About undiagnosed diseases

A disease is defined as rare if it affects fewer than 5 persons/10,000 in Europe, or fewer than 200,000 total in the USA. There are 7-8,000 different rare diseases (RDs) that fulfil this definition, affecting altogether about 3% of the population. One of the most critical issues of RDs is the difficulty to obtain a definitive and timely diagnosis, making undiagnosed diseases (UDs) a considerable public health burden due to the complex nature of the disease and its consequences for patient care and quality of life.

Indeed, UDs are conditions that elude diagnosis by a referring specialist for a long time and despite extensive investigations; the term can include/refer to unnamed disorders with common characteristics, phenotypically well described diseases with unknown molecular bases, unusual phenotypic variants of common rare diseases, or molecular genetic abnormalities without any clear and/or known correlation with the phenotype.

People with UDs often spend many years visiting medical centers and clinicians in different specialties across the country, at great emotional and financial cost. In 2008, the Undiagnosed Diseases Program (UDP) of the NIH in the USA first showed that the establishment of specialized centers for a full evaluation of UD patients increased the possibility of a conclusive diagnosis. To cope with UDs, an International Network for Undiagnosed Diseases (UDNI) was established in 2014 across several countries. The main aims of the network are to foster a collaborative research community under a common structured governance by engaging a growing list of research and clinical centres of excellence all over the world, to collect and share data according to well-established protocols and tools, to foster the participation of patients and lay groups, to raise awareness in the UDNI of UDs, disseminating the results of research studies. Since 2014, the UDNI has organised five International Conferences to present and discuss its promising achievements.