Should genetic screening tell us that we're going to be ill?

The Supreme Court's recent decision to allow parents to stop their newborn children from being tested for phenylketonuria, or PKU, has put the spotlight on medical genetic-screening programmes.

Screening for PKU and other conditions can contribute to personal and public health, as Dr David McConnell, who is professor of medical genetics at Trinity College, Dublin, said at a conference last week.

He called for more genetic-screening initiatives, but warned that we need to tease out their social, political and legal bases.

Iceland is a good example. Its government is setting up a family and health database, to cover the entire population.

The genetic information it contains will reveal much about people's predisposition to heart disease and cancer, as well as to more gene-specific illnesses.

Unsurprisingly, the initiative is controversial. Other countries will be watching to see if Icelanders can keep the database confidential, and whether the information on it is used for discrimination.

Farther down the line, the programme's social benefits will have to be assessed - will screening have made people healthier, for example?

We tend to think of genetic disease in terms of childhood illnesses such as PKU. But the current wave of research will have as much impact on adults as on children.

A woman may discover she has the BRCA1 gene, which means she has a very high chance of developing breast cancer at a relatively young age. Some women in this position have opted for double mastectomies, in order to forestall the disease.

Genetic screening can even influence our suitability for a particular job. Dr Robert Goldberg, a former president of the American College of Occupational and Environmental Medicine, was in Dublin recently to address the Royal College of Physicians of Ireland.

Speaking about the impact of genomics - the study of genes - on occupational health, he listed a number of areas where genetic links to workplace disease have already been discovered.

Asbestos workers with the GSTM1 gene have a much higher chance of developing mesothelioma, a rare form of lung cancer; those who work with isocyanates - volatile liquids used in the electronics industry - and have an HLA genotype are more likely to develop occupational asthma.

Liver cancer is normally quite rare. If you work with vinyl chloride and have the P53 gene, however, your chances of developing a liver tumour are much higher. Researchers believe the combination of the gene and exposure start carcinogenesis.

The real challenge for society is that you can now test for genetic risk. So what do you do with those who test positive? Do you stop them working in that industry? Or do you introduce a lower vinyl-chloride exposure level for workers with the gene?

If the test is done as part of workplace-health promotion, who owns the genetic information? Is it the worker or the company? Can it be disclosed to an insurance company?

Doctors and personnel managers have to consider the choice-versus-mandate dilemma. In other words, do you ask vinyl-chloride workers to be tested or do you make them be tested?

There is a strong argument to keep all genetic information private. If we knew we were at risk of a disease, most of us would take preventive measures, to protect our health.

Were the information to become public, insurance companies might penalise us based on our genetic predisposition to illness, which would probably make most of us extremely reluctant to be screened, despite its preventive value.

The scientific discoveries will continue apace. The question for us to consider is whether we can deal with the legal, ethical and social implications of genetic screening for disease.

You can e-mail Dr Muiris Houston, Medical Correspondent, at mhouston@irish-times.ie or leave a message at 01-6707711 ext 8511. He regrets he cannot reply to individual medical problems