Chelmsford Prison officers and ancillary staff have volunteered to become potential bone marrow donors in a race against time to save the life of a five-year old boy.

Harry Cass (pictured right) was diagnosed by doctors at London's Great Ormond Street Hospital in July as suffering from the early stages of Adrenoleukodystrophy (ALD).

More than 100 prison workers agreed to be screened after hearing of Harry's plight from his father, Simon, 28, who became a prison officer four years ago after active service in the Gulf War with the Royal Military Police.

Simon and his wife, Emma, 26, of Moulsham Lodge, Chelmsford -- who also have a daughter, Philippa, three -- are hoping that other UK prisons will follow Chelmsford's example.

"Harry looks like any other lively little boy, but a transplant is his only hope," said Simon.

"The chances of arresting ALD, which is a genetic disease that attacks the brian, is greatly increased if it is diagnosed early, as it was in his case."

Earlier this week, Harry began a course of Lorenzo's Oil, the costly controversial "miracle cure" invented by American parents whose remarkable fight to save their son was the subject of an acclaimed film.

Blood tests will be carried out at the Springfield Road jail next week by the Anthony Nolan Bone Marrow Trust as a global search continues to find a perfect tissue type match for Harry.

Emma, a nurse at St John's Hospital, Chelmsford, said: "We are so very grateful to those at the prison who can take part. Who knows? Someone there could save our only son's life."

Potential donors can contact the Anthony Nolan Trust direct on 0990 111533. Donors must be aged between 18 and 40, be in good health, weigh more than eight stones and be willing to donate marrow to any patient if matched.

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