I'm not sure, but I don't think that Mayo does the testing for the skin biopsies anymore. They don't do it in their labs, I mean.
From many posts I've read over the last 12 or so years, Mayo is on the list of the good places to go for PN evaluation & testing, but...... it seems to be on the bottom of the list. Preferences for other centers seem to be higher and experiences at Mayo seem to be left wanting, in many posts.
Cornell-Weill, Cleveland Clinic, Johns Hopkins, Jack miller Center to name a few, seem to get a higher experience and test rating than Mayo.