Complex sentence: Addison's disease arises from problems with the adrenal gland such that not enough of the steroid hormone cortisol and possibly aldosterone are produced, most often due to damage by the body's own immune system in the developed world and tuberculosis in the developing world.
Split into simpler sentences: Addison's disease arises from problems with the adrenal gland such that there is not enough of the steroid hormone cortisol and possibly aldosterone. This is most often due to damage by the body's own immune system in the developed world and tuberculosis in the developing world.