Overall, 9/10 patients had WDSM according to recently proposed criteria [19] consisting of histologically-proven mastocytosis in the skin and BM compact aggregates of mature-appearing CD25−/low/CD2−/low MCs, together with clusters of ≥ 2 MCs outside BM particles (n = 9), aberrant expression of CD30 and/or overexpression of cytoplasmic proteases (n = 4), mutations involving exons other than exon 17 of KIT (n = 3), a clonal HUMARA pattern of inactivation of X chromosome (n = 3), and/or female sex with either pediatric disease onset (n = 7) and/or familial aggregation (n = 4). The gene discussed is TNFRSF8; the disease is mastocytosis.