 Burden: included patients will be asked to visit the hospital 4 times in a period of 12 months. During these visits, physical examination will be performed and blood will be obtained for serological and immunological analysis. Most of these visits are combined with routine follow-up and venous punctures of the patients. However, one extra visit to the hospital and vena puncture is expected. 5 ml extra blood is obtained four times from all patients for serological analysis. Included healthy controls will be asked to visit one plenary information meeting in the evening. Controls will have a venous punctures four times during the study, during which 5 ml of blood is obtained. These samples will be obtained at the hospital during evening clinics or at school. In a subset of patients n50 and healthy controls n10, an additional 15 ml is obtained for immunological analysis. 