Feature

Shop-soiled pairs of genes

The use of new techniques in genetics is expanding. Jane Jefferson looks at what impact genetic screening could have on occupational health

Each of us has a unique set of genes. If the coded sequence is faulty or absent this can cause a genetic disease. Genes come in pairs, one copy from each parent.

While some genetic diseases require only one copy of the disease gene for the person to be a sufferer, e.g., Huntingdon’s disease, most genetic diseases are ‘recessive’, requiring both copies to be faulty before any harmful effects are felt, as in sickle cell anaemia. In these cases someone with one copy of the ‘normal’ gene is called a carrier — but they do not have the disease, but may pass on the ‘faulty’ gene to their offspring, as in sickle cell trait.

As the known single-gene diseases are found, interest in the genetic background of other conditions is growing, focusing on our individual differences. Out of any two people who smoke the same number of cigarettes per day, why might one get lung cancer and the other never cough?

Of course they may have different health histories, exercise regimes and diets, but some of the difference is held to be the result of their different genetic makeup. They have different genetic ‘susceptibilities’ or predispositions to disease.

One area that illustrates the practical and explanatory potential of the new genetics is occupational health. Some illnesses are known to be linked to exposure to toxic substances or harmful conditions found in the workplace.

The first such occupational disease, identified in 1775, was scrotal cancer of chimney sweeps linked to contact with soot.

How can we reduce occupational morbidity?

We could reduce exposure to the toxic substance through increased hygiene, protective clothing, limiting time of exposure, lowering quantities involved or substituting a less-harmful chemical or process.

In the 1970s a number of screenable genetic conditions (including sickle cell anaemia and sickle cell trait) were identified by occupational health experts as predisposing to certain occupational diseases.

They suggested screening workers for these genetic conditions, and removing from the toxic environment these ‘ hypersusceptable’ people at great risk of developing the illness. The screening could be used to move existing workers around into individually safer jobs. Alternatively, the person would be screened pre-employment and offered a job in an environment away from the harmful toxin if found to have the genetic predisposition.

This sounds like a helpful, cheap way to reduce occupational morbidity. However, there are a few problems.... The research showing links between identify genetic conditions and occupational illness, e.g., pulmonary emphysema in coke-oven workers, is often not statistically significant or conclusive. Researchers have argued for testing even when their own results were negative, on the basis of a commitment to the idea of genetic susceptibility.

A person identified by pre-employment screening as hypersusceptible will probably not be offered employment at all in an industry, rather than be offered a ‘safe’ job. People who are not identified as susceptible may still contract the disease in question. What comeback will they have against an employer?

It may be useful for individuals to know that contact with certain substances may make then ‘disabled’, but what does this information do to someone’s self-image, will it be confidential, and how will it affect their job prospects in other fields?

Although genetic screening at work is not being done much at present (a survey of the top 500 US companies showed that only 17 had tried it, and most of them had stopped) it is ripe for renewed interest — the costs of screening are falling significantly with increasing availability of gene probes and more rapid sampling.

In Britain it has not been done at all yet, but the creation of the concept of differing susceptibilities serves to distract attention from workplace conditions and focuses on occupational health worries around individuals. There are very limited resources for research into occupational illness. The new technologies could be used to assess damage done to workers’ genes through exposure to workplace chemicals. Companies seem less keen to develop this genetic ‘monitoring’ arguing that no-one knows what such DNA and chromosomal damage indicates. Recent cuts in size of the Health and Safety Executive mean that monitoring of workplace conditions is sketchy and enforcement difficult.

Successful prosecutions lead to paltry fines for companies breaching regulations.

Genetic screening at work could be cheaper than cleaning up the workplace, and focuses the cause of disease neatly on the workers. Is this way to achieve occupational health? The issue of genetic screening in criminal pathology and maternity care will be looked at in subsequent articles.