Podium: A window of opportunity for genetic testing

Virginia Warren From a presentation by the consultant in public health medicine at Bupa, delivered at the Royal Society for the Arts

EVERY ONE of the millions of cells in our bodies contains a full set of the blueprint required to build and run the whole concern. They differ by which bit of the blueprint - which bit of the DNA - they have "switched on" at any given time. The DNA is organised on 46 chromosomes in the middle (the nucleus) of each cell: 23 pairs. The collective name for all the chromosomes is the genome.

This is a good opportunity to reflect on an important concept, which is that, for the population in general, there is no such thing as a clearly bad genome. Genes that brought only disadvantage would have been excluded by natural selection.

It is desperately sad for people with cystic fibrosis that present circumstances mean that they lead difficult, shortened lives, and the rest of us must remember that we have a moral duty to support and care for them, as it is common among people of European descent to have one functioning copy of the cystic fibrosis gene and one mutated, non-functional copy. These people have normal lung structure and function, and it has been suggested that the mutated version of the cystic fibrosis gene may confer some protection against serious gut infections.

So the unlucky people who get two copies of the mutated gene are paying the price for our ancestors having avoided or survived typhoid and the like in previous centuries. A similar situation may exist in relation to schizophrenia and language acquisition, that being a partially genetic disease.

A very important implication of this phenomenon is that all of us must have some superficially undesirable genes - it is just a matter of which ones. As a society we should think carefully about categorising people as relatively restricted in which jobs they can take up, or as relatively expensive to care for, because, as individuals, the knock may well come on our door when the tests for our dud genes happen to come on stream.

We have seen how having one copy of an undesirable gene can be unapparent. It may well be possible even to have two copies, with their effect being masked by other influences, and this ties in with another key concept.

This is that diseases wholly due to genetic changes are rare. The diseases that give rise to many years of symptoms for many people - things such as ischaemic heart disease (which produces angina, heart attacks or sudden death), stroke, diabetes, osteoarthritis, osteoporosis and Alzheimer's dementia - seem to be caused by mixtures of genetic and environmental or lifestyle risk factors. It appears that the environmental/lifestyle factors are as important as the genetic ones, so the potential for genetic medicine to relieve this burden of disease will be limited unless it turns out that one or more genetic factors are "compulsory".

A specific example of the sort of effect I am talking about is the type of diabetes that has its onset in childhood. Genetic susceptibility is clearly important, but exposing the young immune system to cow's milk protein and catching one or more apparently mild infections in a vulnerable period in early childhood also have roles to play. So we need to work on the permutations of genes, bugs and diet to work out a protective strategy.

That move to prevent disease could involve immunisation. One could imagine it being given to babies whom testing had shown to be genetically susceptible. This hypothetical situation, which is at least five to 10 years away, mirrors a current one. Babies born in the UK have a blood sample taken (heel prick test), which is biochemically tested for a chemical called phenylketonuria, or PKU, the levels of which are controlled by a particular gene. If it is abnormal, the child needs to live on a special diet to avoid permanent brain damage.

Society has a window of opportunity to debate whether it is desirable to seek to minimise people's right to gain access to genetic testing over the counter. It hardly happens in the UK at the moment, and it would be possible to regulate or legislate against over-the-counter sales of tests or testing services, although not to control Internet sales.

The issue about small groups with high resource requirements needs exploration, too. If long-term care is to be funded through private insurance rather than by the state or the sale of property, the industry needs to have clarified whether the excess cost of a small group requires a separate risk pool charging higher premiums.