[GoneGirl]

Here's what GLAAD says about transgender language:

GLAAD Media Reference Guide

Note in the section Terms to Avoid:

Problematic: "transgenders," "a transgender"
Preferred: transgender people, a transgender person
Transgender should be used as an adjective, not as a noun. Do not say, "Tony is a transgender," or "The parade included many transgenders." Instead say, "Tony is a transgender man," or "The parade included many transgender people."

Problematic: "transgendered"
Preferred: transgender
The adjective transgender should never have an extraneous "-ed" tacked onto the end. An "-ed" suffix adds unnecessary length to the word and can cause tense confusion and grammatical errors. It also brings transgender into alignment with lesbian, gay, and bisexual. You would not say that Elton John is "gayed" or Ellen DeGeneres is "lesbianed," therefore you would not say Chaz Bono is "transgendered."