Robbi,

My husband didn't have genetic testing done.  He had a test done in the endo's office where they took a base line draw, injected a steroid and took 2 more blood draws at one hour intervals.  They said this would flag if he was late-onset or possibly a carrier.  This was 8 years ago so I don't remember the test name.

As far as the dex vs. cortisone, the dex is longer lasting and more potent.

Good luck.