The long tail and Rare Diseases:

1. TTL Project Marathon Rare Disease and Social Media: an opportunity for the long tai l Manuel Armayones Ruiz, PhD Assistant Professor Psinet Research Group- Internet Interdisciplinary Institute Open University of Catalonia (Spain) [email_address] http://in3.uoc.edu/opencms/opencms/webs/grups_de_recerca/psinet/CA/

2. A disease or disorder is defined as rare in Europe when it affects less than 1 in 2000 citizens (Orphan Drug Regulation 141/2000). Rare diseases may affect 30 million European Union citizens . Rare diseases are characterised by a broad diversity of disorders and symptoms that vary not only from disease to disease but also from patient to patient suffering from the same disease. Relatively common symptoms can hide underlying rare diseases, leading to misdiagnosis .