Genetic studies in CM and SM have focused on genes encoding cytokines and their receptors (IL13, IL6, IL6R, IL31, IL4R) or on genes encoding Toll-like receptors (TLRs) [26,27,28,29,30].However, given the rarity of mastocytosis only small numbers of patients have been studied and more studies are required to draw definitive conclusions regarding the impact of these genetic variants on phenotypes and outcomes associated with mastocytosis. This evidence concerns the gene IL4R and mastocytosis.