Can Bipolar sometimes mimic sociopathic behavior?

I'm asking because my nephew was diagnosed bipolar around 16 yrs of age, who now seems to fit the profile of a sociopath. He has repeatedly lied and stolen from my sister and has had more second chances than I can count. She had thrown him out a while back and he was living with a friend's family. She took him back a few weeks ago after he apologized once again and vowed that he was getting his life on track again. His meds are supposedly balanced. When my family went to visit my sister's family a couple of weeks he went out of his way to be overly friendly and helpful. My sister really thought he meant it this time. It seemed a little over the top to me to be honest. It made me kind of uncomfortabe. A day after we left she found out he stole money and electonics from her to pay for illicit drugs. She also found knives and scissors hidden througout his room. She ended up telling him he had to check into a rehab program or she would get the police involved. He is at a hospital right now and I am hoping that his behavior is a result of an addiction that can be overcome. My sister told me she thinks he's a sociopath and I just read the definition. It sounds about right. Apparently there is no medication that can help it or therapy that has been proven successful? Can any of you tell me if you or your loved ones have ever experienced this as part of the bipolar disorder or maybe because of the combination of illicit drugs and prescription drugs? I am so worried about my sister's safety. She says she's kicked him out for good this time, but she is so kind hearted and I know she wants to believe he can change. I am scared that even if she doen't invite him back into the house that he might harm her in some way.

Thank you so much It's genetic! I will check out that online information. Thank you as well karen. My sister is not able to speak with the doctor because her son, who is legally an adult, will not give her permission to do so. Her husband has spoken to their son and the only information they are getting right now is coming from the son. The hospital he's at will not release any information to my sister so for all they know he might not even be there.

Thanks Voix. I really hope it is the addiction. At least that way he can get help and no problem Genetic.