Introduction J-F. Cordier Correspondence: J-F. Cordier, Dept of Respiratory Diseases, Reference Center for Rare Pulmonary Disease, Louis Pradel Hospital Claude Bernard University, Lyon (Bron), 69677, France, email: jean-francois.cordier@chu-lyon.fr C hest physicians may sometimes feel that they are not directly concerned by rare or so-called orphan lung diseases, supposing such diseases are reserved for specialists working in university centres. However, this is not true as patients with such diseases are distributed throughout the country, and can begin their diagnostic trajectory close to the place where they live. Thus, any chest physician will meet several patients with rare diseases during his career. The term ‘‘orphan’’ disease means that affected patients feel that almost nobody cares about their disease and that none or little research is performed to improve diagnosis, clinical management, and to elaborate or commercialise drugs to treat the condition. The patient, therefore, feels abandoned and as such like an ‘‘orphan’’. Orphan diseases may commonly be neglected but can be frequent diseases in low-income countries, especially tropical diseases, such as trypanosomiasis. As the population of such countries does not have the money to buy drugs, many pharmaceutical companies are reluctant to invest in research for these non-solvent populations. In most developed countries orphan diseases are largely rare diseases that are little known to the public and even to doctors. A disease is defined as rare in Europe if it affects less than one in 2,000 persons. However, this definition covers a strong disparity, as some disorders affect several thousand or tens of thousands of patients, whereas others affect only a few hundred or even a few dozen patients throughout Europe. Approximately 8,000 different rare diseases have been identified, 80% of which are considered to be of genetic origin. If most of the rare genetic diseases are present at birth or during childhood, others may manifest only at adulthood. Furthermore, the clinical phenotypes of the rare diseases may be varied, thereby complicating diagnosis and care, particularly when several organs are involved. Patients with rare disease feel orphaned in the healthcare world and a lack of solicitude. They are often disappointed and angry by failure to diagnose or misdiagnosis, which can occur for months or even years before they eventually find an experienced clinician. Diagnosis is especially difficult when the disease imitates a more common disorder. Furthermore, as teaching in medical schools cannot cover the many rare diseases it is unavoidable that general practitioners do not know all of the estimated 8,000 rare diseases. Therefore, the specialist must have the capacity to suspect the diagnosis in their own field and further orientate the patient towards expert centres, where the final diagnosis may be confirmed and the management defined, if necessary. The orphan lung diseases or orphan diseases including lung involvement have not yet been precisely indexed. Some of these are of genetic origin (e.g. hereditary haemorrhagic telangiectasia), others are acquired, systemic diseases that comprise pulmonary involvement (e.g. vasculitis), whilst others only concern one sex (e.g. sporadic lymphangioleiomyomatosis, which affects only females). Some orphan diseases have become just rare diseases because dedicated research has resulted in efficient drug discovery and commercialisation (e.g. idiopathic pulmonary arterial hypertension). The interest of chest physicians for rare/orphan diseases has increased, over recent years, for several reasons. These include, amongst others, the advancement of diagnostic tools e.g. Eur Respir Mon 2011 54: vii–viii. Printed in UK – all rights reserved. Copyright ERS 2011. European Respiratory Monograph ISSN: 1025-448x. DOI: 10.1183/1025448x.10021611 vii