Enzyme deficiency
Addison disease
What is missing: Adrenal cortex.
Why the signs follow
Primary failure: cortisol and aldosterone fall while ACTH climbs, because the feedback never arrives. The pigmentation is the giveaway — ACTH is cut from POMC, the same precursor as melanocyte-stimulating hormone. A secondary (pituitary) failure has low ACTH and normal color.
Written for exam preparation, not for diagnosis.