Genetic Linkage Studies Have Identified Numerous Genes in Which Certain

Genetic linkage studies have identified numerous genes in which certain polymorphisms are associated with a predisposition to autoimmune disease. Yet in most cases, the effects of individual genetic polymorphisms are very small, with each one being linked to a very modest effect on disease incidence. This indicates that:

A) The genetic data are not providing useful information about genes involved in immune regulation.
B) Autoimmune diseases can be caused by many different single gene defects.
C) Many different environmental factors are determining which predisposed individuals develop autoimmunity.
D) It is unlikely that autoimmune disease incidences would be increased in particular families.
E) Individuals with particular genetic backgrounds would have the same likelihood of autoimmunity regardless of where they reside in the world.