Molecular genetics of human major histocompatibility complex: clinical applications.

Techniques in molecular biology have proved to be very useful in the study of the biology and genetics of the MHC. In particular we have been able to study the Class II gene region in more detail. It is very important because most of the clinical interest of MHC has been focused on the Class II: Certain Class II alleles are strongly associated with autoimmune diseases, and Class II molecules play a crucial role in the interactions between the cells in immune response. DNA polymorphism studies (RFLP) have shown us that polymorphism of MHC genes seems to be considerable. Other close associations between diseases and Class II markers than using serological HLA typings have been found. Molecular cloning of the Class III genes has allowed us to analyse the molecular basis of the complement protein deficiencies, which are often associated with autoimmune diseases. Furthermore, cloning of the genes coding for steroid 21-hydroxylase has revealed the reason for the linkage between CAH and HLA, and has given a possibility for prenatal diagnosis of this disease at the DNA level.