I like your thinking. You are covering a huge base. But until and unless we are privvy to all histories, blood work up and labs, we are just conjuncturing possibilities.Regarding genetic test, I do agree that it can be done. The PCP in this case has to make a decision!
What about the ones outside of IDs  like MEVF, MKD, Still's, etc. Would genetic testing be worth it for OP to ask about ?