XUEC The XUECs are Networks of Units of Clinical Expertise [Xarxes d’Unitats d’Expertesa Clínica, in Catalan] in rare diseases which seek to collaborate with each other and share knowledge. They coordinate with healthcare and social care units to provide a more personalised and efficient service. A disease is considered to be ‘rare’ when it affects fewer than 1 in every 2,000 inhabitants, has a high mortality rate and/or is chronically debilitating. The low or very low prevalence of rare diseases requires a particular concentration of resources and knowledge. The expertise, therefore, needs to be concentrated into different reference units. These have been grouped into thematic clusters and areas, taking into account the Rare Disease groups established by EURORDIS. The classification of Unit of Clinical Expertise (UEC) is based on an evaluation of the following criteria: Knowledge and experience Multi-disciplinary team Functional plan of the UEC Transition protocol in paediatric UECs List of XUEC accreditations Adult and child Immune diseases: area of primary immunodeficiencies Immune diseases: area of autoinflammatory diseases Immune diseases: area of systemic autoimmune diseases Minority diseases with epilepsy Minority diseases in hemophilia and congenital coagulopathies Minority Endocrine Disorders Non-Oncological Minority Hematological Disorders Hereditary metabolic diseases Neuromuscular diseases Kidney disease Respiratory minority diseases Pediatric Genetically based behavioral cognitive disorders in pediatric age