Authors analyzed association of mastocytosis with two variants in promoter IL31 gene (−1066 G > A (rs 11608363), −2057 G > A (rs 6489188), and one in intronic region (IVS2 + 12A > G) and found that −2057AA genotype is associated with a high prevalence of mastocytosis (CM and SM) in adult patients. This evidence concerns the gene IL31 and mastocytosis.