With the discovery of mitogen activated protein kinase extracellular signal-regulated kinase (MAP-ERK) mutations in RDD as well as other histiocytic neoplasms, novel targeted therapy with MEK-inhibitors such as cobimetinib has been utilised in cases of relapsed or refractory disease, or in cases of RDD with central nervous system (CNS) involvement [5]. Here, WNK2 is linked to sinus histiocytosis with massive lymphadenopathy.