Rare diseases, by definition, affect a small population. Definitions differ globally; for example, the WHO (World Health Organization), defines a rare disease as one that affects fewer than one in 2000 people, and this is the definition that's used in Europe and the UK. In the US a rare disease is defined as affecting fewer than 200,000 people across the country.
Treating rare diseases has a high cost for healthcare systems. In a 2018 report, the cost of rare disease patients up to the point of a diagnosis to NHS England over ten years was greater than £3.4 billion. [1]
The importance of rare diseases
While rare diseases are rare individually, there are between 6000 and 8000, with new conditions being discovered regularly. They collectively affect around 400 million people worldwide. Around 70% of rare diseases present in childhood, about 80% are caused by single gene mutations, and over 90% of rare diseases do not have approved treatments. On average, it takes over four years to get an accurate diagnosis, and this may include a number of incorrect diagnoses. Some people never get a diagnosis in their lifetime, as the symptoms can be vague or common to other disorders. This extended timescale can have a major impact on patients and their families, by delaying access to any treatment that is available, and to specialist support such as charities and advocacy groups. [2-4]
Some countries carry out newborn screening for rare diseases. For example, NHS England has expanded its newborn screening to include over 200 genetic conditions where there is a treatment available, allowing access to therapy before the disease becomes symptomatic. Under the Generation Study, led by Genomics England, newborn babies are offered whole genome sequencing shortly after birth.
There are arguments that screening should be extended to untreatable conditions, allowing parents or carers to access appropriate support or find other families in similar situations.
The market size
According to a 2024 report, the global rare disease treatment market size was worth around $195.2 billion in 2024, and is anticipated to expand at a CAGR (compound annual growth rate) of 11.6% by 2030. The largest share of the market is in treatments for rare cancers, and the share for musculoskeletal conditions is expected to grow between 2024 and 2030. Biologics make up over half of the market share. [5]
Working in rare diseases: A business model
Developing a drug for a rare disease is risky. The costs of development are as high or higher than creating a drug for a more common disorder, the pool of patients for clinical trials is limited, and the market is small.
Intervention by governments across the world has made it viable for biopharma companies to move into the rare diseases market. As an example, the Orphan Drug Act (ODA) was signed into law in the United States in January 1983. The ODA allowed the establishment of the Orphan Products Grants Program and the Orphan Drug Designation Program, both of which have provided financial incentives for developing drugs for rare diseases, which offset the associated costs and risks. These incentives include tax credits for clinical trials, waiving of FDA (Food and Drug Administration) user fees, development grants, fast-track approval and longer marketing exclusivity (up to seven years) after approval for the orphan-designated indication. [6, 7]
Between 1983 and 2022, under the ODA, 6,340 orphan drug designations were granted, including 1,079 rare diseases. Of these designations, 882 resulted in at least one FDA approval for drugs for 392 rare diseases. Of the top ten designated and approved diseases, seven were rare cancers. [7]
Patient advocacy groups have played a vital role in the development of drugs in rare diseases. The ODA was passed as a result of lobbying by the National Organization for Rare Disorders (NORD). They also provide input into clinical trial design, as the individuals involved understand their disease (or their child's disease) very well, including the progression of the disease and the challenges they face.
Working in rare diseases can provide an understanding of genetic mutati...
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