Trans doesn't really stand up to any sort of scientific thinking.
There's a range of characteristics for male brains, and a range for female, but they overlap so much that you could never take a brain and say, "oh this is so far away from the standard for a male that it must actually be female" or vice versa.
We can observe gender dysphoria in the same way as any other condition of mental distress fixated on one bodily characteristic, but none of those are (generally) treated by removing the offending part. We don't agree with someone that their left leg is wrong and should be removed, no matter how much they believe it.
So what we're left with is a social trend to compare oneself against gender stereotypes and make a statement as to how you add up - your 'gender identity'. This is the meme bit.
I really can't understand why we need one or who thought this was a good idea.
Well, as well as the patriarchy, I blame the pop science of the 90's which was all Men Brains do X, Women Brains do Y... mostly debunked now of course.