Ten Rare Diseases You May Never Have Heard Of

A disease is considered rare when it impacts fewer than 200,000 people in the U.S. There are over 10,000 rare diseases that affect more than 30 million Americans. In 2025, February 28th is Rare Disease Day to raise awareness of and support for those living with such diseases. To support that day, here is some info about 10 rare diseases you may not have heard of.

Addison’s Disease/Primary adrenal insufficiency

The adrenal glands produce two important hormones: cortisol and aldosterone. These hormones help regulate metabolism and blood pressure. When the glands are not producing enough of these, the result is Addison’s disease. The most common cause? An autoimmune disorder where the body’s own immune system gets confused and starts attacking the adrenal glands.

Addison’s disease symptoms can include fatigue, weakness, nausea, loss of appetite, stomach pain, salt cravings, and darker skin or gums. These symptoms usually develop slowly and are often mistaken for other common illnesses. A serious complication of Addison’s disease is an adrenal crisis, which happens when the adrenal glands fail completely and requires emergency treatment. Adrenal crises can be triggered by stress, dehydration, injury, infection, or missed medication for those with adrenal insufficiency.

Doctors diagnose Addison’s disease by looking at a patient’s medical history, doing a check-up, and running some blood tests. These tests are usually done in the morning because that’s when cortisol levels should be at their peak.

Addison’s disease is managed with daily steroid pills such as Prednisone or Florinef, which are usually lifelong medications. Sticking to the treatment plan is extremely important to avoid serious issues like adrenal crises. Regular checkups and blood tests help doctors tweak the dose when needed.

Childhood Dementia Disorders

Childhood dementia refers to over 100 rare genetic conditions that cause worsening brain damage in kids. In some cases, it’s not inherited and just happens due to random DNA changes early in life. Symptoms don’t always show up at birth and can vary from child to child. As the condition progresses, children gradually lose abilities like talking, walking, reading, and playing. Over time, their brain also struggles to control basic body functions, which can be terminal.

Childhood dementia has a lot in common with adult dementia, including challenges like memory loss, confusion, trouble focusing, learning, and communicating. Kids might also experience personality changes, sleep issues, or emotional and behavioral ups and downs. Depending on the type, some children might have seizures or face problems with their bones, heart, lungs, or digestion. In some cases, they can even lose abilities like seeing, hearing, or moving.

Childhood dementia is often diagnosed late because the early symptoms are vague, the diseases are rare, and many doctors aren’t familiar with them. Kids are often misdiagnosed with conditions like autism, developmental delays, or ADHD. Most childhood dementia disorders have no cure, and existing treatments usually only slow the disease’s progression.

Homocystinuria

Homocystinuria (HCU) is a rare genetic condition that runs in families. It happens when an enzyme called cystathionine-ß-synthase isn’t doing its job. As a result, a substance called homocysteine builds up in the blood and urine because the body can’t process it properly into cysteine. Over time, this can cause some serious health problems if left unchecked. Homocystinuria can affect various parts of the body, including the eyes, skeletal system, central nervous system, and vascular system. Eye-related symptoms include severe nearsightedness (myopia) and lens dislocation (ectopia lentis). In the skeletal system, individuals may experience excessive growth, long limbs and fingers, knock knees, a sunken or protruding chest, spine curvature (scoliosis), and an increased risk of early osteoporosis. The condition can also cause developmental delays, learning difficulties, and an increased risk of blood clots.

Treating homocystinuria is all about keeping homocysteine levels in check. This usually means cutting back on high-protein foods and adding the right supplements to balance things out. Doctors often prescribe vitamin B6 supplements, Cyanocobalamin (B12) shots, and Betaine to bring those levels down. Sometimes, they add vitamin C for a little extra support. About half of all people with HCU respond well to vitamin B6 alone.

Hypopituitarism

Hypopituitarism is a condition resulting from reduced levels of some hormones that come from the pituitary gland, sometimes called the “master gland,” that results in various symptoms depending on which hormone is low. This usually occurs when the front part of the gland isn’t working correctly or stops altogether. There are many possible causes for this. Sometimes, tumors, blood flow issues, infections, autoimmune problems, head injuries, or even treatments like radiation or surgery can cause the gland to stop working effectively. Less commonly, it could be conditions like sarcoidosis or amyloidosis, which involve inflammation or unusual protein buildup in tissues.

