Monoclonal Mast Cell Activation Syndrome

**Semantic type:** Disease or Syndrome

**Definition:** A rare immunological disorder characterized by mast cell activation in the absence of cutaneous findings. Bone marrow biopsy shows the presence of monoclonal mast cells that carry the D816V KIT gene mutation and/or express CD25 while not meeting the diagnostic requirements for systemic mastocytosis. Patients may present with recurrent symptoms, including hypotension, flushing, headache, abdominal cramping, nausea, diarrhea, arrhythmias, and bronchoconstriction. Symptoms may be triggered by eating, exertion, environmental conditions, emotional stress, or insect stings, and treatment may include antihistamines.

**Synonyms:** - MMAS