"In 2008 Dr. Afrin started coming to understand that a newly recognized type of mast cell disease, now called mast cell activation syndrome (MCAS), was the underlying diagnosis in many patients he was seeing who were each suffering large assortments -- quite different from one patient to the next -- of chronic multisystem inflammatory illnesses of unclear cause. Dr. Afrin soon gained experience that MCAS is far more prevalent than the only mast cell...