Ummm. I'm no expert. I can only offer you my "understanding".

BPD: caused by genetic predisposition and childhood trauma (trauma has MANY definitions). It should not be diagnosed until an adult because the symptoms are similar to typical teenage issues. Criteria include: fear of abandonment and rejection, idealizing and devaluing relationships, unstable self-image, impulsivity, SI/SUI thoughts, mood swings, feelings of emptiness, problems with anger (rage or suppression), and stress related paranoia or dissociation. You only need 5 out of 9 for the diagnosis, but depending on when and how the symptoms present, you could still be diagnosed with borderline traits. Bascially though, BPD means that you have a delay in your emotional development. So a 20 year old might have the emotional capacity of a teen. A 30 year old might have the emotional capacity of a 20 year old. (People with BPD do catch up with emotional development with or w/o help, so it's not a death sentence if you have it ).

I'm not going to go too much into the others because I really haven't researched much.

PTSD - similar symptoms, but caused by a traumatic event that doesn't have to occur in childhood.

C-PTSD - prolonged exposure to trauma, disempowerment, captivity, or entrapment with loss or lack of an escape.

Bipolar - genetic, cycles of elevated and depressed moods

Atypical depression - actually the most common form of depression, characterized by improved mood in response to positive events.

Here's a site with good explanations:
Out of the FOG