Girl, 15, among new CJD victims

Evidence is growing of a genetic link between people who develop the "new variant" of the fatal brain disorder Creutzfeldt-Jakob disease, which has been tentatively linked to eating BSE-infected food.

Two more cases of the "new variant" were announced at the weekend by the CJD Surveillance Unit in Edinburgh. Both victims were in their thirties. The diagnosis brings the total number of cases of the new strain in the past three years to 14, seven of whom have died.

A 15-year-old girl, who is still alive, has been confirmed as having CJD from tests on spinal fluid, using a technique developed in the US. She is not being included in the official statistics until the disease has run its course.

Though the growth in numbers this year could be the sign of the start of an epidemic, it is more likely to be an accident of timing, as the seven people developed the disease at different times, said Professor Peter Smith, an epidemiologist on the government's advisory body, Seac.

The new strain has been tentatively linked to BSE, or mad cow disease, because it differs in a number of respects from the classic form of CJD, which normally affects people over 60. The new strain has been found almost exclusively in Britain - apart from one case in France - in the past three years in people aged under 42. It is a similar sort of disease to BSE, in which the brain becomes "spongy" with holes.

Significantly, all of the 14 British victims have had the same genetic configuration on a particular point of the PrP gene, which produces a protein that is essential to the function of some brain cells in its normal form. In CJD, this protein's shape becomes distorted after it has been made in the body by "rogue" proteins known as prions. The particular PrP configuration found in the 14 "new strain" victims occurs in 38 per cent of the population. The fact that no cases of the new strain have occurred in people with different PrP configurations could mean that others are less susceptible to the disease.

Sheila Gore, of the Medical Research Council's biostatistics unit, called yesterday for the CJD unit to issue more information about the number of suspected "new-strain" cases referred to it, rather than issuing figures only for confirmed cases. "Though only a certain proportion are confirmed, we need to know what proportion that is," said Dr Gore. "Once we know that, we can work back from the number of confirmed cases at any stage to how many suspect cases there are which will be confirmed."

The Department of Health intends to publish its latest quarterly report on CJD cases later this month, covering the three months to the end of September. However, there are no plans at present to include suspected cases in those under 40.

Dr Gore said, "It would be useful if they did, because if it turned out that eventually 90 per cent of those suspected cases are confirmed as the new strain, we would have something to work with. If it was only 10 per cent, at least we would be able to decide not to take much notice."

Professor John Pattison, head of Seac, said "I think it's notable that the total number of referrals isn't higher than in 1994, when the unit had its highest number of cases of CJD. That means there's not a great backlog of cases that haven't come through."

It seems frustrating that we can't make more rapid predictions about the future - but we can't, and we have to accept that."