Mastocytosis – a disease with many faces

Published Online: April 15, 2013

Mastocytosis is an uncommon disease characterized by increased numbers of mast cells in the body. Mast cells are cells mainly involved in the allergic reaction in humans. The reason for accumulation of mast cells in mastocytosis is most often an acquired mutation in the KIT gene – a gene encoding a cell receptor involved in the regulation of growth and maturation of mast cells. The KIT mutation leads to de-regulated mast cell growth and an expansion of a clone of neoplastic mast cells. The majority of adults with mastocytosis have the non-aggressive, indolent form with a normal life-expectancy. Symptoms in indolent mastocytosis can be very heterogeneous and are mainly caused by release of mediator compounds from the mast cells, such as histamine. The explanation for the variable symptoms in mastocytosis is not clear, especially regarding whether patients with a higher burden of cells carrying the KIT mutation in fact suffer from more severe symptoms or poorer prognosis.

In an Original article in The Journal of Allergy & Clinical Immunology (JACI), Broesby-Olsen  et al presented data from 48 adult patients with indolent mastocytosis in which they tried to correlate the type and severity of clinical symptoms to the level of KIT mutation-positive cells as determined by a sensitive method for detection of the KIT mutation recently developed by the authors. Included patients were evaluated for symptoms from the skin and gastrointestinal tract, musculoskeletal pain, neuropsychiatric symptoms, occurrence of osteoporosis, as well as anaphylactic episodes.

The authors found that severity and type of symptoms did not differ significantly between patients with different levels of KIT mutation positive cells. Apart from indications of a longer disease duration and higher age among patients with higher burden of mutated cells, no significant differences could be observed. The authors suggest that these findings may reflect that the KIT mutation in mastocytosis is often carried by non-mast cells or non-mature mast cells to a varying degree, and that the mutation burden thus does not solely represent neoplastic mast cells. The study is the first to demonstrate the clinical impact of KIT mutation burden. Findings do support a treatment strategy in indolent mastocytosis aimed at blocking the release of mediators from mast cells, whereas therapies aiming at reduction of the mutated cells, that commonly have side-effects, should be reserved for the rare, aggressive forms of mastocytosis.

The Journal of Allergy and Clinical Immunology (JACI) is an official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.

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