What are Rare Diseases?

How rare is rare?

In the United States, the Food and Drug Administration (FDA) defines a rare disease as any disease that affects fewer than 200,000 Americans. In Europe, a disease is defined as rare when it affects less than 1 in 2,000 people. While these numbers may seem small, consider that there are more than 7,000 known rare diseases which affect around 25 million people. That is roughly 10% of the U.S. population. It is further estimated that 350 million people suffer from rare diseases worldwide.

Rare diseases are an important cause of chronic illness, disability, and premature death in both children and adults. They take a disproportionate share of our health care dollars because of their complexity and the expense of, in most cases, inadequate therapy.

Many fundamental advances in medicine have come from the study of rare diseases and have benefited common diseases. As an example, the study of the human genome began with identification of rare diseases (muscular dystrophy being the first) and epigenetics was first identified in rare disorders. Both because of currently inadequate therapy and the potential to assist common as well as rare disorders, the conduct of clinical research in rare diseases is essential.

The exact cause of many rare diseases is still unknown, but genetics is thought to be a factor for a majority of these diseases. This means that the cause may be traced back to mutations (changes) in a gene. In some cases, these genetic mutations are passed from one generation to the next. It is possible for a rare disease to be present from birth, even though symptoms may not immediately appear. In cases where the rare disease is not inherited, environmental factors may directly or indirectly have a role.

Consider joining a patient organization (patient advocacy group). Patient organizations provide support, resources, and services for patients and families, and actively participate in disease research groups. Also consider joining the RDCRN Contact Registry, which collects and stores the contact information of people who want to participate in RDCRN-sponsored research or learn more about our research. It connects patients with researchers in order to advance rare diseases research.

We also encourage you to share our website with others who have rare diseases and may be interested in our research. With your help, we can learn more about rare diseases and potential treatment options. Help us grow by following us on Facebook, Twitter, LinkedIn, and YouTube. You can also check out our podcast to hear plain language summaries of our latest research.