Mary McGuire feels lucky to be alive. The 22-year-old media graduate from Limerick was just 12 years old when her eldest sister, Martina, died suddenly and inexplicably in her sleep.
But what Mary didn't know then was that she was suffering from the same rare genetic heart condition that had claimed her sister's life.
It was only when her first cousin Sarah (26) went into cardiac arrest in Australia nine years after Martina's death that Mary and other family members were tested and found to have Long QT Syndrome, an abnormality in the heart's electrical system, that had most likely claimed Martina's life.
Martina was 17 when she passed away in her sleep four days before she was due to collect her Leaving Certificate results.
"I remember Martina's death very well. We had been at the Dublin Horse Show on the Wednesday, Thursday and Friday. We got home on the Friday night at around 10pm. Martina had a part-time job in the Crescent Shopping Centre and was working on the Saturday morning.
"My Mam woke around 8am and went to wake her for work. She thought she was after sleeping in. We were all actually after sleeping in. She found her dead in her bed.
"The ambulance came and took her off but it was too late," she recalls.
The tragedy devastated the family. Martina, the eldest of three girls, had dreamed of becoming a primary-school teacher and her exam results four days later revealed that she had earned a place at Mary Immaculate College.
"It was a complete and utter shock to all of us. She was my big sister. She was the one I looked up to. I was quite babyish as a child and she was the one who always minded me.
"She was very kind and caring," says Mary. Most shocking of all was that Martina had shown no signs of being ill in the lead-up to her death.
"There were no outward clues to her being unwell – none at all. She had been looking forward to her Leaving results and to starting college," says Mary.
Even after the post-mortem the family remained in the dark as to what had been the cause of Martina's death.
Blissfully unaware that she too had inherited the syndrome, Mary took part in a skydive when she was 16 years old.
But everything changed in 2011 when Mary's first cousin Sarah McGuire (26) went into sudden cardiac arrest in Australia.
She was clinically dead for six minutes, but thanks to the efforts of her boyfriend and a member of the hotel staff she was revived.
An anxious Mary awaited news in the United States.
"It was awful. I was frightened because I didn't know what was going on and naturally my parents were trying to protect me a little," she recalls.