Below is an overview of rare genetic disease, and the subset within rare disease of undiagnosed disease. This overview includes some key terms and processes including genetic testing and resources for those seeking more information or access to genetic testing. The GREGoR Consortium does not provide clinical advice or genetic testing - this information is offered as a resource to patients and families.
Frequently Asked Questions (FAQs)
What does it mean for a health condition to be genetic?
What does ‘Mendelian’ mean?
What is a rare genetic disease?
A rare genetic disease is defined as a condition that impacts fewer than 200,000 people in the U.S. There are more than 10,000 known rare diseases that affect about 1 in 10 people (or 30 million people) in the U.S. Other countries may have their own official definitions of a rare disease. For example, the European Union defines a disease as rare when it affects fewer than 1 in 2,000 people.
What is the difference between ‘familial’ and ‘sporadic’ rare genetic disease? What is meant by ‘rare’ versus ‘undiagnosed’ disease?
What is meant by the 'diagnostic odyssey'? What if there is no diagnosis?
There are a few options if a diagnosis cannot be made. Re-analysis of genetic data every few years is one way to re-evaluate a genetic test. New clinical genetic tests may become available as new technologies are developed over time. Individuals can also enroll in research studies in which researchers plan to return results to participants and are using and developing research tests that are not yet be available in a typical medical setting. Patients can enquire with their medical and insurance providers about whether some or all of these options are available to them.
What is involved in genetic testing in a clinic?
Genetic testing is the use of a clinical test to examine an individual’s DNA. There are many types of genetic tests including tests designed to look for large changes impacting many genes, as well as genetic tests designed to detect small changes or variations within genes.
In a medical setting, the results of a genetic test can be used to confirm or rule out a suspected genetic disease. Results may also be used to determine the likelihood of parents passing on a genetic mutation to their children - in this case, the parents of the affected individual or those considering having children are tested. For a child, genetic testing can be performed prenatally or after birth.
Results from genetic testing are often not black and white for rare genetic diseases. For some, a genetic test result may find a genetic variant that is the cause of a genetic condition (a pathogenic or “positive” result). For others, it may not find any genetic variants that explain the symptoms (a benign or “negative” result). Testing can also find a genetic variant for which we do not yet know if or how this variant may impact health (variant of uncertain significance or VUS). Genetic testing can also reveal information that is unexpected or unrelated to the initial purpose for doing the genetic test (sometimes called “incidental” or “secondary” findings).
What are some resources to learn more about rare or undiagnosed diseases, or to enquire about genetic testing?
The GREGoR Consortium does not provide clinical advice, clinical genetic testing, or direct support to patients. If you or a family member or someone you care for has a rare disease, there are local, national, and international resources that may be helpful. Some of these include:
- Genetic Alliance
- Genetic and Rare Disease Information Center
- Global Genes
- MedlinePlus Genetics - Help Me Understand Genetics page
- National Organization for Rare Disorders
- Rare Disease Day
- Undiagnosed Diseases Network
- Undiagnosed Diseases Network Foundation
For more information about how to get clinical genetic testing or to have an evaluation by a genetics professional, you can speak with your healthcare provider or find a clinic in your area: