It is easy to think that you have never known someone with a rare disease because you have never heard of Amyloidosis, Niemann-Pick Type C or Periodic Fever Syndrome (PFS). However, a disease is classified as "rare" if it affects fewer than 200,000 Americans. These diseases typically lack financial incentive to make and market new treatments even though 25 million Americans are diagnosed with one of over 6,000 rare diseases. What's more surprising is that you probably have heard of some of them - cystic fibrosis, leukemia, non-hodgkins lymphoma or even ALS - you just didn't realize they were "rare."

The National institutes of Health database lets you look up diseases that have affected your friends and family:

• Genetic and Rare Diseases Information Center

• Wikipedia: Rare Diseases
• National Organization for Rare Disorders
• About.com: Rare Diseases
• Office of Orphan Products Development (OOPD)
• Rare Diseases Clinical Research Network