One of the things that an endocrinologist treats is hormonal sexual dysfunction and may not have studied transgender origin and is just giving you her/his opinion from her/his understanding, without the knowledge about the research.  Research on cadavers shows opposite sex brain structures in transgender people.  The origin is from pre birth.  The brain was formed differently and the theory is that biologically it happens at conception or at the 8 week mark of pregnancy.  The article is correct.  A endocrinologist or any doctor should know the difference between assumption and knowledge gained from studying and research.  Your endocrinologist made quite a leap in judgment.  Just because you have an area of knowledge doesn't mean you know everything about a specific specialty withint that field.  This is why we have the judgmental society with have.  Doctors giving opinions like it is fact.