BPD is usually caused by some sort of childhood trauma like abuse, neglect ect. Everyone experiences trauma at some point but if you are already predisposed genetically to Bipolar Disorder by a family member having the diagnosis it can make you more susceptible to developing BPD. I have BPD and Schizoaffective Disorder along with ADHD. I developed BPD from severe childhood trauma. The condition was exasperated when my parents gave me to the state when I was 15 y/o.