6 December 1996

No genetic susceptibility to BSE – studies reveal

By Liz Mason

NO EVIDENCE has yet been found to support suggestions that differences in genetic susceptibility to BSE exist among UK cattle.

Prof Robert Curnow, of Reading University, told a special meeting on BSE and CJD organised by the medical section of the Royal Statistical Society, that MAFF-funded research has not found any evidence of inheritance of susceptibility to BSE.

The work, started in 1990 by Prof Curnow and a colleague, was sparked by the low incidence of the disease within herds, with most having only a couple of BSE cases. One explanation could have been that some cattle were genetically susceptible to the disease.

But the studies have not provided any evidence that there is inherited susceptibility, said Prof Curnow. And he added that he did not believe that large numbers of resistant cattle existed as most were susceptible to infection.

"When we started this work we expected to be overtaken by molecular geneticists. I am a bit surprised that six years on that hasnt happened," he said.

"That seems to me to add to the evidence that perhaps genes are not involved."

But senior MAFF officials have suggested differences in genetic susceptibility to contaminated feed may account for risk differences found in a MAFF trial between calves of BSE cases and calves whose dams have not had BSE.

MAFF scientist John Wilesmith, who heads the research team responsible for analysing the trial, told the conference that all the animals involved in the trial had now been slaughtered. But not all of them had been examined.

The interim results, released in August, suggested that the risk of maternal transmission was about 10% for the BSE infected cows.

But further analysis found a variation in the risk for animals born in different years. For those born from July 1988-Dec 1988 it was 7.8% and for those born in 1989 it was just 3.5%.

"There may well be some sort of maternal effect that may be due to a true maternal transmission but it may be due to an underlying genetic predisposition," he added.

He told FW that the scientists would do their best to disentangle the two factors. But there were no promises that they would be able to provide a definite answer.

"The case control study may enable use to separate the two but we cant tell as yet," he added.

&#8226 All 14 confirmed cases of new variant CJD have a specific genetic variation in common, Prof James Ironside of the CJD surveillance unit, Edinburgh, told the conference. And five cases have a family history of dementia.n