Mast cells are derived from pluripotential haemopoietic dells and are the effector cells of the immediate allergic reaction via high affinity receptors for IgE. Most varients of systemic mast cell disease are clonal and a somatic mutation of c-KIT, the proto-oncogene that encodes the receptor 260 for stem cell factor, is usually present. These mutations lead to constitutive activation of KIT which causes mast cell proliferation and prevents mast cell apoptosis. In paediatric mastocytosis KIT-activating mutations are rare. Clinical symptoms are due to the release of mast cell mediators (including histamine, tryptase, heparin, TNF-a, PGD2, cytokines and chemokines) which have both local and systemic effects, and to organ infiltration.

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