What are some of the most common rare diseases

Rare diseases aren't as rare as you might think.

In the U.S., the Orphan Drug Act of 1983 defines a disease as "rare" if it affects fewer than 200,000 people. Around one in 10 Americans lives with at least one of more than 7,000 rare diseases.

For providers this results in a difficult scenario: It's quite likely that a small-but-significant portion of your patient base will eventually require care for a disease (or diseases) that your care teams may not have previously encountered or been trained to handle. And while rare disease treatment can present a lucrative reimbursement opportunity for providers, hiring specialists or training your own staff to diagnoses and treat even a limited number of rare diseases represents an expense that may not pay off, especially in the short term.

This concern was reflected in our 2023 rare disease report, built from a survey of 145 providers. Respondents listed delays in patient diagnosis, lack of rare disease education (for physicians and patients alike), and a shortage of physicians specialized in rare diseases as some of the central challenges facing the industry.

So, if a provider wants to expand its team's familiarity with rare diseases, which ones make the most sense to focus on first? Let's explore five of the most common rare diseases affecting patients in the U.S. according to estimates from the Centers for Disease Control and Prevention and the National Institutes of Health.

1. Muscular dystrophy

Muscular dystrophies (MD) are a group of genetic disorders characterized by progressive muscle weakness and degeneration. Duchenne Muscular Dystrophy (DMD) is the most common of these disorders, primarily affecting young boys with symptoms usually appearing around age four.

Although relatively rare, around 250,000 people in the U.S. live with some type of MD. These patients require ongoing, complex care for both mobility and respiratory support. Providers can make the biggest impact by identifying symptoms early. Offering coordinated, multidisciplinary care can help improve quality of life and slow disease progression. Care teams that are unable to staff a specialist in the disease should consider partnering with MD experts who are up to date on the latest treatments and research.

While there's no existing cure for MD, and related muscle damage can't be reversed, gene therapy could eventually enable doctors to replace young patients' mutated genes with healthy copies before the disease progresses.

2. Sickle cell disease

Sickle cell disease (SCD) impacts around 100,000 Americans, primarily those of African American and Hispanic descent. This genetic blood disorder distorts red blood cells into a sickle-like shape, causing painful episodes or "crises", organ damage, and increased infection risk.

As with muscular dystrophy, early intervention and regular monitoring are crucial for managing symptoms and maintaining quality of life. SCD pain crises can be triggered by certain everyday factors, including stress, dehydration, alcohol and tobacco, and even other sources of pain. Because of the self-managed nature of these triggers, early patient education is critical-and also among the biggest challenges facing doctors treating rare diseases, according to our report.

Aside from education and making lifestyle changes to avoid triggers, gene therapy is among the most promising sources of relief for SCD patients. Vertex Pharmaceuticals' Casgevy (exagamglogene automecel) treatment uses a patient's blood stem cells to help their body produce functional red blood cells and reduce or eliminate pain crises.

3. Primary biliary cholangitis

Affecting approximately 65,000 people in the U.S., primary biliary cholangitis (PBC) is a rare autoimmune disease that causes a person's body to gradually damage-and eventually destroy-bile ducts within the liver. Over time, this process leads to cirrhosis of the liver and other symptoms like itching, dry eyes and mouth, and raised cholesterol levels.

PBC predominantly impacts women over 40 and, like the other diseases we've covered, is best managed when detected early. Specialized hepatologists can usually diagnose the disease with a blood test, but medical imaging or more direct examinations of the liver may be necessary.

PBC currently has no cure, but ursodeoxycholic acid can mitigate damage to the liver when taken as an early treatment. In the most extreme cases, a liver transplant may be necessary.

4. Cystic fibrosis

The genetic disorder cystic fibrosis (CF) primarily affects the respiratory and digestive systems, making it difficult for the lungs and gastrointestinal tract to clear mucus. Around 30,000 people in the U.S. live with CF, dealing with frequent lung infections, breathing difficulties, and nutritional deficiencies that can hinder daily life and make physical exertion difficult to tolerate.

The whole-body impact of CF requires providers to adopt a multidisciplinary approach to treatment, with particular focus on pulmonary care, nutrition, and physical therapy. Treatment includes an array of medications for symptoms like respiratory infections and mucus buildup, airway clearing techniques, and lifestyle changes.

Advances in CF care and early diagnosis (newborn screening is increasingly common) have considerably extended patients' life expectancies, and gene therapy may eventually provide a one-time cure, but for now, lifelong disease management remains necessary. For providers looking to grow their rare disease expertise, CF represents a high-value focus area given this need for comprehensive, long-term care.

5. Huntington's disease

Unlike the other rare diseases on this list, Huntington's disease is a neurodegenerative disorder. Inherited through a parent, Huntington's disease is caused by a faulty gene that directs neurons in the brain to deteriorate and die, resulting in progressively declining muscle coordination, cognition, and mental health.

For the 30,000 Americans living with Huntington's disease, careful, ongoing attention from medical specialists is crucial to manage symptoms. An effective interdisciplinary team could include neurologists, behavioral health specialists, and physical therapists, in addition to primary care physicians. Over time, most patients will require a part- or full-time caregiver to support their basic activities of daily living, who will also benefit from medical support and education.

Although Huntington's disease has no cure, gene therapy and stem cell therapy can help reduce the production of the mutant protein responsible for the disease's degenerative effects. As research progresses, these therapies may eventually offer a full cure.

Navigate rare disease care more effectively

While rare disease care may not be at the core of every provider's practice, the prevalence of certain rare diseases makes staff training and appropriate resource allocation a must. Understanding the specific diseases that are most likely to affect patients in your territory or market can help providers optimize resources, improve patient outcomes, and reduce the strain on healthcare teams while maximizing revenue streams associated with the treatment of complex, long-term cases.

Definitive Healthcare offers diagnosis and procedure claims data that can help you identify opportunities for growth and strategic focus in your market, as well as population intelligence featuring clinical propensity modeling and predictive market analytics that allow you to model your market up to 10 years in the future. Sign up for a free trial today and see how our healthcare commercial intelligence platform makes it easier to provide effective and efficient care in the rare disease space.

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