Preventing birth defects - An interview with Professor Sally Dunwoodie

Head of Victor Chang Cardiac Research Institute's Embryology Laboratory talks congenital heart disease research, the team's discoveries and where to next

28 Dec 2023

Professor Sally Dunwoodie has always been fascinated by those earliest stages of human development.

It involves a vast number of chemical reactions and cellular movements coming together at the right time and the right place to form a perfectly functioning embryo. It's a process she describes as phenomenal, but it’s one that can often go terribly wrong with millions of children being born around the world every year with birth defects.

Professor Dunwoodie has made it her life’s work to focus on congenital heart disease (CHD) which affect around one in every 100 live born babies.

She’s now working on a potential new treatment which could help prevent many cases of CHD and some recurrent miscarriages too.

What made you focus on CHD?

I had started researching embryo development as a post-doc in London but found that hardly anyone was working on heart development. When I had the chance to join the Victor Chang Cardiac Research Institute in 2000, I decided that would be my area of focus and that led me to birth defects.

How common and devastating are birth defects?

Birth defects are more common than many of us imagine. Severe birth defects occur in some three to six percent of live born babies. That percentage is greater in embryos that don't make it through to birth.

Globally, that's between four and eight million babies born each year with a severe birth defect. And the most common type of birth defects are heart defects representing a third of the total.

As a parent, I can only imagine the stress of having to go through this. Some birth defects are relatively simple and might only require one intervention to rectify them fully. Others, for example, the worst type of heart defect, require three open heart surgeries before the child reaches kindergarten.

Some children also have more than just a heart defect. They have vertebral and kidney defects as well as a cleft palate, for example. For the families, it's not just one operation or intervention, it is a constant array of appointments and visits to the hospital. And that would be tricky enough if you live near a nice big teaching hospital that does this type of surgery. But for those who live in regional remote areas, that adds an extra level of complexity for them.

What do we know about the causes of birth defects?

Like all diseases, birth defects are caused by genetics, environmental factors, and then what we call gene environment interactions, so a mix of the two. We only know the cause of around 20 percent and of those, about five percent are understood to be due to environmental factors such as the mother having diabetes. Then we also know that embryos can have chromosomal abnormalities like down syndrome. And then in terms of genetics, there are a number of genes that have been identified that if one carries a mutation, then that actually causes that birth defect.

How did you set about trying to uncover some of the causes in the remaining 80 percent of cases?

We focused on the genetic causes, so we began by recruiting families who've had a child with a birth defect, and they are always very willing to be involved in research because they want to know why it happened. We isolate DNA from their blood and then start looking for the mutations. It truly is a needle in the haystack as there are 20,000 genes and six billion pieces of genetic code.

And it's not just finding the one mutation that's caused the disease because we all carry about two million mutations or variations in our DNA. At the Institute, we have computational biologists who help us with this problem. They take all the genetic material and start sifting through it and apply filters, so we end up with a short list of perhaps 10 genes that look like they have the most damaging mutations in them, and also that they’re very rare in the general population too. From this short list, we can then start finding extra evidence to decide which of those was the mutation that caused the defect in the baby. 

What made you focus on Nicotinamide adenine dinucleotide or NAD?

NAD is a vital molecule that is required in every single cell in our bodies. It has hundreds of roles within our bodies including being an energy producer.

In 2017 we published our NAD and birth defects discovery in the New England Journal of Medicine. We had identified mutations in babies that had heart, vertebral and kidney defects and cleft palates, and they had mutations that prevented NAD from being generated and so the patients had very reduced levels of NAD. Interestingly, these families also experienced recurrent miscarriages that we felt might also be caused by NAD deficiency.

These mutations are involved in generating NAD from tryptophan. Tryptophan is an amino acid that we must eat in our diet. And these mutations blocked that pathway. And so that's why there was not enough NAD present when those embryos were developing.

There was evidence in the babies that they had NAD levels, but we were lacking the evidence that proved that those mutations in low NAD levels actually disrupted their hearts, vertebrae, and kidneys during development.

How did you prove the theory that low levels of NAD caused birth defects?

