What is an Undiagnosed Disease

Is your patient undiagnosed?

What is an undiagnosed disease?

An undiagnosed disease is a medical condition without a known cause, even after many tests and visits to different specialists. About 30 million people in the U.S. live with a rare disease. A portion of those people live with an undiagnosed condition. Researchers estimate about 80% of undiagnosed diseases have a genetic cause.

Why are some diseases difficult to diagnose?

A condition can be hard to diagnose if:

  • It is a rare disease. Ultra-rare diseases that affect fewer than 1 in 50,000 people are especially difficult to diagnose since most doctors are unfamiliar with them. 
  • Symptoms are atypical of a known condition. 
  • The disease hasn’t been discovered or published in medical literature.  
  • Patients can’t get the right tests or travel to see rare disease specialists. Barriers for patients can include insurance, financial, and health issues. 

What are the symptoms of an undiagnosed disease?

About 40% of UDN applicants have neurologic symptoms, making these the most common symptoms of UDN patients. Other symptoms can affect any body system, such as the immune system, heart or vascular system, or gastrointestinal tract. 

Patients often have multiple symptoms with no diagnosis or multiple diagnoses from different specialists. They often hear doctors say that they or their child is a medical mystery. 

Living with an undiagnosed condition

Not knowing the cause of serious health issues can cause physical, emotional, and financial stress. Patients and their families may have fear for the future and feel alone without a support group or disease organization to turn to for help. 

Hope for the future 

At the UDNF, we bring hope to people with undiagnosed diseases.

We have a community where you can connect with others living with an unexplained illness and get helpful resources. 

Our Patient Navigation Program guides patients and families through the UDN program. Our Patient Navigators also provide support and resources for undiagnosed and ultra-rare disease patients.  

We fund research to find treatments for ultra-rare diseases. 

We work to increase support and funding for the UDN program and advocate for legislative changes that benefit the undiagnosed and ultra-rare community.


Undiagnosed Disease Network Quarterly Report Spring 2024 


Walley, N. M., Pena, L. D. M., Hooper, S. R., Cope, H., Jiang, Y. H., McConkie-Rosell, A., Sanders, C., Schoch, K., Spillmann, R. C., Strong, K., McCray, A. T., Mazur, P., Esteves, C., LeBlanc, K., Undiagnosed Diseases Network, Wise, A. L., & Shashi, V. (2018). Characteristics of undiagnosed diseases network applicants: implications for referring providers. BMC health services research, 18(1), 652. https://doi.org/10.1186/s12913-018-3458-2