YOUR editorial ('The genetic tyranny', 18 July) rightly concludes that as knowledge of human genes accrues, we need to consider the ethics of how these breakthroughs are applied. However, it focused on the negative quasi-eugenic potential of genetic research. While we must, indeed, forestall any abuse of the new knowledge, for most workers in this area the goal is not genetic selection but to gain insights into disease mechanisms so that cures can be designed. For many of the complex diseases with a genetic component - diabetes, multiple sclerosis, arthritis, cancers - the main problem is that we don't understand enough about what's gone wrong to prevent it or put it right. Identifying the culprit genes and learning what they do is the key to new cures - in many cases perhaps simply putting back a missing or faulty chemical.