What is a Rare Disease?


A rare disease is a condition which affects 200,000 or less individuals in the United States. Congress created this definition as part of the Orphan Drug Act of 1983. Rare diseases are often referred to as orphan diseases, as pharmaceutical companies are not interested in pursuing research into their treatments. The Orphan Drug Act created an incentive for pharmaceutical companies to do such research and as such required a definition of a rare disease. The definition of a rare disease does change depending on the part of the world. For example, in the European Union, a rare disease is considered any condition that affects 1 in 2,000 individuals.

There are estimated to be approximately 6,000 - 7,000 different conditions and disorders that meet the definition of a rare disease. These conditions can be difficult to treat as they often have symptoms in common with “regular” diseases. This leads to misdiagnosis and delays in treatment. Even when an individual is finally correctly diagnosed, frustration can occur as there may not even been a treatment available.

The causes for rare diseases are numerous. Genetics seems to be a causal factor in many of the diseases.. The genetic cause can, in some cases, be passed down through the generations. Other possible causes for rare diseases include: rare cancers, infections, and non-inherited autoimmune diseases. The exact cause of many rare diseases is still unknown.

Many rare diseases have a chronic pain component. Examples of some rare disorders that involve chronic pain include, but are not limited to, are: Adult-onset Still's disease, Behçet disease, Charcot-Marie-Tooth disease, Ehlers-Danlos syndromes, neurofibromatosis type 1, palindromic rheumatism, primary biliary cholangitis, and sickle cell anemia.

Doctors are often told the saying “When you hear hoofbeats think horses not zebras”. This means when treating a person, think of the most common disorders, not rare disorders. As a result, many individuals in the rare disease community refer to themselves as “Zebras”.

Rare Disease Day is celebrated on the last day of February.

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