Genetic tests: sometimes useful, often dodgy
Not so long ago ‘genetic testing’ was more or less confined to generally rare, single-gene disorders – for example, the childhood onset muscle-wasting disease Duchenne muscular dystrophy, or Huntington’s disease, a progressive nervous system disorder that usually starts to affect people in middle age. Genetic tests are done to diagnose such conditions but can also be used to screen healthy people whose family history indicates that their chances of developing the disorder in question are above average, and to guide their family plans.
However, most diseases cannot be attributed to a single faulty gene. Usually, diseases depend on the way in which risk variants in several genes interact, and on the interaction of these genetic risk variants with environmental factors. Only when there is a ‘critical’ combination of genetic risk variants and environmental factors will a disease become apparent.
Don’t play poker with your genes
Acting on the knowledge of a single (or even a few) gene variants is similar to betting all your money on a poker hand when you’ve only seen one card.
This ‘do-it-yourself ’ approach clearly does not meet the criteria for a useful screening test. However, the result may well make you anxious and decision-making difficult, and may have wider implications too – on members of your family, for example. As one Australian health journalist put it ‘For anyone concerned about the creeping medicalisation of life, the marketplace for genetic testing is surely one of the latest frontiers, where apparently harmless technology can help mutate healthy people into fearful patients, their personhood redefined by multiple genetic predispositions for disease and early death.’ 
Next: What screening aims to achieve and why evidence matters