Agree with Trills that it is inherited through being learned/t(?) (tired sorry)
My DS is similar and my Ex has not been diagnosed as having NPD but after extensive counselling myself, My counsellor has said it is highly likely he would be he were to be assessed.
It is taking time but DS is unlearning the behaviour he picked up, we deal with the situation that occurs, and then sit and talk quietly when all is calm and I ask how he feels about, and sees his own behaviour, and he himself sees that it mirrors how his Dad is.
The 6 weeks holiday has been a mix of pure hell and also some (hopefully) key steps forward. Especially in how he treats his 8 yr old sister, as very often it mirrored the crap his Dad put him through.
When DS gets upset about something not going his way, all the emotions and issues from the past bubble up and we will often get anger about his Dad as well. Like the initial incident catches and knocks off a scab and then al the gunk behind it comes to the surface.
I try, (but sometimes fail through frustration) to nurture his positive qualities. Sometimes through threats to remove privileges if he doesn't try harder to self moderate, through rewards, praise and thanks when he really 'gets it' and also massively by appealing to his sense of self and who he wants to be. Telling him that it is a process he is going through but that I believe in him.
As it is liberally sprinkled with teen angst, it is, quite frankly, exhausting, but as we make progress and I look back to different stages in the past, it is brilliant to see that overall, he is becoming a fine young man.
My DS lacked empathy, but I think a part of that was that his Dad had done so much damage, and blamed him for so much, that in a way DS had switched off many emotions, and could only express himself through anger, and he seemed unable to process feelings like disappointment, hurt, fear, without it triggering all the rage and his own hurt inside . I have talked a lot to him about how other people (his sister) feels the same emotions as him and he seems to be connecting with that.
My heart goes out to you, I am so sorry to ramble, but if anything helps.....