Source:http://linkedlifedata.com/resource/umls/id/C0678236
MEDLINEPLUS: <p>A disease is rare if fewer than 200,000 people in the United States have it. There are close to 7,000 rare diseases and about 25 million people in the U.S. have one. Many rare diseases are caused by changes in genes and are called <a href='http://www.nlm.nih.gov/medlineplus/geneticdisorders.html'>genetic diseases</a>.</p><p style="font-weight:bold;font-style:italic;">NIH: National Institutes of Health Office of Rare Diseases</p>,MSH: A large group of diseases which are characterized by a low prevalence in the population. They frequently are associated with problems in diagnosis and treatment.,NCI: A non-malignant disease that affects fewer than 200,000 people in the United States. (from National Organization for Rare Disorders)