Immunology and clinical manifestations of non-clonal mast cell activation syndrome

There is a spectrum of disorders that clinically manifest as a result of mast cell activation. A non-clonal form has emerged in the literature where many of the clinical features of systemic mastocytosis are shared despite having a distinct mast cell biology. In this review, we summarize key features of the science behind mast cell activation relevant to what is now known as non-clonal mast cell activation syndrome (nc-MCAS). We highlight the clinical manifestations of nc-MCAS with a focus on diagnosis and treatment.