In people suffering from a rare disease the diagnostic process and the confirmation of a final diagnosis is often ongoing for many years. Factors contributing to delayed diagnosis include the limited knowledge of health care professionals about rare diseases and their symptoms but also a psychiatric or psychosomatic (co-)morbidity obscuring the symptoms of the rare disease. The project ZSE-DUO will evaluate whether a combination of an expert in somatic medicine and a psychiatric/psychosomatic specialist will increase the rate of assured diagnoses in patients approaching a center of rare diseases (primary outcome), accelerate the process until a diagnosis is made, reduce the costs of diagnosing a patient, and lead to a higher satisfaction of patients and health care professionals. Furthermore, the project will evaluate whether the use of psychosomatic screening tools at registration of a patient in a center for rare diseases will help to guide the diagnostic process. Two cohorts of 682 patients each will be sequentially recruited over 9 plus 9 months: the Control group cohort (CG based on somatic expertise) and the Experimental group cohort (EG combined psychosomatic/somatic expertise Included will be persons from the age of at least 12 years presenting with symptoms and signs which are not explained by current diagnoses (as judged by the patient's primary care physician and a specialized physician at the center for rare diseases ZSE evaluating the medical records). Patients will be recruited from 11 German Centers for Rare Diseases associated with University hospitals in the cities of Aachen, Bochum, Frankfurt, Hannover, Magdeburg, Mainz, Münster, Regensburg, Tübingen, Ulm and Würzburg. Recruitment will be supported by a collaboration with the German patient organization representing many rare disease organizations ACHSE e.V. and a collaboration with the insurance companies Techniker Krankenkasse, IKK gesund plus and AOK Hessen who also provide data on costs of care. Data collection and analysis will be coordinated and performed by the Institute for Clinical Epidemiology and Biometry at the University of Würzburg, the Institute for Epidemiology, Social Medicine and Science of Health Care Systems in Hannover, and the Department of Medical Psychology in Hamburg. The project is funded by the Innovationsfond of the Federal Joint Committee in Germany.

Inclusion Criteria:

• first contact with the Center for Rare Diseases for unclear diagnosis
• suspicion of a rare disease but no established diagnosis
• attending the Center for Rare Diseases as an outpatient
• written informed consent

Exclusion Criteria:

• age <12 years
• incomplete medical records including summary letters, imaging studies, blood tests etc.
• pre-diagnosed disease(s) explaining all symptoms