Yes, it's hard to resist the quip that the headline would better be "High proportion of transgender patients found to suffer from other mental health issues".
But that's not just a quip. Obviously having this sort of belief in being "transgender" (ie somehow being the "wrong" sex, or being in the "wrong" body, or being "wrong" for your sex) is a symptom of some sort of problem. It's incredibly likely that the "mental health issue" is indirectly the either the cause of the identification as transgender, or is comorbid with an undiagnosed cause.