There has previously been debate around the pathogenesis of LCH and whether it represents a neoplastic or immune disorder, however, Badalian-Very et al.’s 2010 seminal paper demonstrated that 57% of patients have a BRAF V600E mutation (78), a finding subsequently replicated (79–82), as well as demonstration of activation of the RAS-mitogen-activated protein kinase (RAS-MAPK/RAS-RAF-MEK-ERK) pathway in nearly 100% of cases (83). Here, MAP2K7 is linked to Langerhans cell histiocytosis.