What Are Rare Diseases?


Rare Disease Day is observed on February 28, the rarest date of the year. The rare disease movement is a global effort developed to ensure that people with rare diseases are supported and have access to diagnosis, treatments, healthcare services, and other specialized resources. Established in 2008, Rare Disease Day has been instrumental in creating a global, multi-disease, diverse community for people with rare diseases.

Many people with rare diseases experience a sense of isolation and may perceive the future as dismal and difficult.8 Even though rare diseases are considered rare, about 30 million people in the United States, or 1 in 10 people, suffer from one of the 7,000+ known rare diseases.3

“Individually, these different diseases are rare; but combined, they affect many different people,” said Carli Andrews, MS, CGC, Medical Science Liaison at Baylor Genetics. “Addressing [rare diseases] with a group approach allows for better advocacy for treatments and research that show the overall progression of a disease. Community can be important when someone is diagnosed with a rare disorder.”

Understanding your patient’s unique disease symptoms, diagnosis, and available treatments can be challenging. However, with the power of community, advocacy, and research, we have the potential to detect, treat, and eventually cure diseases that may have been misunderstood. We can create a brighter future for those living with rare diseases by coming together and creating a strong network of support.

Searching for answers to rare complex symptoms can be stressful for the patient and the provider. We have been supporting healthcare providers with our comprehensive genetic tests for more than a decade, which has aided in diagnosis, further research, and better medical management. At Baylor Genetics, our goal for Rare Disease Day (and beyond) is to spread awareness and support the community with our comprehensive genetic tests.


Rare diseases are often misdiagnosed or remain undiagnosed for lengthy periods of time. This is often due to symptoms not always being obvious or healthcare providers having little to no clinical experience with a particular disease. Similar clinical difficulties are present in all rare diseases and as a result, diagnoses are frequently delayed or inaccurate.

Another dilemma when it comes to finding appropriate care and treatment options for your patient is that rare diseases are mandated differently across the world. Currently, there are no globally defined criteria for what a rare disease is. The eligibility requirements are made by drug regulatory agencies in each country across the globe.

For the United States, the 1983 Orphan Drug Act defines a rare disease as a condition affecting fewer than 200,000 people.1 In contrast, the European Union follows the Orphan Regulation. Introduced in 2000, the regulation defines a disease as rare “when it affects less than 1 in 2,000 people.”1

Although the definition of a rare disease differs from country to country, genetic testing can help influence these laws by providing further insight into these diseases and how they are managed. Genomic sequencing may be the solution for many healthcare providers and their patients.

At Baylor Genetics, we offer comprehensive genetic testing, such as Whole Exome and Whole Genome Sequencing (WES/WGS), which have been proven to be an effective method for diagnoses. Currently, we have a partnership with Undiagnosed Diseases Network (UDN), which is backed by the National Institutes of Health Common Fund. Through this partnership, Baylor Genetics performs sequencing services for exome and genome to help the UDN solve the “most challenging medical mysteries.”

Rare diseases are constantly evolving based on demographics. This includes age, race, ethnicity, and gender, as well as environmental factors, such as the use of drugs, alcohol, diet, or exposure to chemicals. All these aspects can influence rare diseases, and some may even arise spontaneously.

Since rare diseases occur in many ways, you may be curious to know which genetic tests can identify these diseases.


Identifying and detecting rare diseases through genetic testing can be life changing for some patients. Genetic testing can bridge the gap between past, present, and future generations, and give hope to those who have inherited a rare disease. At Baylor Genetics, we offer several sequencing tests and microarrays that can help identify and detect rare diseases.

