> Between April 2014 and January 2021, we administered semistructured diagnostic interviews for DSM-IV disorders to 2,212 psychiatric patients, 69 of whom reported TGD identity (ie, gender identity other than cisgender such as transgender, genderqueer, or nonbinary identity).

So the entire sample consists of psychiatric patients. I'm not sure what we can do with a finding like this, given the selection bias.