The genetic angle is intriguing when you research the studies.

My mother's side is where hormonal problems lay, my fathers side is autoimmune conditions. I've seen it filter through the generations, repeating constantly.
My sister's firstborn was still-born, second birth was cleft palate, third birth hole in the heart. Now i know about the MTHFR +/+ mutation these birth defects she experienced are now no longer a surprise.
There isn't a healthy one amongst us! It's part of the reason why i choose to not have children.

Regarding cortisol response, i read an interesting study on children who experienced trauma, sexual, emotional, violent etc and as adults their cortisol output to stressors was reduced. Those conducting the study were surprised how little cortisol was produced in response to stress. Particularly in those who experienced physical violence trauma.

It seems to suggest, just like with neurotransmitter receptors, there becomes a 'resistence' response to stress, thus i imagine it would take a really huge trauma to produce a surge of cortisol in such people as described above.

Also interesting is that despite the experiences being during childhood, the decades of 'no trauma' did not enable the 're-programming' of the stress response system to return to normal. It is set for life, working abnormally.

It ties in with research of war veterans diagnosed with 'PTSD'....research showed that over 80% with 'PTSD' also suffered childhood abuse/trauma.
This again shows that their stress system never normalised after their childhood trama experiences, and the experience as an adult in a war zone only compounded further an abnormal functioning HPA axis, giving them the modern diagnosis of 'PTSD', which , as most of us know is treated with psych meds which unfortunately in the majority of cases, do squat for the under-lying imbalance, which sadly is never addressed.

As Faith says, it is a roll of the dice...genetics can bring us down, or lifestyle, or exposure to horrific experiences. All we can do is to minimise the damage as much as possible!