They may be called rare diseases, but collectively, they afflict nearly one in ten Americans. That’s because there are over 7,000 different conditions that each affect fewer than one-tenth of one percent of people in the United States. For those people, however, the rarity of the disease can make a serious problem into an intractable one. The rarity of these conditions makes it difficult to find treatments or cures.
Most rare diseases are largely or entirely genetic; 80 percent have been traced to genetic causes. Infectious diseases seldom restrict themselves to a small population, and conditions caused by environmental factors pop up as often as people are exposed to those causes, however, some diseases are rare in the United States because they are caused by a microbe or allergen or environmental source not normally found in this country. The diseases themselves resist treatment, but all the more so because the small number of patients makes information scarce, meaning these conditions are difficult for medical researchers to study—and illnesses that affect only a few people are often a low research priority.
Many rare diseases are hard to detect, because they share symptoms with more common conditions, and diagnostic procedures lead doctors to those first. In addition, because so little is known about them, symptoms are easy to miss or misinterpret. All illnesses have more and less common symptoms, but when the disease itself is rare, doctors may not see the rarest symptoms more than once or twice in a generation. In fact, there are diseases with only one or two known cases in recent decades, and it is obviously impossible to tell whether the symptoms those patients display would qualify as “typical” if the illness were more common.
The good news is that more and more research is being done on rare diseases. Public opinion is increasingly focused on gaps and deficiencies in healthcare, so doctors are more motivated to look for ways to deal with even diseases that affect few people. Moreover, government policy is moving towards treating these conditions, and inducements are being created to look into them.