The European Union defines a rare disease as as any disease affecting five or fewer individuals per 10,000—and most are due to nothing more than a mutation in a single gene. That may not seem like much, but if you are one of the individuals or families unfortunate enough to be genetically pre-marked for cystic fibrosis, Huntington's disease, or one of the muscular dystrophies, just to name a few, such diseases are very real and very often devastating.

The devastation comes from the fact that as these diseases are "rare"—and since many have symptoms that vary from patient to patient—they're hard to diagnose. These diseases often don't receive as much attention as more common diseases, and it is frequently patients themselves (or the patient's families, as many rare diseases affect children) who initiate the research by reaching out worldwide to find others who are seemingly affected by the disease. Building support networks and creating online resources and communities—as well as databases of affected individuals that clinicians and scientists can tap into—are necessary steps for advancing the basic biology of individual rare diseases and developing treatment strategies.

The stories of these individuals and families are touching and inspiring. Sometimes it's the parents who dedicate their lives to looking first for the correct diagnosis, then for possible treatment options (see one parent's quest to find answers to a son's illness). Sometimes it's partners who seek to outpace the progress of a fatal genetic disease that they know is in one of their loved one's genomes (see one couple's quest to find the cure for a fatal disease). Sometimes it is a researcher studying one aspect of science who decides to shift gears when her offspring is diagnosed with a rare disease (see a scientist's decision to change her research focus).

All of these examples highlight the need to recognize the special burden that rare diseases impose and develop strategies to combat them. Today we mark the tenth annual Rare Disease Day. The goal of this day is to raise awareness about rare diseases not only among the public but also with policymakers who control research funding.

We've made progress over the years. For example, in 1983 the Orphan Drug Act was signed into law by President Ronald Reagan, giving drug companies incentives to develop treatments for these diseases. And thus far more than 450 rare diseases benefit from a marketed drug either in the U.S. or in Europe. Additionally, the National Institutes of Health created an integrated pipeline, the Therapeutics for Rare and Neglected Diseases program, to help speed the development of new treatments for these disorders, as well as the Undiagnosed Diseases Program, and there are currently efforts to explore available oncology drugs for rare disease treatment, as well as basic science efforts to take advantage of technological advances, such as omics techniques, to better understand diseases such as ALS (see here).

Although progress has been made to identify the genetic etiology of these diseases, particularly through whole genome and exome sequencing, knowledge of how mutations in these genes affect the disease is still lacking, as funding is often scarce for research on conditions with such a small market. A lack of existing literature and investigators working on the same disease poses additional barriers.

However, scientists should not be discouraged from investigating rare diseases, as most discoveries that stem from basic research into them will likely help us to better understand human physiology and more common and complex conditions. On that note, I was happy to see the U.S. National Institutes of Health and numerous other communities worldwide (check here for your local event) dedicate efforts to talk about rare diseases, the people affected by them, and the scientists and clinicians who dedicated to tackling them. It is through the collaboration of basic researchers, clinicians, patient families, and awareness days such as National Rare Disease Day that insights into these rare diseases have come to light—but much still remains to be done.