Kathleen Folbigg has spent nearly 20 years in prison, convicted in 2003 of killing her four children. A new inquiry into the children’s deaths – the second in five years – is now underway after 90 scientists petitioned for Folbigg to be pardoned based on scientific evidence that wasn’t available two decades ago.
That evidence, gathered by an international team of scientists, points to a novel (new) genetic variant found in two of Folbigg’s children, Sarah and Laura, and Folbigg herself, that could explain how the girls died in their sleep of natural causes before turning two.
But as yet, it has not been enough to overturn the convictions. The first judicial inquiry wrestled with the new genetic evidence but ultimately, in 2019, affirmed Folbigg’s guilt. That decision reflected a host of tensions at play – in the way scientific evidence is considered by the courts and how scientists go about proving new and very rare genetic mutations cause disease.
Now, new evidence has been put forward at the latest inquiry by two Danish researchers in a bid to quash some of the questions raised in past hearings, chief amongst them being how a single genetic change in one gene could impair heart function and explain the two girls’ deaths, yet spare their mother.
Mutations in the body’s three CALM genes, which all make an identical protein called calmodulin, have been linked through a series of genetic studies over the past decade to a string of sudden cardiac deaths in young children. Calmodulin controls the flux of calcium ions into and out of heart muscle cells, which in turn regulates the steady pulse of heart contractions.
Trawling through DNA sequences in 2019, scientists discovered Folbigg and her two daughters carried a mutation in the CALM2 gene. If this now-faulty gene produced a defective protein that could no longer bind calcium ions like calmodulin should, then it may have caused irregular heart rhythms called arrhythmias, they reasoned.
However, despite a growing number of cases linking mutations in CALM genes with life-threatening heart conditions, the two groups of scientific experts tasked with providing advice to the court disagreed in their final reports to the 2019 inquiry over the likelihood that the rare mutation found in Folbigg’s children (called G114R) was responsible for their deaths.
How could the mother tolerate the same mutation as her daughters, when similar mutations have been known to cause lethal heart conditions in other children? And what triggered the sudden death of her two daughters, at 10 and 18 months of age?
Molecular geneticist Mette Nyegaard and her husband, protein scientist Michael Toft Overgaard, both of Aalborg University in Denmark, were part of the team who discovered the first mutation in a calmodulin gene in 2012.
They also led the lab studies that in 2020 showed the Folbigg mutation, G114R, severely impaired calmodulin’s ability to latch onto calcium ions and close two pivotal calcium ion channels in heart muscle cells. Ion channels acts as gatekeepers, funnelling ions into the cell or shutting them out.
But observing a change in the way a protein behaves in lab-cultured cells does not necessarily translate to what happens in the human body. That said, these types of studies are the tried and tested way of identifying new molecular mechanisms of disease.
As Toft Overgaard and Nyegaard outlined in their new evidence today, presenting preliminary findings of lab studies completed just last week, the G114R mutation also appears to interfere with how calmodulin interacts with another type of heart cell ion channel, the Nav1.5 sodium ion channel.
This is important, because Toft Overgaard, Nyegaard and their colleagues had concluded in their 2020 study that fatal arrhythmic events could be triggered by fever, the likes of which the two Folbigg daughters reportedly had in the days before their deaths. An infection, or fever, may have put added strain on the girls’ flitting hearts.
But such cases of fevers hastening arrhythmias have only been seen in Brugada Syndrome, a genetic disorder affecting children that increases the risk of abnormal heart rhythms and cardiac arrest. Mutations in Brugada Syndrome disrupt sodium ion channels in heart cells.
The Danish scientists have found that the Folbigg mutation causes a dramatic change in the shape of the calmodulin protein at the exact spot where it anchors onto the Nav1.5 sodium ion channel. With a bulky amino acid in place of a smaller one, the mutated calmodulin would not successfully bind Nav1.5, the researchers found.
With an explanatory slide on display, Toft Overgaard said: “So what you can see is that the G114R is uniquely positioned close to the sodium channel. … [At] the actual size of the individual atoms you can see that the G114, a glycine, is basically tucked into the interface between calmodulin and the sodium channel. So imagine taking the smallest amino acid in the world and putting one of the largest in place of that. We would predict that could interfere with the binding.”
When asked by counsel assisting the inquiry, Julia Roy, if he and Nyegaard would ordinarily be sharing a discovery like this with the world so quickly, Toft Overgaard responded: “No… by doing this of course we have invited the competitors to the run for the race. But for us, I think this [inquiry] is more important.”
But again, the findings from lab assays are just one piece of the puzzle. To decide whether a genetic variant causes disease, geneticists look at multiple lines of evidence, including whether mutation is rare, absent or common in the wider population, and if people who carry the mutation show any signs of disease. This is tricky to do when considering rare variants new to science.
Kathleen Folbigg is currently the only known carrier of the G114R variant in CALM2 in the world, but now another person with a mutation at the same position in the CALM3 gene has reportedly been identified in the UK Biobank, a large research database containing genetic and health information of more than half a million people.
Other scientists involved in the Folbigg inquiries have previously argued that this is evidence that the G114R mutation is benign – it couldn’t possibly cause lethal heart conditions if Folbigg and the second G114R carrier are alive, and have no reported symptoms of a heart condition.
Toft Overgaard and Nyegaard confirmed the second case but said that cases like these show that as more rare mutations in calmodulin genes are discovered, including carriers seemingly unaffected by heart conditions, the spectrum of known phenotypes continues to expand. The professors also pointed out that large registries like the UK Biobank hold data exclusively on people who have survived into adulthood when fatal arrhythmias linked to CALM mutations tend to strike before the age of six. This means those databases are enriched for individuals who are likely to better tolerate deleterious gene variants. To get the full picture, researchers would need to also look at infants who did not make it past childhood.
Toft Overgaard and Nyegaard also explained that mutations in CALM genes are rare precisely because they are so deleterious. Natural selection usually weeds out damaging genetic mutations, especially in critical genes. The CALM genes are so vital to heart cell function that relatively few mutations are found among them – and the ones we know of have grave consequences.
Also, not all mutations ‘penetrate’ the cacophony of molecular activity inside cells to manifest in disease. Recent research, in particular driven by sequencing of large cohorts, shows many other pathogenic variants in other genes has reduced penetrance in the population, whereby some people who harbour mutations don’t develop disease. This is likely the case for G114R too, Toft Overgaard and Nyegaard argued, and could explain why Kathleen Folbigg is still alive.
As Cosmos reported yesterday, Toft Overgaard and Nyegaard’s new material has altered the shape of the inquiry. Its head, Tom Bathurst KC, said today: “People haven’t had an opportunity to consider [Overgaard and Nyegaard’s] most recent report, which is obviously highly significant.”
Bathurst has now adjourned this first hearing block to allow the other expert witnesses to review the results of the study.
The second hearing block will commence as scheduled on 13 February 2023, but will run for three weeks, not two.
- Life with a calmodulin mutation was once thought impossible, Kathleen Folbigg is an “ultra rare” survivor
- Day 1 of the Folbigg enquiry: “Exceptionally rare” calmodulin mutation could lead to cardiac arrests
- Cosmos Q&A: The clash between law and science
- Behind the science of the Folbigg petition
- Folbigg case: timelines compared
- Infanticide vs. inherited cardiac arrhythmias