Adoptive Mother's Feelings Of Betrayal

I am worried my adoptive mother will react the same way you did. I am 47 years old and have felt a disconnect with my adoptive parents for years. I am nothing like them, so I wanted to find out my heritage and meet my bioparents before they die. I had a wonder life and great opportunities, but something has been missing all these years. My younger brother's bio mom found him and my mother did have a nervous break down, so that is why I have been apprehensive to let my parents know that I have adoption issues. I have seen a professional, but my parents are unaware. My point is....How to we let our adoptive parents know that we have the need to know about ourselves and it has nothing to do with how we were raised or for lack of love for out parents?