DNA tests lead to early discovery of Sudden Arrhythmia Death Syndrome

Before Jennifer's mother died in 2005, she would often faint early in the morning. Her family had no idea what was causing the fainting spells, but the last time it happened, the 53-year-old lapsed into a coma for six months and died.

It was while she was in a coma when doctors found the cause: she suffered from Long QT Syndrome, a rare congenital disorder of the heart's electrical system that predisposes sufferers to irregular heartbeats, fainting spells and sudden death. There's a 50/50 chance that the condition will pass from an affected parent to child, so Princess Margaret Hospital ran a DNA test on Jennifer and found that she also suffered from the condition.

"Many members of my family were DNA tested. My younger sister and I, my son, and my younger sister's twin girls have it; my mum's siblings have been spared. There's no cure for the condition, but I am taking drugs to keep it under control," says Jennifer.

"It turned out the shrill ringing of the alarm clock caused my mum's fainting spells, so I stopped using an alarm clock, and I avoid strenuous exercise, too. I have taken all the right precautions, and I am glad that I can live like an ordinary person."

Between 2008 and 2012, 289 young people aged from five to 40 died because of heart diseases. Seventy-two of the victims, or 25 per cent, were found to suffer from Sudden Arrhythmia Death Syndromes (Sads), a group of inherited cardiac rhythm disorders that can sometimes cause sudden cardiac death.

However, DNA tests conducted at specialist labs such as the one at Princess Margaret Hospital help provide early diagnoses for congenital neurological, heart and paediatric diseases, says Chloe Mak Miu, consultant pathologist at the hospital.