In LCH disease with wild type BRAF, recurrent mutations in the MAP2K1 gene can be found in up to 50% of cases [46,47], substantiating a role for mutant RAF-MEK-ERK drive, either via BRAF V(600)E or mutated MAP2K1 in LCH pathogenesis. This evidence concerns the gene MAP2K1 and Langerhans cell histiocytosis.