worms and fish and so forth. And this now links it clearly to congenital heart disease, which we think is very interesting and it sets the stage for a lot of further biology and understanding of how pathogenesis actually works at a very molecular detail. 

Dr. Gibbons:  I agree, that was a very intriguing observation in the study. And I’m sure you’ve thought about this, it obviously wasn’t captured within the context of this particular report, but as you’ve pointed out that those changes in those methylation patterns, in some context, can be responsive to environmental factors. Does that suggest that there’s something in the in utero environment or other context that might be modulating some of these observations you’re making in some way?

Dr. Lifton:  So that’s a key question that this work poses as a consequence of the results. So one of the surprising observations was that we had mutations that just altered the function of one copy of many of the genes in this pathway and that we had mutations that affected the addition of the methyl group but also, mutations that affected the removal of the methyl group. And what that suggests is that subtle changes in the levels of methylation, either up or down, might be changing the overall readout of a program involved in heart development. And that then, as you allude to, raises the possibility that environmental perturbations without an underlying genetic change could affect that same biological pathway.

And you know, there’s some reason to think that there might be environmental agents that could affect this. And as you know, we now recognize, for example, that neural tube defects can be ameliorated, can be prevented in a significant fraction of patients by addition of folate to the diet of women before they become pregnant. And I think that places on the radar screen the possibility that a range of congenital abnormalities might be prevented by changing features in the diet or aspects of the environment and trying to follow that out, obviously, will be one of the major challenges in thinking about how to prevent congenital heart diseases.
SEGMENT 1: Dr. Gibbons and Dr. Lifton Q&A Transcript
May 29, 2013