ONE in five people with a deadly inherited heart condition are only diagnosed after the loss of a loved one.
Figures from British Heart Foundation Northern Ireland also reveal one in six are diagnosed only after suffering a cardiac arrest.
BHF NI has now launched the In Your Genes campaign, so people can be identified before a tragedy.
Around 17,500 people in the north have a faulty gene, putting them at a high risk of developing heart disease or dying at a young age.
Each child of someone with an inherited heart condition has a 50 per cent chance of having the same faulty gene, but the majority remain undiagnosed.
It is estimated at least one person aged under 35 dies every month from an undiagnosed condition.
Joe Burns (23) from north Belfast, died in July 2014 after collapsing at his parents' home. The family of the popular barman, who was a fit and healthy boxer, spent months not knowing how he died.
They were referred to the inherited heart conditions clinic in Belfast for genetic testing and have since learned his mother Una and sister Jeanette both carry the faulty gene for Long QT, which can cause heart rhythm disturbances.
Ms O'Neill said: "When Joe died our family was absolutely devastated.
"It's very hard to hear that you carry the gene for a potentially deadly heart condition but thanks to the testing we now know we have this gene and can be monitored.
"Our family have dedicated ourselves to raising money for BHF since Joe’s death because we want to fund the research that will save lives."
Jayne Murray from BHF NI said more research is needed to better detect and treat heart conditions.
"All too often, people aren’t familiar with their family history, or they aren’t aware that a sudden death might be linked to an underlying heart condition," she said.