Sometimes, problems with the hypothalamus, the brain’s “control center” for the pituitary, can indirectly cause these problems. Tumors, inflammation, head injuries, or even surgery can affect blood vessels or nerves that the pituitary gland needs to function.

Hypopituitarism is diagnosed through a review of the patient’s medical history and a physical exam. Doctors may also use tests like CT scans or MRIs to get detailed images of the body. Blood and urine tests are done to check hormone levels and identify any imbalances.

Hypopituitarism treatment varies depending on the cause. Doctors decide the best approach based on a patient’s age, overall health, severity of symptoms, and ability to handle treatments. Options may include medications, therapies, or procedures, all with the goal is to restore the pituitary gland’s normal function.

Maple Syrup Urine Disease (MSUD)

Maple Syrup Urine Disease is a rare genetic condition with a pretty unusual name. It happens when the body can’t properly break down three branch-chain amino acids, leucine, isoleucine, and valine, because of an issue with a specific enzyme. As these build up, they can cause some serious problems, including damage to the brain. The name comes from the sweet, syrupy smell of the urine, which is caused by the buildup of some chemicals.

Managing MSUD means sticking to a low-protein diet and avoiding foods and supplements that contain these branched-chain amino acids. Thanks to newborn screening and proper treatment, most people with MSUD can live healthy and happy lives.

Myasthenia Gravis

Myasthenia gravis (MG) is a condition where the immune system attacks the connection between nerves and muscles, causing muscle weakness and fatigue. It affects voluntary muscles, like those used for eye movement, facial expressions, talking, chewing, swallowing, and moving arms or legs. Symptoms often get worse with activity but may improve after rest. Heat and stress can also make it worse. In serious cases, MG can affect the muscles used for breathing, which can become life-threatening.

Symptoms of Myasthenia gravis tend to appear in women under 40 and men over 50, but it can also affect kids under 18, known as juvenile MG. There’s even a temporary version called neonatal MG, which sometimes happens to newborns if their moms have MG. This happens when certain antibodies cross over the placenta, leading to weak muscles or feeding troubles for the baby.

Myasthenia gravis (MG) is a chronic condition that requires ongoing treatment, though some people may go into remission and have no symptoms. Treatments for MG can include:

• Medications with anti-acetylcholinesterase agents, which work quickly to improve symptoms but wear off fast.
• Immune-suppressing drugs like corticosteroids or other agents to reduce the immune system’s attack on the body.
• Plasmapheresis, a process that removes harmful antibodies from the blood and replaces the plasma.
• Intravenous immunoglobulin (IVIg), which infuses healthy plasma from donors.

In some cases, doctors may recommend removing the thymus gland (thymectomy) to help manage the condition. The best treatment depends on a person’s specific symptoms and complications.

Neuromuscular conditions

Neuromuscular conditions are disorders that affect the muscles and the nerves that control them. Normally, the brain sends signals through the nervous system to make the muscles move and work properly. In these conditions, this process is disrupted, leading to problems with muscle strength and function.

In some cases, nerve damage can stop signals from reaching the muscles, or muscles might not respond properly to the signals. This can lead to muscle loss (atrophy) and, in severe cases, physical disability. Sometimes, the problem is at the neuromuscular junction, where nerves and muscles connect, preventing signals from passing through. Symptoms vary depending on the type of condition and which nerves or muscles are affected. Here are some common types:

• Myopathies: Genetic diseases that weaken muscles used for movement, like in muscular dystrophy, where muscles break down over time.
• Motor neuron diseases: These damage motor nerves, leading to muscle weakness that gets worse over time.
• Peripheral neuropathies: These affect the nerves in the hands, feet, arms, or legs, causing issues with movement and feeling.
• Neuromuscular junction diseases: These block signals between nerves and muscles, preventing them from working properly.

Neuromuscular conditions can be caused by all kinds of things, including genetic mutations, autoimmune issues, hormone imbalances, viral infections, poor nutrition, certain medications, or even exposure to toxins. Sometimes, though, the cause remains a mystery.

To diagnose, doctors rely on tests like nerve conduction studies (to see how well nerves are working) and EMGs (to check how muscles are responding). They might also use muscle biopsies, blood tests, or genetic testing if they suspect it’s something inherited. Since most of these conditions don’t have a cure, the focus is on managing symptoms to improve quality of life.

