Personalized Medicine: Some Thoughts

is increased rate of metabolism of a drug after it has been given; the drug has increased the activity of the gene that controls its metabolizing enzyme. Another example: an alcoholic is a person whose original consumption of alcohol has affected a gene in the brain that affects the wish to drink more of it. Since innumerable internal and environmental factors may affect gene expression, a person's set of genes is never constant but always more or less changing. This makes it impossible to exactly predict the activities of a person's genes. However, not all genes change their expression over a given time. There must be a likelihood that a set of genes studied a week apart is more similar than when studied a month or a year apart. We do not know whether a set of genes remains more constant over time within person A than within person B. Thus, at the present time, dealing with gene expression is usually a matter of probability, and perhaps never or rarely of certainty. Consequently, when dealing with gene expression and with future drug responses, one is dealing with matters of probability. By the same token, we can never precisely predict the effect of a drug on a person, although it often remains identical over reasonable periods; prediction of the effect of a drug is a matter of probability, and thus is 'personalized medicine'. In short, there have been some steps made towards personalized medicine, but it will never be a reliable entity; it is an entity of probability. FEATURE REVIEW