The PNW is the home of the Ingersoll Gender Center, which has a long history as among the first places in the US that people could go for treatment for gender-related dysphoria. I'm not sure, but guessing from the name of the center, it may have some connection to the first trans-gender surgeries done in Denmark. There are loads of Scandinavians in Seattle, so it seems like a natural place for this field of medicine to have spread to in the U.S.