The recent petition calling for Kathleen Folbigg’s release hinges on cutting edge science that has identified a small protein mutation. How can something so miniscule have such a fatal effect, and what is the role of mutation in the Folbigg case?
Genes hold code for proteins, which are the components of our body chemistry that actually do things. Enzymes, hormones and antibodies are all types of proteins.
They are made of chains of amino acids, which join together like a string and fold into a 3D shape that can perform a function.
Ultimately, when a protein is not functioning correctly, or cannot function at all, it is because one or more of the amino acids was incorrect.
A gene is made of small units called nucleotides that exist as DNA chains and are stored on chromosomes. An individual receives one chromosome from each parent, which means that a single gene is actually made of two smaller units called alleles. Sometimes these alleles look exactly the same (called homozygous) and sometimes they are slightly different (called heterozygous).
When it is time for a gene to be used, other molecules find the gene and transcribe it into RNA. If the DNA is the blueprint, the RNA made from this is like copying the instructions from a PDF to an email – it’s a concise format change that makes it simple to read.
The next step is to translate the RNA into a functional protein. This requires the RNA instructions to tell machines in the cell to build a chain of amino acids. The nucleotides are read in sets of three, which make a small “word” to instruct which of the 20 types of amino acid to make. Each amino acid molecule has its own unique properties and purpose.
For example, if the PDF instructions were telling you how to build a lego tower, the email might say RED, BLUE, RED, YELLOW, so you would know which bricks to use in what order.
Conveniently, that means anyone who reads the PDF will know what to expect from the tower, and anyone who sees the tower knows what the instructions in the PDF document were. If something is wrong in the instructions, there will be something wrong in the tower, and vice versa.
This is the same with DNA and proteins. When a gene mutates, the protein will often show the effect of it, because the function or shape will change. In a heterozygous individual with two different alleles, this means that both a normal copy of the protein and a mutant copy of the protein will be made.
Multiple types of mutations can happen to the genetic code; deletion, insertion and substitutions are very common. Sometimes they involve many nucleotides in the code, but sometimes a single change is all it takes to make a gene function so poorly that it causes disease.
One of the seemingly tiny changes is called a point mutation. This is when one single nucleotide is substituted with another. Often, a single nucleotide change will mean that the wrong amino acid is used in the protein, which is called a missense mutation. Sometimes this is meaningless, and other times it is devastating.
Calmodulin identified in two of the Folbigg children
Calmodulin is a protein that has many functions around the body, but the most important is to transport calcium around cells to convey cellular signals. This affects many different types of proteins and cellular processes. It helps muscle contraction, metabolism and even memory, so it’s an important protein.
The protein is made by three genes that exist as a family: CALM1, CALM2 and CALM3. All make identical proteins, but the three genes working together create a quantity of calmodulin that is sufficient to carry out the calcium transport.
As Paul Biegler explains, calmodulin is so important that tiny mutations in the genetic code can have severe effects in the protein, both at the level of a cell and that of a person’s health and heart.
Kathleen Folbigg’s court case was in 2003, when research about calmodulin was a decade away. The first calmodulin mutations found to cause cardiac arrest were first discovered in 2012, where a whole Swedish family who had a history of such disease shared the N53I mutation in CALM1, which was inherited through a dominant allele that had a high chance of causing disease.
In a 2013 report, two unrelated infants who experienced multiple cardiac arrests, as well as epilepsy and delayed neurodevelopment, had a mutation in either CALM1 or CALM2 that changed only a single amino acid.
Likewise, in a 2016 study of two genetically unrelated children who experienced cardiac arrest, both had the CALM2 mutation N98S, where the asparagine (N) amino acid at position 98 changed to a serine (S). This was very similar to a CALM1 mutation, N97S, in a patient from Iraq that also had a disease related to cardiac arrest.
Another mutation in CALM3 may have resulted in the deaths of two siblings at ages 5 and 4, as reported in 2019. That mutation – G114W – was the result of a nucleotide substitution that turned a glycine (G) amino acid at position 114 in the amino acid chain into a tryptophan (W) amino acid.
This change meant that the small glycine in that position was turned into a bulky amino acid that repels water, thus altering the properties of calmodulin, too. This prevents the calcium from binding with the calmodulin properly, so the protein can’t perform its normal function.
Another similar mutation in CALM2 called G114R, involved a substitution of a nucleotide, which altered the genetic code to carry information to make the amino acid at position 114 (the same gene position as the previous mutation) arginine (R) instead of glycine (G).
This may seem small, but a glycine is an amino acid that holds no electrical charge and an arginine is positively charged, so the two have different properties. Overall, the mutant protein had less strength to bind to calcium and a lower ability to regulate the calcium channels it is normally involved in.
From such simple mutations, many processes that rely on the calmodulin are also disrupted, and there is a chain of poorly working cellular machinery. As the 2020 research paper showed, this could have led to cardiac arrest in Sarah and Laura Folbigg (also known as Child 3 and 4).
On a larger scale, calmodulin mutations are not uncommon, and lead to disease and health issues called calmodulinopathies; these have symptoms such as cardiac arrest or heart rhythm problems (arrythmia), and, sometimes, infant and childhood death.
Ultimately, calmodulin is a protein that is very sensitive to small mutations, which can have grave consequences.
The two other Folbigg children – Caleb and Patrick (Child 1 and 2) carried variants in the BSN gene.
A 2003 study looked at the effect of a mutant bassoon protein, where part of the middle of the protein was missing. This meant that the gene, BSN, experienced a deletion mutation and some nucleotides were cut out. In turn, the amino acid chain that made the protein was missing a few amino acids and the whole protein was smaller.
Much like cutting words out of a sentence but still putting it in the book, the protein is therefore missing some important components and is unlikely to work properly.
The study found that mice who had this mutant version had recurring epileptic seizures, and 50% of mice with only mutant versions of the protein died before 6 months of age. Mice with normal versions of the protein, or both normal and mutant versions, did not experience these effects.
Another 2018 study found that in a family of people who developed symptoms similar to palsy, all the individuals affected had mutation in the BSN gene. Unlike mice, individuals with both normal and mutant versions of bassoon were affected.
They then identified that bassoon mutations were present in other people affected by a similar palsy, even though they were not related to the original family. These mutations had not been in gene databases, as there has been little data on the subject previously.
When the researchers tested how bassoon functioned, they found that normal bassoon prevented accumulation of a protein called tau, which is a protein linked to Alzheimer’s. The mutant bassoon was unable to regulate these levels in the same way.
The 2020 study found that the two male Folbigg children had a mutant version of BSN, and that Patrick (Child 2) also suffered severe epilepsy and blindness. Further investigation would be needed to establish a link between this mutation and the symptoms, because there are few studies on the clinical effects of BSN mutations to date.
Dr Deborah Devis is a science journalist at The Royal Institution of Australia.
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