In my family there is a strong genetic predisposition. I myself see the

that I and those I love have.
When you have a child with BPD they need a validating environment, they need their hypersensitivity recognised and managed, they need sound values based boundaries from both parents in agreement. My dd had a loving validating family environment but it wasn't enough for her. The validation was always tempered with logic and exhortations for her to do well... . seen as encouragement. By her probably seen as her not ever being good enough, was definitely seen by her as controlling and was seen as emotionally abusive. Dh and I were not in agreement on the boundaries, I was 'strict' he was 'permissive' - there was no consistency there. Her sensitivity wasn't appreciated.
And the world around us was even more invalidating, permissive and harsh. A world that looks to blame someone for when things go wrong.
Couple this with some key incidents that occurred at important times, eg at 18 her dad was near death awaiting a transplant and had been 'dying' for a year... .
Stand strong bioadoptmom - we are the wise ones here it's just our BPD kids got the wrong combination of genes, environment, culture and traumatic events and we weren't equipped to cope with it. Don't beat yourself up, ok?
Vivek
ps things may look shiny on the outside looking on, but in another person's reality, it might not be so squeaky clean - I am only human, I made mistakes and I didn't even know.