Adam Cassidy was baptised in hospital shortly after he was born with the condition.
And his mum Deirdre feared he did not have long to live.
Adam was flown from Altnagelvin hospital to Birmingham for treatment, where he was diagnosed with alpha-1 antitrypsin deficiency.
He survived, but faced complications last July and was flown to Birmingham for a liver transplant.
A year on, the 12-year-old is returning to the city as a contestant in the British Transplant Games.
Adam will take part in a swimming contest after his consultant put him forward.
The event, which started on Thursday, is due to be the largest ever with more than 1,000 transplant athletes taking part.
“It’s really exciting,” said Adam, who has been taking swimming lessons ahead of the event.
“It means a lot to me and maybe I’ll get a medal.
“Being sick was scary,” he said.
His mother, Deirdre, said the illness hit the family hard, as although it was a genetic disease, none of Adam’s relatives had ever shown symptoms.
“Adam was a healthy baby when he was born but he was still jaundiced six weeks on,” Deirdre told BBC Radio Foyle.
“Loads of tests were carried out and then they came to tell us we had to go and see a specialist in Birmingham.
“We had to get him baptised in Altnagelvin before we left…. He was later diagnosed.
“It was all very tough for us. It was new to us too and we had to learn a lot.
“Our lives changed so much from then.”
Deirdre was happy to donate part of her liver to Adam last year, but a donor became available first.“That moment was amazing,” Deirdre said.
“I’m sure Adam remembers that morning too. It was very emotional.
“As a family we know now the importance of organ donation.”
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