Novel KIT mutation, D816_N819delinsll, in a patient with systemic mastocytosis: a case report.

Mast cell (MC) disorders result from inappropriate release of mediators and/or excessive accumulation of MCs, leading to symptoms of various organs and systems. Clonal MC disorders are defined by the presence of phenotypically aberrant and/or KIT-mutated MCs, and if aggregates of MCs are detectable, are designated as mastocytosis. Systemic mastocytosis (SM) affects mainly the bone marrow, with or without skin involvement. It is associated with the activating mutation D816V in the KIT gene. Other activating KIT gene variants are also observable in SM; activating KIT mutations are recognized as a minor diagnostic SM-criterion. We report a novel KIT variant in a patient with indolent SM, an in-frame deletion-insertion affecting amino acids D816 to N819 (D816_N819delinsll), creating an aliphatic pouch similar to that resulting from the D816V mutation, and leading to MC activation as suggested by the symptoms of the patient and the positivity for phosphorylated STAT5 in the clonal MCs.