  • Whole Genome Sequencing (WGS): WGS provides the most comprehensive overview of our genetic information. In a single test, it examines up to 98% of the human genome and holds the power to provide answers to complex conditions your patient may be dealing with.
    • Benefits: Benefits of WGS include its ability to identify most genetic variants. Our WGS covers single nucleotide variants, structural variants, copy number variants (CNV), mitochondria genome variants, and short tandem repeats in coding and non-coding regions.
    • Limitations: Limitations of WGS include a higher cost, when compared to other genetic testing methods.
  • Whole Exome Sequencing (WES): WES is an essential tool for gathering a better understanding of your patient’s exome, which contains the protein-coding regions of DNA. While the exome only makes up about 1-2% of the genome, it is estimated to contain about 85% of disease-causing mutations.
    • Benefits: Benefits of WES include the ability to analyze a patient’s entire set of protein-coding genes in one test.
    • Limitations: Limitations of WES include the lack of coverage for repeat expansions, mitochondrial DNA variants, and CNV analysis.
  • Mitochondrial DNA testing (mtDNA): MtDNA testing analyses changes in hundreds of genes found to be associated with mitochondrial disorders. Mitochondrial disorders often impact multiple organ systems, such as muscles, eyes, brain, or liver. These disorders, ranging from mild to severe, can be identified at any point during a patient’s life.
    • Benefits: Benefits of mtDNA testing include the ability to identify disease-causing mutations in the mitochondrial genome. Our test measures targeted nuclear heteroplasmy down to 1.5% and detects large deletions/duplications.
    • Limitations: Limitations of mtDNA testing include lack of coverage of nuclear gene variants. While this assay can detect large deletions and multiple deletions but does not provide an accurate determination of the heteroplasmy level of such rearrangements due to preferential amplification of the smaller molecules.
  • Chromosomal Microarray Analysis (CMA): CMA provides comprehensive genetic testing for the most common chromosomal abnormalities, including deletions and duplications. These extra or missing chromosomal segments may cause a genetic disease that results in significant disabilities. CMA can detect more chromosomal abnormalities than traditional chromosome analysis (karyotype).
    • Benefits: Benefits of CMA include maximum sensitivity for detection of copy number changes and a higher diagnostic rate than traditional cytogenetic tests.
    • Limitations: Limitations of CMA include the inability to detect small copy number variants under the resolution of the array or single nucleotide changes.
  • Global Metabolomic Assisted Pathway Screening (Global MAPS®): Global MAPS® is a metabolic profiling test aiming to diagnose Inborn Errors of Metabolism (IEM). Global MAPS analyzes disruptions in individual analytes and pathways related to biochemical abnormalities
    • Benefits: Benefits of Global MAPS® include the ability to identify over 700 metabolites in human plasma and urine that would usually require many different tests. This test defines biochemical pathway errors not currently detected by routine clinical or genetic testing.
    • Limitations: Limitations of Global MAPS® include the inability to identify any large peptides, proteins, complex oligosaccharides, large lipids, and elements.

Genetic testing gives hope for patients with rare diseases, which can have devastating and life-altering effects. It may lead to more precise diagnoses, more effective medications, and important information about the underlying causes of a person’s ailment. If you are interested in pursuing genetic testing for one of your patients, our genetic counselors are here to help for further consultation.

Through genetic testing, patients living with a rare disease can acquire the tools they need to manage their health and lead longer and more fulfilling lives.


Rare diseases are unique. Each disease requires tailored treatment specific to the symptoms and conditions of each patient. Treatments for rare diseases are commonly focused on symptom management or to enhance a patient’s quality of life.

Some treatment options include:

  • Medications
  • Surgical procedures
  • Physical therapy

Furthermore, clinical trials can help examine new potential therapies or treatments which may positively impact the lives of rare disease patients. Before choosing a treatment for your patient, it should be carefully evaluated and tailored to their health needs.

“Unfortunately, for many rare diseases, there is no treatment,” said Andrews. “But for some genetic conditions, specifically metabolic conditions, there are treatments and/or medical management changes that can drastically improve and prevent symptoms.”

One treatable rare disease is biotinidase deficiency, which prevents the body from processing the vitamin biotin. Biotin is responsible for properly metabolizing lipids, carbohydrates, and the amino acids that make proteins.9 The treatment for this condition is to take biotin every day.

Due to the unique nature of rare diseases, further research must be conducted to learn more about which treatment options may be best for your patient. Even with a large population of individuals affected, there is still no cure for more than 90% of rare diseases.2

According to the Food and Drug Administration, “some rare disease treatments have been ‘orphaned’ or discontinued because there was not enough financial incentive to continue development or production.”4

Advocacy is essential to ensure patients get the treatments they need to live comfortably. Through advocacy, we can increase funding to support research and the development of new treatments. In addition, awareness and the promotion of research is imperative to create better medical management for rare disease patients.


