Genetics of the complement system

After a brief history of complement genetics, general considerations and applications to our understanding of immune function, evolution, population structure and migration and forensic medicine, selected topics in complement genetics are presented. For individual complement proteins, genetic polymorphisms and deficiency states are described, as are the molecular bases of some of them. The clinical abnormalities exhibited by some patients with complement deficiency states are discussed, as are possible pathophysiologic mechanisms for them. The chromosomal location and the close linkage and a sharing of structural features by groups of complement proteins, such as the complotypes of the major histocompatibility complex, the regulators of complement activation, Clr and Cls, and the terminal components C6, C7 and C9, are presented in some detail. From these facts, the broad outlines are drawn of the evolution of the classical and alternative complement pathways from the lectin pathway and the terminal pathway from a common progenitor. From markers within the complotype region, rough conclusions are delineated regarding the evolution of C2, factor B, C4A and C4B alleles.