Biological individuality and disease. From Garrod's Chemical Individuality to HLA associated diseases.

The concept of "predisposition" in medicine is ancient, and the term "diathesis" was used to express it since the days of Hippocrates and, especially, of Galen. The concept of diathesis was enormously popular throughout the nineteenth century, despite the vagueness of its actual meaning. It was clarified only in the early years of the twentieth century (1902), when it was however losing its clinical relevance, by a replacement of the concept of chemical individuality by A.E. Garrod, followed thirty years later by the concept of inborn factors in disease (1931). "Molecular" knowledge of the biological individuality of human beings, highlighted particularly by the discovery of the MHC (Major Histocompatibility Complex) during the last 30-35 years, and substantially HLA (Human Leukocyte Antigens), has offered a new and better understanding of the relationship between the self and the not-self, as well as of various diseases, especially if they are favored by some immune dyshomeostatis. Extensive knowledge of transplants--their "immune" fate of take or rejection, possibly of GVHD--have allowed mankind to consider each human being as a biological Ego, unique in his antigenic-molecular structure. But most of all, the demonstration of the fact that certain HLA antigens can be significantly associated with a greater predisposition, on the part of individuals bearing these antigens, toward contracting certain diseases, reconsiders in precise molecular terms the concept of "predisposition" and therefore, perhaps, in a new light, even the concept of "diathesis", providing an actual logical basis for it.