What we do in my lab is use mice as a model for human embryonic development. You might be surprised to learn they have the same 20,000 genes as humans. Mice are a wonderful model for understanding human embryogenesis. We took the mutations that we identified in these families that had low NAD levels in the children, and we made those mutations in mice. And we asked the question, are the mouse embryos normal or did they develop the same types of defects in the humans, and they developed the same defects as the human. We then continued with the mice and showed they too were NAD deficient. 

As well as finding a cause, you then went out to potentially find a solution?

Yes - the next step was to understand the mechanisms. We knew the mice were NAD deficient because the mutation was blocking them making NAD from tryptophan. I wanted to see if there was a way around this block. And we found another way of boosting NAD levels by adding vitamin B3. So, we gave the mother mouse vitamin B3 in her drinking water while she was pregnant. Every one of the mouse embryos that had carried these detrimental mutations were all alive and completely normal as a result. That also proved that it was the NAD deficiency that was the problem. It was a stunning result and the culmination of 12 years of work.

What were the implications for humans?

At that stage all we had really shown was that rare genetic mutations had caused some birth defects and miscarriages. I started to think about this on a population-wide level rather than just rare genetic mutations. So we went back to the mouse model, but this time we took mice that had no mutations and lowered their NAD levels. They went onto have the same heart vertebral kidney defects. When we popped vitamin B3 in the drinking water, all that went away.

So being able to just manipulate the levels of NAD with diet alone made us realise that deficiency in NAD on a normal population level could be a cause of miscarriages and birth defects.

What were the next steps?

We had to find out more about the role NAD and the tryptophan-vitamin B3 pathway played in pregnancy. We did know that there were some things that can affect a person’s NAD levels, such as having a high BMI, having diabetes or not being able to absorb your foods and nutrients properly due to irritable bowel syndrome or other inflammatory bowel diseases. There are several factors that can reduce your levels of NAD. Even just being pregnant can do so, which is not so surprising given you are providing nutrients and energy for another individual from your own body.

But no one had ever measured NAD levels or vitamin B3 levels in women and pregnant women before. We had to go out and set the standards. We started a study at the Royal Hospital for Women at Randwick, and we recruited non-pregnant women, pregnant women with a normal pregnancy, women who are having recurrent miscarriages, women with diabetes and women who are carrying a child with foetal anomaly. The first two groups, the non-pregnant and the healthy pregnant are our control groups and they're allowing us to set the level of what's the median level of NAD in these women and what's the range.

The point of the study is to determine if women with adverse pregnancy outcomes have lowered levels of NAD, and to identify what's a low level and then work out how much women need to take to get the NAD levels back up to what would be a normal range. We just finished that study and are now analysing the results. This is the first study of its kind, and we've funded it entirely from philanthropic funds.

Is the hope this clinical study and subsequent trials could lead to women being recommended the right level of supplementation of B3 to prevent birth defects?

It's important for us to understand when women should be taking higher levels of vitamin B3 – a vitamin that is already included in pregnancy multivitamins but at very low levels. Some might say it's not necessary to do all these steps and all this research because B vitamins are water soluble which means you excrete any excess so there’s no problem with taking high levels of B3. It’s hard to argue against that, however we don't know if a very high amount of B3 might be detrimental during pregnancy. So, we’ve started doing experiments in mice to see if that does happen. It is important that if we change clinical practice or advice to the general population, that we have good solid evidence that it is not going to cause harm.

How do you feel about your achievements thus far that could help prevent some cases of birth defects?

The beauty of our discovery is that we're talking about a cheap, simple water-soluble vitamin that could prevent cases of miscarriage and birth defects around the world and especially so in more remote areas where women lack access to high level pregnancy care.

I do want to emphasise though that we are not suggesting reduced NAD is the cause of most birth defects or miscarriages, but it's a contributor. And how much of a contributor, one day we may know. 

I am extremely grateful to the wonderful team of researchers and clinicians who have contributed to this discovery and our ongoing studies. And of course, none of this would have been possible without the support of the Victor Chang Cardiac Research Institute, which is the most inspiring place to work and discover. We are also extremely grateful to those who have provided funds for this research.

This interview has been edited from a Hearts & Minds podcast. A huge thanks to host Maggie O’Neill and interviewer Paul Rayson.