Due to differences in the genes that control the HPA axis, however, other people may fail to have a strong enough response to a threat, while still others may over respond to even minor threats.
Over-response being overproduction of aldosterone (and cortisol) in reaction to stress triggered ACTH.
From same page
Beyond biological differences, the HPA axis also can alter its functioning in response to environmental influences. The HPA axis may permanently be altered as a result of extreme stress at any time during the life cycle — during adulthood, adolescence, early childhood, or even in the womb.
If there are major stresses in early childhood**, the HPA feedback loop becomes stronger and stronger with each new stressful experience. This results in an individual who, by adulthood, has an extremely sensitive stress circuit in place. In life threatening situations — such as life in an area torn by war — this exaggerated response would help an individual to survive. In contemporary society, however, it usually causes the individual to overreact hormonally to comparatively minor situations.
**Why just in childhood? Wouldn't this apply to any age??