Top 5 Reasons to Study Rare and Undiagnosed Diseases

Monday, June 1, 2015

What is a rare disease? And how rare is “rare”? When I began my research at the NIH, I had a textbook understanding of rare diseases, but now, after four years as a postdoc in the IRP, I understand a bit more of what it means to the patients and researchers who try to help them.

Approximately one in 10 Americans has a rare disease.

A disease is classified as rare when it affects less than 200,000 people in the United States. There are more than 6,800 known rare diseases. Although each one affects a relatively small number of people, an estimated 25 to 30 million Americans—roughly 10 percent of the population—live with a rare disease. While some of these people have a diagnosis, many do not.

In 2008, the NIH established the Undiagnosed Diseases Program to help find a diagnosis for people with mysterious and extremely rare medical conditions. Sometimes people ask why, with limited research funding available, biomedical scientists are studying rare and undiagnosed diseases that affect a few people rather than investigating only common diseases that affect many. So, here are my top five reasons (in no particular order):

1. Investigating the underlying mechanism for rare and undiagnosed diseases can yield some of the most interesting scientific discoveries.

Examining how and why a gene isn’t working properly in a disease can help us discover the gene’s normal function. Because many rare and undiagnosed diseases have been studied much less than more common diseases, the genes involved in the former are often poorly characterized. As a result, any discoveries that are made about these genes and diseases are often new and exciting.

2. Rare diseases are often caused by a mutation in one gene, which makes proving that it is the cause of the disease much simpler.

In contrast to rare diseases, common diseases like diabetes, obesity, and many forms of cancer are rarely caused by only one genetic mutation—they usually arise from a combination of many genetic and environmental factors. This makes determining the cause of common diseases a bit more complicated. For example, if a car is missing its engine, you can immediately see that the engine is required to produce the energy to move the car along the street. However, if a car is missing its wheels, engine, and steering wheel, it is more difficult to determine the function of each missing part.

3. Studying the role of a gene in a rare or undiagnosed disease can help our understanding of related common diseases.

Genes and the proteins that they encode interact and affect one another. Discovering the gene involved in a rare disease and its function can shine light on the function of other gene products that interact with it. In this way, research on rare disease genes can also impact our understanding of other diseases, including common ones.

4. There is less competition.

Because rare and undiagnosed diseases are studied much less than common diseases, scientists who choose to study them do not have as many competitors trying to publish before them. Scientists who investigate common diseases usually have many competitors and can spend years generating data that is unable to be published because someone else beat them to it.

5. People with rare and undiagnosed diseases need help too! 

While there may be fewer of them, patients with rare and undiagnosed diseases need just as much (if not more) help. These patients often have more serious clinical presentations and fewer treatment options available.

These are the reasons that I came up with, but there are probably many more. Do you have more ideas for why researchers should investigate rare and undiagnosed diseases?

To learn more about the different research programs for rare diseases at the NIH, visit:

And to learn more about the Undiagnosed Diseases Program, visit: