What are Ultra-Rare Diseases

Is Your Patient Undiagnosed?

What are ultra-rare diseases?

An Ultra-rare disease is a condition that affects fewer than 1 in 50,000 people. This means that in the U.S., for any ultra-rare disease, less than 7000 people live with that condition. Some of these diseases are so rare that only a few people in the world have it.

Causes of ultra-rare disease

Genetic factors cause most ultra-rare diseases. A 2022 study published in the Orphanet Journal of Rare Diseases showed that most ultra-rare disorders are due to a change in just one gene. These changes can be from a dominant or recessive inheritance. The rarer the disease, the more likely a recessive gene change caused it. 

Getting an ultra-rare diagnosis

The journey to a rare disease diagnosis is often long, difficult, and expensive. Patients may see dozens of doctors and undergo many tests before they finally get a diagnosis. 

When they finally get a diagnosis, they might feel mixed emotions. They may feel relief that they have an answer, but also confusion, sadness, and fear because there is not any treatment or support groups due to the rarity of the disease.

Challenges faced by patients with ultra-rare diseases

Lack of research and treatments: Often, no treatments are available for ultra-rare diseases. Research is limited because so few people can participate in studies. 

Lack of community and patient organizations: There may not be any support groups or organizations for an ultra-rare disease. This makes it hard for patients and their families to find help and resources.

How the UDNF helps ultra-rare disease patients

Community: We have a community for people with undiagnosed and ultra-rare diseases. You can meet others who understand what you’re going through and find resources to help.

UDN Patient Support: Our Patient Navigation Program helps patients interested in applying to or already in the UDN program. Our Patient Navigators also provide support and resources to undiagnosed and ultra-rare patients.

Research Funding: We fund research to help diagnose and treat ultra-rare diseases. The UDNF Therapeutic Matching Program aims to identify treatments for rare disease patients.

Advocacy: We advocate for more support and funding for the UDN and other legislative initiatives affecting people with undiagnosed and ultra-rare conditions.

9 Signs of a rare disease 

*If you or your patient has two or more of these signs, a referral to a geneticist or the Undiagnosed Diseases Network (UDN) may be warranted.*

  1. Physical Features: Distinctive facial features, skeletal differences, or organ malformations.
  2. Developmental Delays: Delays in achieving milestones or a sudden loss of milestones such as language, motor, or social skills. 
  3. Intellectual Disability: Cognitive impairment or learning difficulties. 
  4. Growth Concerns: Failure to thrive or excessive growth 
  5. Recurring Health Issues: Immune system dysregulation, frequent infections, or other recurring symptoms
  6. Sensory Challenges: Hearing loss, vision or eye problems, or other sensory issues. 
  7. Multiple Specialty Visits: Seeing multiple specialists that results in no diagnosis or multiple seemingly unrelated diagnoses. 
  8. Family History: Family history of unexplained health problems, birth defects, or developmental delays. 
  9. Unexplained Symptoms: Symptoms that cannot be explained by common or known conditions.


Frederiksen, S.D., Avramović, V., Maroilley, T. et al. Rare disorders have many faces: in silico characterization of rare disorder spectrum. Orphanet J Rare Dis 17, 76 (2022). https://doi.org/10.1186/s13023-022-02217-9

Harari, S. (2016). Why we should care about ultra-rare disease. European Respiratory Review, 101-103.


Smith, C. I. E., Bergman, P., & Hagey, D. W. (2022). Estimating the number of diseases – the concept of rare, ultra-rare, and hyper-rare. iScience, 25(8), 104698. https://doi.org/10.1016/j.isci.2022.104698