Rare Disease Overview
The precise definition of a rare disease is a matter of some debate between nations, but a prevalence of 40 cases per 100,000 or less is the global average. Orphan diseases are disorders that do not yet have a treatment, often (though not always) simply because their rarity makes it economically unviable to do the necessary research; a drug developed for an orphan disease despite the potential loss is known as an orphan drug. As so few rare diseases have viable, tested treatments as yet, most grouping schemes focus on the body system affected by the disease.
Note that due to the nature of this request, the necessity of referencing government and academic resources which have long publication cycles and which are often slow to update, we have not restricted ourselves to sources published in the last two years per our standard procedure. In all cases in which an older source is cited, we have used sources like Google's Scholar database to check for more recent research.
- The US Centers for Disease Control (CDC) defines a rare disease as a condition that affects fewer than 200,000 people worldwide.
- However, this is not a universal definition. Most regions and countries define rare diseases by prevalence rather than total incidence, ranging from 5 to 76 cases per 100,000, with a global average of 40 cases per 100,000.
- Qualifiers for a rare disease other than prevalence are rare (<30%) in formal definitions among health organizations worldwide; where they do exist, qualifiers most often relate to the severity of the disease and/or the lack of existing treatments.
- For example, RareDiseaseDay.org describes rare diseases as, "Quintessentially disabling, the patient's quality of life is affected by the lack or loss of autonomy due to the chronic, progressive, degenerative, and frequently life-threatening aspects of the disease."
- While "rare disease" is the most common term used internationally, other terms include rare condition, rare disorder, rare and neglected disease (overlapping with orphan disease), very rare disease, syndrome without a name, etc.
- The lack of a universal terminology or definition has been noted by organizations like the ISPOR Rare Disease Special Interest Group, sparking an international effort to develop a unified standard; thus far, the Group has focused on understanding how different regions and nations define rare disease and has not yet provided recommendations for a global standard.
- While not formally defined by the CDC, an orphan disease is one that the pharmaceutical industry has not researched or developed a treatment for "because it provides little financial incentive for the private sector to make and market new medications."
- This is despite the Orphan Drug Act of 1983 attempting to provide additional incentive by offering a seven-year exclusive market to companies who develop drugs to treat rare diseases.
- As of 2018, about 95% of the 7,000 known rare diseases still lack any treatment options.
- While an orphan disease may be a rare disease, it can also be a more common disease, such as cholera, malaria, tuberculosis, or typhoid, which has been ignored due to being far more prevalent in the developing world than in developed countries.
- There is no universally accepted system for categorizing rare diseases, though organizations like ISPOR are making efforts to correct this.
- Most rare diseases (72%, over 7,000 identified so far) are genetic or congenital in origin.
- Notably, despite this, only 5% of drug and biologic rare disease treatments approved by the FDA in 2017 targeted genetic rare diseases.
- The FDA divides rare disease treatments (and, therefore, the diseases themselves) into the following categories:
- Similarly, the NIH rare diseases page categorizes diseases by the bodily system they impact but has expanded that list to 32 total categories.
- The 20 consortia under the International Rare Diseases Research Consortium (IRDiRC) are designated by a combination of body systems and disease types, though this is far from a formal classification system.
- Orphanet, likewise, suggests 21 disease categories based on a combination of body system and disease presentation.
- The reason that rare diseases tend to be grouped by body system rather than treatment type is that so few have viable treatments as yet.
- Under the CDC's definition, rare diseases collectively affect 25 million people in the US and 300 million to 400 million worldwide. Another estimate holds that 3.5% to 5.9% of the worldwide population suffers from a rare disease.
- Under European definitions, about 30 million people (1 in 17) suffer from a debilitating rare disease.
- 70% of rare diseases begin in childhood (unsurprising, given that 72% are genetic in origin), and overall, 50% of rare diseases impact children, with 30% dying within 5 years.
- We find no evidence that rare diseases affect one gender more than another, though we suspect that many individual rare diseases would affect one over the other.
- Top disease categories which require caregiving can be seen in slide 9 of the project slideshow.
- Useful charts and graphs for this report (including the other briefs in this series) can be found here, with source citations at the bottom of each slide.