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 disease previously known to medicine (the rare disease of mastocytosis) and that most MCAS patients, once accurately diagnosed, can eventually find...