KMT2A and Langerhans cell histiocytosis: AF10, ALL1-fused gene from chromosome 10 protein; AML, acute myeloid leukemia; ATG, anti-thymocyte globuline; BFM, Berlin Frankfurt Münster; CD, cluster of differentiation; FAB, French-American-British; FISH, fluorescence in situ hybridization; GvHD, Graft versus Host Disease; hSCT, hematopoietic stem cell transplantation; LCH, Langerhans cell histiocytosis; MLL, mixed lineage leukemia; PCR, polymerase chain reaction; PPNH, persistent pulmonary hypertension; RT-PCR, real-time PCR; TMD, transient myeloproliferative disorder