In the context of the European Union, rare diseases are defined as those with a prevalence of fewer than 5 cases per 10,000 inhabitants. The term “rare disease” refers broadly to a heterogeneous group of conditions, the number of which ranges between 5,000 and 8,000. Although the individual prevalence of each of these diseases is low, when considered collectively, they affect approximately 3 million people in Spain, 30 million in Europe, and 300 million worldwide. In general, they tend to follow a very severe chronic course, with multiple motor, sensory, and cognitive impairments, and therefore typically present a high level of clinical complexity. These characteristics make their management in the healthcare setting particularly challenging, especially in aspects related to diagnosis; in fact, it is estimated that patients with rare diseases take an average of 5 years to receive a diagnosis.
The IIER is a center within the ISCIII that conducts research on rare diseases from various perspectives. It has two research areas, which also provide scientific and technical services: Human Genetics and Epidemiology, each comprising several Research Units. It has been part of the structure of the Carlos III Health Institute (ISCIII) since November 2003 and is integrated into the Subdirectorate General for Applied Services, Training, and Research. The strategic objectives of the IIER align with those of the International Rare Diseases Research Consortium (IRDiRC) and the ISCIII.
The complexity of rare diseases means that a high percentage of such cases must be referred to clinical centers with a high level of specialization and, ultimately, to undiagnosed cases programs, which are characterized by conducting individualized studies of patients, involving a multidisciplinary team of professionals.
