Folbigg Inquiry: Mutations in calmodulin were considered “incompatible with life” until a breakthrough discovery

The inquiry into the convictions of Kathleen Folbigg has heard that, until discovered in 2012, mutations to the genes that produce the important regulatory protein calmodulin were considered incompatible with life. 

Husband-and-wife professors Michael Toft Overgaard and Mette Nyegaard, from Aalborg University in Denmark, were the sole experts to present evidence to the inquiry in Sydney today. Due to their presentation of what Tom Bathurst KC, conducting the inquiry, described as “new and quite exceptional” information, they are the final witnesses in this hearing block. 

The inquiry has now adjourned until February, when the remaining experts will be called over a three-week period. 

Toft Overgaard and Nyegaard’s exceptional evidence relates to calmodulin and the way it interacts with calcium in human heart cells. 

They feel their evidence is so significant that they expect competing international labs will begin their own research into the findings.

“We hope not too many people are listening [to our evidence] because, of course, we are in science, we are in competition with other labs, so the first one to try and publish gets all the glory,” Toft Overgaard explained. 

“By doing this [presenting their findings to the inquiry], we have invited the competitors to run for the race. But for us, I think this [the inquiry] is more important.”

Calmodulin mutations were “incompatible with life” until 2012 

The evidence presented by these Danish scientists is central to the inquiry’s question as to whether Folbigg passed an exceedingly rare variant of the gene which codes for calmodulin to her two daughters, both of whom died suddenly.

Mutations of the three CALM genes which code for the calmodulin protein have been associated with several rare cardiac ‘phenotypes’ (or observed traits). These include Long QT Syndrome (LQTS), a condition that causes an abnormal heart rhythm, or arrythmia; Catecholaminergic Polymorphic Ventricular Tachycardia (CVPT), which is characterised by arrythmia during exercise; Brugada syndrome, an inherited arrhythmia associated with high risk of sudden death; and idiopathic ventricular fibrillation (IVF), which is a cover-all explanation for sudden cardiac arrest of unknown origin.

“By doing this [presenting their findings to the inquiry], we have invited the competitors to run for the race. But for us, I think this [the inquiry] is more important.”

Professor Michael Toft Overgaard

This gene family is so stable – that is, resistant to mutation – that it is “conserved” across all vertebrate species, meaning all animals with a backbone use the same genetic code to create the protein. The gene is also near-identical between humans and wheat, and has just three variations when the human gene is compared to its companion gene in parasitic round worm. 

That suggests calmodulin is an essential, almost invariable component of life. Variations of the CALM genes that make it are, according to Nyegaard, “ultra rare”.

This, explained the scientists, is why many researchers believed individuals with calmodulin variations could not survive, until they discovered the first mutations in these genes in 2012 – a decade after Folbigg was convicted. 

Since 2012, other benign and pathogenic CALM mutations have been uncovered by analysing samples submitted to large genomic databases such as gnomAD and the UK Biobank, they said. 

Nyegaard observed that on the gnomAD database, eight variations of the CALM2 gene exist across eight people. That means just one of these variants is found in one known person. 

With over 125,000 exomes (protein-coding regions of genomes) on the database, that represents fewer than 0.006% of the population presenting a CALM2 variation.

Folbigg is known to have a CALM2 variant called G114R. In this variant, a small glycine amino acid at position 114 of the gene is substituted by a large arginine amino acid. Her two daughters were also found to have the variant.

The calmodulin gene
A model of the three-dimensional structure of the calmodulin protein, binding with a calcium ion. Credit: Getty Images

Calmodulin affects calcium channels, and sodium ones too

Calmodulin plays an important role in regulating the human heartbeat. 

While specialised protein ion channels move calcium, sodium and potassium in and out of heart cells to trigger the electrical activity of the muscle that pumps your blood, calmodulin plays a ‘helpful’ role by binding to calcium and instructing these conduits to close. 

A typical calmodulin protein will sufficiently bind to calcium and trigger the closing mechanism once it reaches a certain point of ‘coverage’. But mutated forms of calmodulin are less efficient at this process.

That means more calcium than is necessary may enter heart cells by the time these cellular channels close. 

Importantly, the fresh discovery brought to the inquiry by Toft Overgaard and Nyegaard shows calmodulin plays a similar instructional role on sodium channels embedded in the cell membrane.

Learn more: The fresh discovery tabled at the Folbigg enquiry

Survivorship bias and Folbigg

The investigation of G114R on sodium was one of several tests conducted in response to critiques of the Brohus report made at the 2019 inquiry, of which Toft Overgaard was a senior author. 

Another observation at that inquiry was that Folbigg herself still lives with the mutation, and therefore provides an example of successfully living with the variant, and therefore unlikely to explain any cardiac conditions in her children. 

However earlier on Tuesday, Nyegaard suggested this analysis is an example of allowing a survivorship bias to cloud findings. 

Here, she used an example of World War II fighter jets returning from skirmishes riddled with shell-holes across their wings and tails, but not across other parts. 

Many researchers believed individuals with calmodulin variations could not survive, until they discovered the first mutations in these genes in 2012 – a decade after Folbigg was convicted. 

While it might be instinctive to reinforce places where bullet holes are visible, it’s where they do not occur that infers the parts of the craft where protection is vital: fighter planes that suffer damage here, never return.

The same goes for genetics.

Databases like gnomAD and the UK Biobank are stocked with genomes of adults who have submitted their genetic information. What they do not show is people who have been unable to take the opportunity to provide a sample: In the case of those with dangerous calmodulin mutations – which are known to present as a range of heart problems – death during infancy would remove that opportunity. 

The inference is that people like Folbigg may be the only people on record of having very rare CALM mutations, because others may not have survived with the gene long enough to be detected. 

Inquiry adjourned until February

The eleventh-hour provision of the new assay results from Toft Overgaard and Nyegaard has prompted Bathurst KC to call an early adjournment of this first hearing block. 

The inquiry will resume on 7 February 2023, when witnesses originally slated to appear this week will be called.

They include professors Carola Vinuesa, Matthew Cook and Todor Arsov, who worked with the Danish scientists on the Brohus paper; professors Jonathon Skinner (a cardiologist) and Edwin Kirk (a clinical geneticist), who critiqued that study’s findings; and Professor Peter Schwartz, who oversaw the Brohus paper with Toft Overgaard and Vinuesa, and also established the International Calmodulinopathy Registry.

Further reading:

The Royal Institution of Australia coordinated the effort to bring international science expert witnesses to Sydney to appear in person at the inquiry. They would have appeared by video link instead without this assistance.

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