Somatic mutations in the BRAF gene have been identified in the Langerhans cells of some individuals with Langerhans cell histiocytosis. Somatic gene mutations are acquired during a person's lifetime and are present only in certain cells. These changes are not inherited.

The BRAF gene provides instructions for making a protein that is normally switched on and off in response to signals that control cell growth and development. Somatic mutations cause the BRAF protein in affected cells to be continuously active and to transmit messages to the nucleus even in the absence of these chemical signals. The overactive protein may contribute to the development of Langerhans cell histiocytosis by allowing the Langerhans cells to grow and divide uncontrollably.