A cardiologist has told the second inquiry into Kathleen Folbigg's convictions for killing four of her children a genetic variant identified in herself and her two daughters is exceptionally rare.
The inquiry, being conducted by former chief justice Tom Bathurst, began in Sydney on Monday.
The retired judge was appointed in May after the NSW Governor received a petition from prominent scientists asking Folbigg be pardoned due to new scientific evidence.
Her lawyers have submitted the evidence indicates a genetic mutation could be responsible for the deaths of two of the children.
Known as CALM2 G114R, the variant affects the calmodulin protein and the body's ability to bind calcium.
It has been identified in Folbigg and her daughters Sarah and Laura, and can affect the electrical activity of the heart, Monday's hearing was told.
However, very little is known about the variant, cardiac electrophysiologist Hariharan Raju told the hearing.
"Calmodulin variants are relatively recently described and are exceptionally rare conditions," Associate Professor Raju said.
"So much so, as someone with an interest in cardiogenetic disease ... (she) is the first individual that I have personally been involved with."
He conducted an electrocardiograph on Folbigg before the earlier inquiry, but aside from viewing historical results of other tests, has not consulted with her since 2019.
"To my knowledge no other cardiologist has consulted with her," Prof Raju said.
He said he had been asked by a legal team to run a specific test, "which is not the normal patient-physician relationship".
Folbigg has declined to participate in further tests ahead of the current inquiry.
"Overall, I still feel she doesn't have sufficient data to confirm a diagnosis," Prof Raju said, noting she did have some minor abnormalities.
"When I consulted with her, although the DNA variant had been identified, it wasn't clear at that point whether it was responsible for any disease at all," he said.
"I essentially kept an open mind in the context of her family history as to what might be the underlying condition that ties together all the tragic events in her family."
Counsel assisting the inquiry, Sophie Callan SC, asked what tragic events he referred to.
"The deaths of her four children," he said.
Folbigg was jailed in 2003 after being convicted of murdering her children Patrick, Laura and Sarah, and the manslaughter of her son Caleb.
Former NSW District Court chief judge Reg Blanch conducted the 2019 inquiry, concluding her guilt was "even more certain".
Folbigg previously lost challenges in the NSW Court of Criminal Appeal, the High Court and the NSW Court of Appeal.
Ms Callan has acknowledged the "unusual position" of the inquiry being held soon after the earlier inquiry based on asserted new scientific evidence.
She began on Monday summarising the deaths of the children, the subsequent trial, and the 2019 inquiry, noting the science of genetics has evolved over the years.
"There was a huge amount of progress between the trial in 2003 and the inquiry in 2019, with more progress since then," Ms Callan said.
Mr Bathurst's task is to form his own view about whether there is reasonable doubt about Folbigg's guilt.
She was initially sentenced to 40 years' imprisonment, with a non-parole period of 30 years, but an appeal later reduced her sentence to 30 years with a non-parole period of 25 years.
She's not eligible for parole until 2028.
Scientists calling for her early release argue there is no medical evidence she smothered the children she has been convicted of killing.
The hearing continues.
