Fears that the human version of mad cow disease could cause further waves of infection have been heightened by the first case in a person who is genetically distinct from previous patients.

All the 167 cases and 164 deaths in Britain caused by new variant Creutzfeld-Jakob disease (vCJD) have so far occurred in people with a particular genetic profile carried by 42 per cent of the population.

However, a young man with a different genetic type has recently been clinically diagnosed with the incurable brain condition, BBC’s Newsnight programme reported last night.

Though the patient’s diagnosis has yet to be confirmed by biopsy, the most certain method, his case offers the strongest evidence yet that at least 90 per cent of the population is susceptible to infection with vCJD through eating beef infected with rogue prion proteins.

This suggests that a second wave of between 50 and 350 further infections might be expected, scientists said.

Professor Chris Higgins, chairman of the Spongiform Encephalopathy Advisory Committee, confirmed last night that the man is thought to have vCJD.

“The individual has been diagnosed on a clinical basis only and also because of the individual’s age it does look more likely to be variant CJD than another form of prion disease,” he told Newsnight.

The case is important because predictions for the eventual size of the vCJD epidemic caused by exposure to infected beef in the 1980s and early 1990s are dependent on how the disease affects people with three different genetic profiles.

This is because the prion protein that malfunctions to cause the disease comes in three versions. About 42 per cent of the population has a version with two copies of the amino acid methionine at a key position, and all the vCJD cases recorded so far have this MM profile.

Another 47 per cent of the population has one copy of methionine and one of a different amino acid, valine, and are classed as MV. The remainder have two copies of valine, VV.

It is widely thought that people with an MM genetic type are most vulnerable and have the shortest incubation time.

It was unknown whether MV and VV people are vulnerable at all, although the scientific consensus is that the MV group is at least susceptible with longer incubation times.

The new case has been found in person with the MV genotype, suggesting that these people can indeed contract vCJD. The case has been accepted as vCJD by the vCJD Trust, though a confirmed diagnosis remains important before the implications can be judged in full.

Professor Higgins said that if the diagnosis is confirmed by biopsy, it would suggest that a second wave of infections and deaths is likely.

“Given that 160-170 MM individuals were infected we would estimate that the number of MV victims would be a maximum of 300 to 350 probably between 50 and 350,” he said.

Research with mice has previously suggested that both MV and VV people may be susceptible to vCJD, but with incubation periods so long that most carriers will die of another cause before developing the brain disease.

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