There is a psychological disorder called
Body Integrity Identity Disorder. Basically, you hate a body part and want to have it amputated. The majority of people with this condition are middle aged white males like Jenner.
It is not treated by amputation, unless you hate your genitals, in which case you are called "transgender" and have your genitals amputated and facsimiles of genitals of the opposite sex constructed in their place.