Here's a young woman who had nothing medically wrong with her, but who had both of her breasts removed because breast cancer ran in her family. She had a genetic test that said she was 85% likely to develop breast cancer.
https://www.youtube.com/watch?v=Pvo8JrZSaM8
Watch that documentary replacing "breasts" with "penis", and "double mammectomy" with "penectomy", and try to imagine if you were considering a penectomy because the doctor told you you had the gene.
Go.