The use of CYP21 fragments and mouse monoclonal antibodies emphasized the antigenic relevance of the middle and carboxyl-terminal regions of CYP21 and resulted in the detection of two short amino-acid stretches (CYP21335−339 and CYP21406−411) as the main epitopes independently from patient disease (sporadic AAD, APS1, APS2, and isolated CYP21-Ab positivity) (311, 312). This evidence concerns the gene CYP21A2 and autoimmune polyendocrine syndrome type 1.