In the case of the HPA axis, both mechanisms occur—mice that were implanted with CRH‐secreting tumors showed both corticotroph hyperplasia and hypertrophy (Asa et al, 1992), and chronically stressed rats showed both adrenal hyperplasia and hypertrophy (Ulrich‐Lai et al, 2006). The gene discussed is CRH; the disease is hyperplasia.