The trend could also lead to difficult ethical decisions, mirroring those in which hospitals have refused to perform heart operations on smokers, with health professionals having to base decisions about who to choose for particular therapies on their genetic make-up.
"The increasing emphasis on genes and diseases is likely to lead to a lowering of motivation to alter one's lifestyle to reduce risk," said Theresa Marteau, of the psychology and genetics research group at Guy's Hospital. "But it always affects how we react to others' illnesses. It increases the sense of pity."
Unpublished research by a researcher working for Professor Marteau found that people show less sympathy to those who decline tests to see if they are at risk of developing a genetically-linked disease, but subsequently develop it.
In an experiment in which people were asked about their level of sympathy to a hypothetical mother whose baby was born with Down's syndrome, they showed less sympathy if she had refused the pre-natal tests.
In another experiment, parents were told that their babies' raised cholesterol level was due to a genetic predisposition. One said: "I feel as though a death sentence has been pronounced on my boy." But another group of parents, whose babies also had raised cholesterol but were not told it was genetic, reacted with equanimity. "It's only a dietary thing," one said.
Professor Marteau said: "In 30 years, the Human Genome Project [which aims to decode all of the human DNA code] could result in therapy and control for previously incurable diseases.
"But long before that we will be able to predict the condition. And what we see as causing the illness is an important factor in what we do about it."
Existing tests can already uncover genetic predispositions to heart disease, breast and colon cancer and diabetes. But under current practice, insurance companies and employers are not allowed to ask for a test to be carried out before offering insurance or health cover, or employment.
The results of the latest research suggested that restrictions should be imposed on the availability of screening for certain genetic conditions, Professor Marteau said.
The growing awareness of genetic predisposition to various conditions can make people less interested in trying to change their lifestyle. One study of heart-attack victims found that if they thought the disease was caused by inheritance they were only half as likely to change their lifestyle as those who believed that it was a random occurrence.
The belief that genes determine lives has taken an extraordinary hold, with one man in the US claiming he was genetically predisposed to murder. His appeal failed. But the belief in the power of genes to shape lives could help one group, Professor Marteau said. "It might change others' attitudes to those who are obese."Reuse content