Mary Dejevsky: Genetic testing has little value if there's no chance of a cure

If you submit to screening at, say, the age of 40, and learn that you have a predisposition to Alzheimer's, what are you supposed to do about it?

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Sometimes it is hard not to feel that the media and the medics between them have things the wrong way round. Earlier this week, a report from the Human Genetics Commission recommended that genetic testing for a range of conditions be made available to couples contemplating having children. The findings have more committees to pass through before they are acted upon, but the Commission said that there were "no specific social, ethical or legal principles" against pre-conception screening. At this point, the whole subject sank like a stone.

Go back a week, though, and another report made far bigger, far noisier waves. Scientists from the universities of Cardiff and Pennsylvania announced the identification of five gene variants that raise the risk of Alzheimer's disease. Much was made of the numbers likely to suffer from Alzheimer's (an estimated 1 million by 2021) and the cost of care (currently £23bn a year). It is not the scientists' fault, but the tenor of the reporting suggested that prevention or cure might be just around the corner.

There are some obvious reasons why these two items of news from the medical genetics front were received so differently. One is that Alzheimer's, second only to a cancer diagnosis, is the fate very many people fear, for ageing relatives and for themselves. Another is that the Alzheimer's research appeared to offer unadulterated good news: quantifiable progress towards a much-desired end – five whole new gene variants found at once. The news about pre-conception screening, on the other hand, held out no hope of cures and could be interpreted as potentially blighting a couple's hopes.

Of these two developments, however, I would argue that the possibility for couples to be screened for conditions they might pass on is by far the more significant and beneficial here and now. Discovering genetic markers for Alzheimer's is still – if you read the small print of last week's reports – at a very early stage; thus far, there is no single one that determines whether someone will develop Alzheimer's, and there may never be. It may always be a combination of different genetic variants and environmental factors.

The crucial distinction in my mind, however, is that pre-conception screening allows individuals to make an informed choice. They are tested for the propensity to pass on a condition that has already been identified – which, of course, is by no means all. They can then consider what to do about it. That might entail a decision not to have children. It might mean exploring the options for test-tube screening of embryos. It might prompt a subsequent decision to end a pregnancy, or even a relationship – but surely better at that point than for one or other parent to conclude later that they cannot or do not want to cope. At very least it would mean that if the couple decide to have children, they are forewarned and so forearmed.

With Alzheimer's, it is not just that knowledge about the genetic components is still at a very preliminary stage, but that the possibilities even for slowing, let alone preventing the onset of the condition, are extremely limited. If you submit to screening at, say, the age of 40, and learn that you have a predisposition, to some unknown degree, to Alzheimer's, what are you supposed to do about it? It is difficult not to believe that the awareness alone would not in some way overshadow your whole life, as you kept watch for seemingly tell-tale symptoms. If and when an effective treatment is developed, through drugs or gene therapy, the calculation will change. But even at the speed with which the science of genetics is advancing, prevention or cure looks many years away.

At least a system of universal access to healthcare, such as most European countries maintain in one form or other, obviates the other great risk that arises from genetic testing. It was President Clinton who decreed that commercial health insurance companies in the United States should not be able to weight policies according to the results of genetic testing. As genetics advances, however, the line will be ever harder to hold, as insurers press for the knowledge that holds the key to certain profits. This is why the US health insurance model, even as liberalised by Barack Obama, is likely one day to become unsustainable, as it seeks to lock out those predisposed to develop one expensive debilitating condition or another.

Regardless of the uniquely ruthless US health insurance system, however, it is worth asking whether there is not something unethical about offering people genetic tests for conditions that are not – or not yet – treatable. This is not a problem with pre-conception testing, as the question posed is quite different, and, whatever the results, there is a remedy. But what about genetic testing for Alzheimer's?

As someone whose husband has what may well be an inherited form of Parkinson's disease, where genetic research seems to be at a similar stage to that of Alzheimer's, I am not sure what practical purpose testing would serve. When we married, the burden of scientific opinion was that Parkinson's was not inherited. His own family history suggested otherwise. Now, much of the research being conducted around the world is geared towards identifying genetic mutations, with one – known as LRRK2 – strongly associated with a strain of Parkinson's that manifests itself long before old age. It is possible to test for this.

At the World Parkinson's Congress, held in Glasgow last year, an American radio journalist recently diagnosed with the condition, who had a father and a brother who were also sufferers, described his dilemma on being offered such a test. After consulting close family, he declined. He never actually said why, and maybe his grown-up children feared pressure to be tested, too, and the possible effects of such knowledge on their quality of life and insurability. But it is possible to imagine, too, that, with no treatment available, he felt the scales of advantage weighted against him. Altruism might militate in favour of taking a test, for the sake of medical research; his own long-considered preference was not to know. And who can blame him? Perhaps it is part of the human condition not to bow to determinism until you have to.

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