The Rare Disease Day organization, established by the European Organization for Rare Diseases, and more than 65 national alliance patient organization partners “provides an energy and focal point that enables rare diseases advocacy work to progress on the local, national, and international levels.”6

Rare Disease Day has helped 300 million people globally, including patients and their families, by providing resources to further assist them on their healthcare journey.6 The National Organization for Rare Disorders (NORD) and Rare Diseases Clinical Research Organization (RDCRN) have also devoted their resources to help those who are experiencing a rare disease.

NORD is the largest, rare disease organization and charity in the United States. All 7,000+ rare diseases are the focus of NORD’s commitment to their diagnosis, treatment, and cure.7 NORD offers programs for rare disease advocacy, education, research, and patient and family care to better educate and promote patient care.

The RDCRN initiative supports clinical studies and promotes collaboration and advocacy to enhance research studies on rare diseases. According to the RDCRN, their “consortia, physician scientists and multidisciplinary teams work together with patient advocacy groups to study more than 200 rare diseases at sites across the nation.”5

Additionally, there are many disease-specific organizations that have made significant progress in clinical trials, treatment, and care for rare disease patients. Some of these rare disease organizations include:

These organizations provide advocacy, support, and resources to those affected by rare diseases, often when no other options exist. By coming together, they provide a sense of community for those living with a rare disease.


Through our comprehensive testing Baylor Genetics can help provide a diagnosis for those with undetermined phenotypes, find new treatments, and improve the quality of life for patients suffering from rare diseases.

By collaborating with the healthcare community and rare disease organizations, we can increase our understanding of these complex diseases to support and treat those affected. Furthermore, by coming together, we can better understand our health and the health of future generations.

Baylor Genetics supports providers and their patients who have been impacted by a rare disease. Our comprehensive and targeted testing approaches are here to help find the answers you need to acquire and promote adequate medical management and treatment for your patients.

Together, we can make a difference.


  1. Haendel, M., Vasilevsky, N., Unni, D., Bologa, C., Harris, N., Rehm, H., Hamosh, A., Baynam, G., Groza, T., McMurry, J., Dawkins, H., Rath, A., Thaxon, C., Bocci, G., Joachimiak, M. P., Köhler, S., Robinson, P. N., Mungall, C., & Oprea, T. I. (2020). How many rare diseases are there?. Nature reviews. Drug discovery, 19(2), 77–78. https://doi.org/10.1038/d41573-019-00180-y
  2. Kaufmann, P., Pariser, A.R. & Austin, C. From scientific discovery to treatments for rare diseases – the view from the National Center for Advancing Translational Sciences – Office of Rare Diseases Research. Orphanet J Rare Dis 13, 196 (2018). https://doi.org/10.1186/s13023-018-0936-x
  3. National Institutes of Health. Genetic and Rare Diseases Information Center. (2023. February). https://rarediseases.info.nih.gov/about
  4. Rare Diseases at FDA. U.S. Food & Drug Administration. (2023, February). https://www.fda.gov/patients/rare-diseases-fda
  5. National Center for Advancing Translational Sciences. Rare Diseases Clinical Research Network. (2023, February). https://ncats.nih.gov/rdcrn
  6. Rare Disease Day. What is Rare Disease Day? (2023, February). https://www.rarediseaseday.org/what-is-rare-disease-day/
  7. National Organization for Rare Disorders. Rare Diseases Database. (2023, February). https://rarediseases.org/rare-diseases/
  8. von der Lippe, C., Diesen, P. S., & Feragen, K. B. (2017). Living with a rare disorder: a systematic review of the qualitative literature. Molecular genetics & genomic medicine, 5(6), 758–773. https://doi.org/10.1002/mgg3.315
  9. Mount Sinai. Vitamin H (Biotin). (2023, February). https://www.mountsinai.org/health-library/supplement/vitamin-h-biotin#:~:text=Your%20body%20needs%20biotin%20to,body%20does%20not%20store%20it

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