I think you are born with the really bad personality disorders - sociopathy and psychopathy - brain scans of these people show very low activity in certain areas of the brain - as if that bit didn't form properly. some work can be done to improve them but as it usually discovered in adulthood, most of the potential to change it as the brain develops has been lost.
Suffers of post traumatic stress disorder also seem to have brain activity that is not normal - they have a low ability to recognise sadness and fear complared to the genral population - as though their experiences have shut down parts of the brain - these people can be helped but suffer dreadfully.
Some people learn abusive patterns by being abused themselves, alhtough it is not a hard and fast relationship (otherwise everyone released from WW2 concetration camps would have turned into murderers and sadists and this did not happen).
Personality is shaped by experiences - but you can't turn an extrovert into an introvert without some kind of massive life trauma.
So some behaviour is learned and some you are born with. Some things can be taught and some behaviours modified - for instance I am a very angry person, but I do not express my anger publicly or hit people - becuase I have been taught this is wrong, and I moderate my behaviour within socially accepted norms. If I had not been taught these when a child I probably would shout and scream in the street and hit DD on a regular basis - but I don't, and never have. When I feel an anger burst I walk off, and only discuss issues after I've calmed down. I am self aware - abusers lack self awareness I think, and also never consider other people as human, or worthy of consideration. empathy should develop in childhood - but for some it gets stunted or just doesn't happen.
My DD is a lovely happy child - if hse was told daily she was crap and worthless and was hit regularly, I have no doubt her personality would be very very different - as she would have to develop defence mechanisms.