I think it's possible to be taught areas or certain styles of art, not necessarily portraiture. It helps to have an innate gift for creativity in order to appreciate the esthetics of art. It's not just about picking up a pencil and drawing a picture, a lot of thought must go into a project - and continue to flow to completion.
I taught a Life Drawing/Portrait class. Many of my students came into the class gifted and talented, and took the class to brush up on their skills. I had a couple of students who were artists in other areas and were trying to learn portraiture. They found out very quickly, though, that it's not something you just decide to do, it takes time, dedication, and skill.