I realize Caitlyn Jenner has been discussed ad nauseam by this point, but I would like to weigh in from a slightly different angle.
In order for the feeling of gender misidentity on Jenner’s part (or any transgender’s part) to be valid, a person must be more than their mere biological body alone. Otherwise, there’d be no “real them” to be trapped inside the outer shell of their physical appearance in the first place. In other words, if, as many atheistic naturalists claim, a person is simply a collection of cells devoid of a mind or a soul, then the transgender’s frustration is delusional on its face, since there simply is no “inner you” to feel trapped within the “outer you” (because the latter is all there is). But if those with a more religious and/or supernaturalist worldview are correct about humans being both a body and a soul, then there’s a basis for understanding the transgender’s frustration—such people actually have a lexicon and vocabulary to deal with such claims, and a framework for beginning to try to understand them.