Welcome to the official rare disease educational website developed by The National Organization for Rare Disorders. By raising awareness of rare diseases among physicians, clinicians and other medical professionals, NORD strives to help patients obtain earlier diagnosis and appropriate treatment. Learn more >
A rare disease is one that affects fewer than 200,000 Americans at any given time.
According to the National Institutes of Health, there are between 6,000 and 7,000 rare diseases affecting from 25 to 30 million Americans.
Approximately 50% of the people affected by rare diseases are children.
Since 1983, more than 2,200 rare disease treatments have entered the research pipeline and more than 360 have been approved for marketing.
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+ Amyloidosis
+ Hereditary Angioedema
+ Homocystinurias
+ Treacher Collins Syndrome
+ Tyrosinemia Type 1
+ Urea Cycle Disorders
For additional information on over
3,000 other rare diseases visit
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Overview: The urea cycle disorders (UCD) result from defects in the metabolism of the extra nitrogen produced by the breakdown of protein and other nitrogen-containing molecules.
Author: Marshall L. Summar, M.D.
Chief, Division of Genetics & Metabolism
Children's National Medical Center
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