1.1.6 Late-onset multifactorial disorders
It is becoming clear that many, if not most, of the common diseases that affect the Western world are multifactorial disorders with some inherited genetic component. Some of the genes that render individuals susceptible to diabetes, coronary heart disease, hypertension and many cancers, including breast cancer, have been identified and can be tested now for the presence of mutations. Multifactorial disorders present a real challenge for genetic medicine. For example, while it may be true that there is a strongly inherited component to the form of diabetes which usually occurs during adolescence (type 1 diabetes), it is not at all clear what purpose genetic testing for such a component would serve in terms of health. This is because, currently, there is no way to stop the development of the disease.
In terms of some disorders, for example heart disease and cancer, susceptibility testing might allow doctors to advise particular patients to change their diet and lifestyle, to counteract the effects of their increased genetic risk. Unfortunately, what evidence there is suggests that the results of a genetic test may fix in a patient's mind that they are going to develop the disease anyway, no matter what changes they make. This ‘genetic pessimism’ means that giving patients the results of tests may be counter-productive.