Little Billy Broxup hopes his brave big sister Amy-Jo can save his life.

Four-year-old Billy, pictured with his sister, has acute myeloid leukaemia and his best chance of survival lies with his sister donating her bone marrow for a transplant.

The eight-year-old has undergone tests to see if she is a match for her brother and the family is waiting for the results which could save Billy's life.

Claire Broxup, mum of Amy-Jo, Billy and two-year-old Lucy, said: "Amy-Jo is his only hope because there is such a shortage of donors.

"She has been so brave. I have explained to her that her blood is good and it is to help Billy. She is quite pleased that now she can actually do something to help. She understands how poorly he is."

Claire, 26 and her partner James Farndale, 22, of Blackshaw Drive, Buttershaw, were devastated when Billy was diagnosed with the life-threatening disease in September last year.

They watched Billy go from a bright and lively boy to a shadow of his former self.

"He lost so much weight it was like having a baby again," said Claire. "A mother should not have to see her little boy go through that. I just felt helpless. It was like watching him disintegrating in front of me."

Billy underwent six months of intensive chemotherapy at St James's Hospital in Leeds. He lost all his hair and at one stage was admitted to intensive care he was so poorly.

In February his treatment was complete and Billy was able to come home, with the illness in remission. But he never recovered as well as expected.

"He has not been able to go to school at all," said Claire. "His legs are an ongoing problem as his bones have been eaten away."

Then the family was dealt a bombshell when doctors said the leukaemia had returned.

Amy-Jo was immediately tested to see if she could provide her brother with a bone marrow transplant but before that Billy faces a further course of chemotherapy and also radiotherapy to be well enough for a transplant to be carried out.

"We are trying to keep positive but we just think, why us? We have been through it once, everything is so much more difficult this time around," said Claire.

Before Billy starts his second round of treatment the family went on holiday to Primrose Valley, organised by the charity Candlelighters.

"This holiday was so important," said Claire. "The illness has split the family in half. Amy-Jo has been too upset to visit her brother in hospital. I stayed with Billy during the week and missed the girls, and James stayed at the weekend.

"This was our first chance to go on holiday as a family. It had crossed my mind he could get ill but the hospital trusted my judgement and knew that I would not put him at risk.

"He was on painkillers which keep him going."

Now Billy is due to go back to hospital to start his chemotherapy and the results from Amy-Jo's blood test will be waiting.

"We are keeping our fingers crossed but if Amy-Jo isn't a match we will do our very best to get one that is," said Claire.

Consultant paediatric haematologist, Dr Mike Richards, of St James's Hospital, who is treating Billy, said there was a one in four chance of his sister being a match.

If she is not a match he said there was a possibility of never finding a donor. "It depends on how rare his tissue type is," he said. "If it is rare it can take a long time to find a donor and there is a chance of never finding one at all."