A genetic mutation has been found in a quarter of unexplained sudden death cases studied in world-first research of New Zealanders and Australians.
The findings have prompted calls for further testing and study.
Researchers from the University of Sydney uncovered the relevant genetic mutation in 27 percent of unexplained cases where young people died suddenly.
The study found that of the 490 people from Australia and New Zealand aged 35 or less who had died, 40 percent of cases were unexplained at autopsy.
Lead researcher Chris Semsarian further screened 91 unexplained cases, which revealed the genetic link.
"This sort of finding has major implications for initiating prevention strategies within the families and also at a greater community level," he said.
"The family is at risk of the same condition and, in fact, they have 50 per cent chance of having the same condition."
Kathy Curtis' son Ben died suddenly in his sleep aged 30, with a post-mortem examination finding no explanation.
Fifteen months after he passed away Ben's parents discovered he had Long QT Syndrome, a heritable heart condition which can cause irregular rhythms.
He was found to have the genetic mutation passed on by his mother, leading the family to call for further testing to prevent deaths in future.
"It's incredibly important to let people know that the slightest, little symptom needs to be checked, because from my perspective, losing your child to something like this is the hardest thing I have, I can imagine anybody, having to go through," she said.
"Seeing I was the one that gave it to him, I found it quite confronting and questioned my ability as his mother," Ms Curtis said.
"It's still that way... It's still very hard."
Since her son's death, other members of the family were found to carry the genetic trait.
Professor Semsarian said uncovering the prevalence of a genetic mutation was saving lives.
"There are many things we can do to prevent sudden death, but we need to know that the person's at risk and that's the main issue."
He said those who carried the genetic mutation could take medication or have a defibrillator implanted.