COREY Halliday looks like an ordinary 13-year-old.

But behind his cheeky grin is an extraordinary teenager, born with a one-in-a-million illness that threatens to cut him off from the world.

Corey is one of a handful of Australians diagnosed with Kostmann's Syndrome, a severe congenital disease that means his body cannot fight bacterial infection.

Paper cuts, colds and mosquito bites have all put Corey in hospital - he has been admitted about 80 times - because he does not produce the white blood cells needed to battle illness.

"Basically, Corey should be a boy in a bubble," said his mother, Amanda Halliday.

"He should not be allowed to go outside, mix with other kids or go to school..

"We can't wrap Corey up in cotton wool - and we haven't - because it would be no life for him."

Having survived life-threatening conditions including pneumonia, blood infections and a lung abscess "the size of his lung", Corey is now a sports-mad student in year 8.

But his biggest battle lies ahead.

The Ferntree Gully teen urgently needs a bone marrow transplant to prevent the imminent onset of leukemia - and potentially cure him.

Monash Medical Centre check-ups showed Corey has developed myelodysplasia, a precursor to the blood disease.

"If we don't do the transplant, he's going to get leukemia," Dr Peter Downie, from the Royal Children's Hospital, said.

"We've got to do it within the next three or four months. To leave it any longer is risky."

However the risks of going ahead with a bone marrow transplant - a procedure similar to a blood transfusion - are equal to doing nothing.

"There is a risk Corey may die from the transplant . . . but if the bone marrow takes, Corey will be cured," Dr Downie said.

Three potential donors have been found and the transplant could be done within weeks. If successful, Corey will miss school for at least six months because of his risk of infection.

Brave Corey, having always beaten the odds, is looking to the future.

"After (the transplant) I won't have to worry about the little cuts all the time. Things will be normal," Corey said.