1 Testing for genetic variations using Quantitative PCR analysis (polymerase chain reaction)

What is a drug?

All of us, at some stage in our lives, are likely to receive medication for an illness. By the age of 65, 80% of the UK population are taking a prescribed medicine and many will be receiving multiple medicines. However, many people fail to respond to the drugs they are being treated with, and in some cases the unwanted occurs: an overreaction with side effects or potentially severe consequences. What is the biological basis of this variability? This investigation will help to answer this question.

Drugs are substances that interact with biological systems and change their behaviour or activity. Most drugs are processed in the body into what are called drug metabolites. The metabolite is the active form (for example, codeine is converted in your body to morphine which in turn affects the perception of pain).

How well your body processes a particular drug depends upon many things:

• how much you have of the protein that processes that drug
• whether other drugs are present that might interfere with the processing
• how well your body absorbs or excretes the drug and its metabolites.

The effect of genetic variation between individuals results in individuals metabolising drugs at different rates. In this investigation you will examine genetic variations that contribute to the level of a particular protein that is given the abbreviation CYP2D6. This protein is important in the metabolism of almost 20–25% of the most commonly prescribed 100 medicines.

In the PCR laboratory you will perform genetic tests for two variants of the CYP2D6 gene that can have significant effects upon the level of the CYP2D6 protein it codes for and consequently on the ability to metabolise certain prescription drugs. In order to understand the significance of these variants, let’s first revise the relationship between the DNA code and the resultant protein.