Illness has followed Mr O’Brien-Smith his whole life, and his mother said she never felt able to let her guard down.
“It feels like the odds are stacked against you,” she said.
“I feel physically sick with worry. At times this literally feels like living hell.
“Louis has always lived on the edge of a cliff but this time it feels as if we are that bit nearer the edge.
“Looking back at that time of leukaemia and chemotherapy, it was living hell, but you switch to autopilot and children bounce back unbelievably.
“Now with the cardiac issues, things feel so much harder, because Louis isn’t a small tot who is unaware, he’s now a young adult who sometimes wishes he was never even born.”
At only 4ft 10, Mr O’Brien-Smith’s size will affect his treatment, including the need for paediatric tubes.
He also has signs of congestive heart failure, and has incredible difficulty walking as the effects of the chemotherapy have also eroded his bones.
“His X-rays show no ball-shaped sockets. Both sides have all worn away,” Mrs Speirs said.