How many rare diseases are there?

February 04, 2020

Some diseases are like black swans. They occur so rarely that many physicians never encounter them in their clinical practice, complicating efforts to treat them.

How many rare diseases are there? According to a new study co-led by University of New Mexico data scientist Tudor Oprea, MD, PhD, no one really knows - and that's a problem, because it's likely that many rare disease patients do not receive appropriate medical care.

In a commentary published in Nature Reviews Drug Discovery, a high-impact research journal, Oprea and colleagues from the U.S., Australia, France and Germany point out that as much as 10 percent of the world's population suffers from a rare disease, which translates into hundreds of millions of people.

"You have thousands and thousands of papers a year related to rare diseases, yet very few translate into cures," says Oprea, professor and chief of the Translational Informatics Division in UNM's Department of Internal Medicine.

A big part of the problem has to do with definitions, the authors argue, because the inability to reliably diagnose a rare disease hinders researchers' ability to develop treatments for it.

In the U.S., the Orphan Drug Act of 1983 defines a rare disease as one affecting fewer than 200,000 people. In the European Union, legislation introduced in 2000 defines it differently: when fewer than one in 2,000 people is affected.

And, the authors point out, a disease that is considered "rare" in the general population might be relatively common within a subgroup - examples include Tay-Sachs disease among Ashkenazi Jews and sickle cell disease among people of sub-Saharan African descent.

Another complicating factor is that the terms used to define diseases are often inconsistent and imprecise, and they sometimes vary from country to country. For example, "breast cancer" actually encompasses a variety of tumor sub-types with unique genetic signatures and different optimal treatments, Oprea says. Should it be classified as one disease or many?

Estimates of the number of rare diseases usually settle in the range of 7,000, the authors report. But their recent analysis of an international disease classification database known as the Monarch Disease Ontology - or Mondo - suggests it could be as much as 50 percent higher.

"The Mondo project is the first computer-assisted human curation process to bring together separate efforts in the rare disease community in order to catalog and annotate all rare diseases, regardless of country or disease type," Oprea says.

Improving care for patients with rare diseases requires reaching consensus on the physical, genetic and environmental characteristics of each condition, but overlapping terminologies and models makes that difficult. The authors are calling upon the World Health Organization, the U.S. Food and Drug Administration, the European Medicines Agency, the National Academy of Medicine and other entities, to adopt a unified definition of rare diseases.

"We encourage the community to get together and come up with more precise rare disease definitions," Oprea says. "There needs to be a forum to discuss this and dedicated funding mechanisms to address it."
-end-


University of New Mexico Health Sciences Center

Related Disease Articles from Brightsurf:

CLCN6 identified as disease gene for a severe form of lysosomal neurodegenerative disease
A mutation in the CLCN6 gene is associated with a novel, particularly severe neurodegenerative disorder.

Cellular pathway of genetic heart disease similar to neurodegenerative disease
Research on a genetic heart disease has uncovered a new and unexpected mechanism for heart failure.

Mechanism linking gum disease to heart disease, other inflammatory conditions discovered
The link between periodontal (gum) disease and other inflammatory conditions such as heart disease and diabetes has long been established, but the mechanism behind that association has, until now, remained a mystery.

Potential link for Alzheimer's disease and common brain disease that mimics its symptoms
A new study by investigators from Brigham and Women's Hospital uncovered a group of closely related genes that may capture molecular links between Alzheimer's disease and Limbic-predominant Age-related TDP-43 Encephalopathy, or LATE, a recently recognized common brain disorder that can mimic Alzheimer's symptoms.

Antioxidant agent may prevent chronic kidney disease and Parkinson's disease
Researchers from Osaka University developed a novel dietary silicon-based antioxidant agent with renoprotective and neuroprotective effects.

Tools used to study human disease reveal coral disease risk factors
In a study published in Scientific Reports, a team of international researchers led by University of Hawai'i (UH) at Mānoa postdoctoral fellow Jamie Caldwell used a statistical technique typically employed in human epidemiology to determine the ecological risk factors affecting the prevalence of two coral diseases--growth anomalies, abnormalities like coral tumors, and white syndromes, infectious diseases similar to flesh eating bacteria.

Disease-aggravating mutation found in a mouse model of neonatal mitochondrial disease
The new mitochondrial DNA (mtDNA) variant drastically speeds up the disease progression in a mouse model of GRACILE syndrome.

Human longevity largest study of its kind shows early detection of disease & disease risks
Human Longevity, Inc. (HLI) announced the publication of a ground-breaking study in the journal Proceedings of the National Academy of Sciences (PNAS).

30-year study identifies need of disease-modifying therapies for maple syrup urine disease
A new study analyzes 30 years of patient data and details the clinical course of 184 individuals with genetically diverse forms of Maple Syrup Urine Disease (MSUD), which is among the most volatile and dangerous inherited metabolic disorders.

Long-dormant disease becomes most dominant foliar disease in New York onion crops
Until recently, Stemphylium leaf blight has been considered a minor foliar disease as it has not done much damage in New York since the early 1990s.

Read More: Disease News and Disease Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.