RecruitingRegistry for Patients With Erdheim-Chester Disease and Other HistiocytosesThe investigators want to understand more about what kinds of health problems are caused by histiocytosis, what happens as a result of different treatments, and how ECD affects people's lives, their feelings and their attitudes. The investigators also want to learn how these things change over time for people with these conditions. To try to figure this out, doctors would like to collect information about people who have histiocytosis and how they are treated for this disease. Some participants will be asked to complete a brief interview over the telephone. Only a limited number of interviews will take place, and not everyone will be asked to participate in the interview. It is okay if the participant does not want to participate in the interview portion. If this is the case, the participant should let the study team member know when contacted.