A SNP of KIT exon ten, encoding for the substitution of a methionine in position 541 by a leucine (KITL541) in the mature KIT protein, has already been reported to be associated with several diseases, including aggressive fibromatosis (AF) [13–15], chronic myelogenous leukemia (CML) [16], pediatric mastocytosis [17] and more recently in chronic eosinophilic leukemia [18]. This evidence concerns the gene KIT and mastocytosis.