Doctors are to perform pioneering treatment on a man suffering from a rare brain condition that has been compared to mad cow disease.
Specialists say the "novel therapy" for Creutzfeldt-Jakob disease (CJD) has been developed over many years and will be conducted on a human for the first time following approval by a judge at the Court of Protection in London.
The fatal illness – which can result in memory loss, changes in personality, vision problems and the progressive loss of brain function and mobility – is caused by an infectious protein called prion.
CJD is described by the NHS as "similar" to bovine spongiform encephalopathy (mad cow disease), and one of its variants can affect humans who consume meat from a cow that has the condition.
Lawyers for the man given the all-clear to receive the groundbreaking treatment said he was instead suffering from the sporadic version of the disease, in which a rogue version of the protein can build up in the brain naturally.
It is the most common type of the ailment but still only affects one or two people in every million in the UK, with 90 recorded deaths in 2014.
Bosses at University College London Hospitals (UCLH) NHS Foundation Trust had asked for permission to treat the man with an antibody called PRN100, despite it having only been tested on animals.
Mr Justice Cohen was told by the trust's legal team that evidence from the trials gave "reasonable cause for hope" and had indicated that the "world first" therapy would do "what it is supposed to do".
Staff at the office of the Official Solicitor, who help people lacking the mental capacity to make decisions and had represented the man during litigation, were also in favour.
Although he was warned that there could be side-effects, the judge ruled that it was "plainly in his best interests that he should have treatment and that I should approve it".
Speaking after the hearing, trust chief executive Professor Marcel Levi described the ruling as "an important step in tackling this devastating illness".
"CJD is a rare and cruel disease which rapidly destroys the brain, affecting memory, thinking, speech, balance, movement and behaviour," he said.
"There is currently no cure or treatment for CJD. At present, caring for patients with CJD involves trying to use medicines to alleviate symptoms only."
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UCLH believe the treatment – which received significant funding from the Cure CJD Campaign – could slow or even halt the progression of the disease, although it is not expected to reverse any brain damage that has already occurred.
The patient – who the judge said could not be named in media reports – will initially receive the therapy by a drip into a vein in the arm, and will then be monitored by a team of experts from the trust.