Disease taxonomy--polygenic.
The practice of medicine depends on the recognition and classification of disease. Correct diagnosis is the cornerstone of correct treatment. The past century has seen the classification of disease move from a reliance on symptoms and signs to the use of more and more sophisticated measurements of human structure and function. However, although most diseases have now have names and schemes of classification, these names still may hide a fundamental lack of understanding of the causes of the disease. The extraordinary progress in molecular genetics in the last 20 years now means that a complete understanding of the constitutional predisposition to disease is possible. All disease results from the interaction between adverse environmental events and constitutional (genetic) resistance or susceptibility. Genetic resistance is modified by ageing. The study of genetics is the process of linking polymorphism in the genetic material to polymorphism or variation in the function or appearance of an organism. The extent to which this becomes clinically useful will be determined by the strength of the genetic effects influencing the disease. Oligogenic disorders, in which just a few genes are impacting on the disease, are more likely to be classifiable by genetic polymorphism than true polygenic disorders, in which a multiplicity of small effects give incremental risks of developing disease. Nevertheless, an improved understanding of the aetiology of disease will in all probability identify previously unrecognised yet distinct subsets of disease.