When ignorance is bliss

Most people at risk of genetic illness are refusing to have DNA tests. Tom Wilkie examines the facts that are confounding scientists

For the past decade and a half, scientists around the world have been combing through human DNA looking for the causes of inherited diseases such as cystic fibrosis and Huntington's disease. The idea was that people at risk of such conditions would want to take a genetic test.

But the researchers' expectations have been confounded. People are queuing up not to be tested. Last week, at a meeting in Cambridge, held in a room adjacent to the one where in 1953 James Watson and Francis Crick discovered the DNA double helix, the realisation gradually dawned that delivering genetic medicine to patients in the hospital clinics may prove a more difficult task than Watson and Crick's original discovery.

One mark of the doubt creeping in was last week's publication of a book detailing the first serious studies of how ordinary people react when confronted with the news that their family may have a genetic condition. The book's title is suggestive: The Troubled Helix - a deliberate play on the title of James Watson's account of the original discovery, The Double Helix.

One triumph of genetics was the isolation and identification in 1993 of the precise genetic damage responsible for causing the degenerative brain condition Huntington's disease. This is incurable, invariably fatal and afflicts about one in 5,000 people in Britain. The children of someone with Huntington's have a 50:50 chance of getting the disease. But because it only "kicks in" comparatively late - around 40 or later - someone at risk has no means of knowing for sure. If they do develop the disease they may by then have had children themselves. Their children in turn will have a 50:50 risk of disease.

When the gene was discovered in 1993, Dr Jo Green of the university's Centre for Family Research told last week's meeting, genetics researchers assumed there would be a high demand for the test developed shortly afterwards. "But only a minority of those at risk came forward for testing, around 10 per cent," Dr Green said. Although the condition is inherited equally by both sexes, more women than men came forward for testing.

Dr Green warned that even those who get a favourable result from the genetic test have difficulties coming to terms with it. There can be "survivor guilt" and a loss of identity with the rest of the family. They find it difficult to tell other family members of their result, especially siblings, because they think "if it's not me, it must be my brother or sister," Dr Green said.

Prenatal testing for Huntington's is even more fraught. If the foetus proves to be carrying the gene, then it means that the at-risk parent also certainly carries the gene and will get the disease. "If you decided to abort," Dr Green pointed out, "it's in effect aborting yourself - it's a statement about the value of your own life."

For most genetic conditions, however, those who are "carriers" of a mutated gene are completely healthy and problems arise only when two carriers decide to have children together; then there is a one in four chance that the children might inherit the mutated gene from each parent and suffer the disease. The most common genetic disease of northern Europeans, cystic fibrosis, happens in this way. About one in 25 of the population are perfectly healthy carriers of a mutated gene. The idea of a test would be to allow such people the option of avoiding having children with the disease.

But according to professor Theresa Marteau, of Guy's Hospital in London, although six separate trials of carrier testing have been conducted in Britain, "the results showed relatively little interest among the general population". There was a higher uptake of the test among women in antenatal clinics, but that may simply be a matter of the setting - where all manner of tests are being offered anyway and the CF test can be taken on the spot without the need to return for another appointment - rather than reflecting any real demand by the women themselves.

"The implementation of carrier testing has stalled in the UK and the US," Professor Marteau said. Among those tested, "over time, there was a loss of understanding of individuals' carrier status. More counselling at the time of testing is not the answer."

The Government's response to these problems has been confused and uncertain. In January, it announced the setting up of a small advisory committee. But its remit is so narrow that the committee is unlikely even to touch the issues discussed at Cambridge - the very issues that may determine whether genetic tests, developed with the best of intentions, help or harm those families most vulnerable to genetic disease.

`The Troubled Helix - Social and Psychological Implications of the New Human Genetics', edited by Theresa Marteau and Martin Richards, Cambridge University Press.