The boys are four of only 100 people diagnosed with XLP

All four Hartley brothers, from Romsey, Hampshire, have the extremely rare XLP condition, which attacks the immune system.

After a nationwide appeal for matching donors, a person has been found to be a 90% match to eight-year-old Daniel.

The eldest boy, Joshua, 12, is already set to receive a transplant from his mother, Allison.

Worldwide search

The boys' father, David Hartley, said: "It is very significant news - the nine out of 10 match for Daniel is good enough to go to transplant.

The match is good enough for Daniel to undergo a transplant

"We would have preferred a 10 out of 10 match, but it is good news that we can go forward."

A spokeswoman from the Antony Nolan Trust, which maintains a register of bone marrow donors, said: "The response to David's campaign has been absolutely incredible.

"It shows there is such a thing as community spirit."

Donors are still being sought for the other two boys, Nathan, 10, and Luke, four.

More than 500 people have already given blood samples in the search for suitable bone marrow donors.

Anyone who is healthy and aged between 18 and 40 can join the Anthony Nolan Trust register and see if they are a match for the boys.