In screening for genetic mutations that can cause disease, the line between useful and damaging knowledge is hard to draw. We can in many instances find out who will fall victim to conditions for which no treatment exists. Huntington’s chorea is caused by a single mutation that can easily be identified. The case of cystic fibrosis (CF) is similar. Those who inherit a CF-related gene mutation from each parent will always go on to develop the condition, and will die from it unless they die from another cause first. No one who does not have a CF-related mutation will develop the disease. Some symptoms can be ameliorated temporarily, but though the etiology and development of both afflictions are well understood, there is no way to prevent either of them.1 Hereditary prion diseases—genetic neural conditions caused by misfolded proteins—are rarer, but likewise play out with grim reliability. No treatment can slow the inexorable progress toward an agonizing death.
Bioethicists disagree on whether diagnoses of such diseases should be postponed until symptoms develop or should be made much earlier, even in infancy. More and more, clinicians argue that diagnosis before the onset of symptoms can benefit patients. It can circumvent an exhausting investigative odyssey; it can inform reproductive decisions; it can help a patient to plan; it can allow him or her to connect with others with the same condition, which is not only reassuring for the patient but also helpful to research scientists. But it can also cause despair. To what extent is information about an unpreventable genetic disease that has not yet caused any symptoms a gift and to what extent is it a burden?
This double-edged sword of genetic testing hangs over Gina Kolata’s Mercies in Disguise. Kolata, a well-known reporter on science and medicine for The New York Times, is a gifted storyteller. Her account of the Baxleys of South Carolina, a family with Gerstmann-Sträussler-Scheinker disease (GSS), is both engrossing and distressing. GSS is a rare hereditary prion disease symptomatically similar to Alzheimer’s mixed with Parkinson’s. All those who test positive for the mutation will develop the disease unless they die younger of other causes. The age of onset is between thirty-five and fifty-five, and once the disease sets in, the average survival period is five years, though some people live longer.
Those affected lose their sense of balance; they develop constant shaking; they become unable to walk and ultimately to control their movement at all; their speech becomes slurred, then incomprehensible; they find themselves unable to chew and swallow food; they cease to recognize their spouses and children;…
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