They carry susceptibility and resistance to diverse diseases, including deficiencies of CYP21 hydroxylase (47.1) and complement components (18.1), as well as numerous autoimmune diseases (8.1).
A conformation-dependent epitope in Addison's disease and other endocrinological autoimmune diseases maps to a carboxyl-terminal functional domain of human steroid 21-hydroxylase.
Frequent gene deletions and duplications have been described in the C4 and CYP21 genes, particularly in patients with autoimmune diseases and congenital adrenal hyperplasia.