Prolactinoma

A prolactinoma is a noncancerous growth in the pituitary gland that makes the body produce too much prolactin, a hormone that helps with breast tissue development and milk production. It also plays a role in other bodily functions. When prolactin levels get too high due to these growths, it can lead to things like infertility and other health issues. The good news? Prolactinomas aren’t usually life-threatening. 

Prolactinomas come in two sizes: microprolactinomas and macroprolactinomas. Microprolactinomas are tiny, less than one centimeter wide, and tend to show up more often in females. Macroprolactinomas, on the other hand, are over one centimeter wide and are more common in males.

Prolactinoma symptoms can include milky nipple discharge, low sex drive, infertility, and erectile dysfunction. It can affect anyone, but females often notice symptoms earlier than males.

Prolactinoma is diagnosed through symptoms, medical history, and a physical exam. If there’s milky discharge from the nipples, a breast exam may be done. Common tests include:

• Prolactin blood test: High prolactin levels in the blood may indicate a prolactinoma. Imaging tests are usually done next to confirm.
• MRI or CT scan: These scans locate the tumor and show its size. MRI is preferred, but a CT scan may be used if MRI isn’t an option.
• Testosterone blood test: For males, testosterone levels are often checked to help with diagnosis. Low testosterone levels can be easily fixed with AndroForte 5% Cream.

Doctors often treat prolactinomas with medications called dopamine agonists, such as Dostinex or Parlodel. These drugs help shrink the tumor and lower prolactin levels to normal. 

Patients usually need to take one of these medications for about two years to help stop the tumor from returning, especially if it’s large. If prolactin levels are normal and the tumor is gone after this time, the doctor may gradually lower the dosage and eventually stop the medication.

Coxiella Burnetii Fever; Q Fever Pneumonia; Query Fever

Q Fever is an illness caused by bacteria spread by animals like cattle, sheep, and goats through their birth fluids, milk, urine, or feces. The bacteria can survive in the environment for a long time and infect people who breathe in contaminated dust or droplets. While humans can catch Q Fever, it rarely spreads from person to person.

Most people infected with Q fever don’t show any symptoms. For those who do, it often feels like a bad case of the flu. In rare cases, it can cause problems with the heart, muscles, or nervous system. Infections during pregnancy may lead to miscarriage, slow fetal growth, or early birth. Quick diagnosis and treatment are important, as the infection can sometimes become chronic and cause serious complications. Those most at risk of chronic Q fever include people with weakened immune systems, pregnant women, and individuals with heart conditions.

There’s a vaccine for Q Fever for those at risk, but an immunity test is needed first. If someone’s already had Q Fever, the vaccine is not recommended due to the risk of side effects. Staying safe is also about basics like good hygiene, wearing protective gear, and properly handling animal waste and birth materials. For acute Q Fever, antibiotics are usually prescribed in the short term, especially if caught early. Chronic Q Fever, though, might mean longer-term antibiotic treatment.

WHIM syndrome

WHIM syndrome is a rare genetic condition that throws the immune system off balance. The name comes from its main features: warts (W), low antibody levels (H for hypogammaglobulinemia), infections (I), and myelokathexis (M). Basically, hypogammaglobulinemia means the body doesn’t have enough antibodies to fight off germs. Myelokathexis, on the other hand, happens when white blood cells (called neutrophils) get stuck in the bone marrow instead of moving to the bloodstream, which leads to low neutrophil levels (neutropenia).

People with WHIM syndrome tend to get repeated bacterial infections, which can sometimes lead to issues like hearing loss. They might also get warts from HPV infections and face a slightly higher risk of certain cancers. Symptoms usually begin in early childhood, starting with frequent bacterial infections. They might also pick up viral or fungal infections. HPV-related warts can also appear, often spreading and being difficult to get rid of.

WHIM syndrome is the result of a mutation in the CXCR4 gene, which controls a protein called the CXCR4 receptor. This problem causes the protein to fail to work properly. The condition runs in families and is autosomal dominant. This means that if someone inherits just one copy of the changed gene, they can have the syndrome.

Doctors diagnose WHIM syndrome by examining a patient’s medical history, performing a physical checkup, and running blood tests. Genetic testing can also help by identifying changes in the CXCR4 gene. Sometimes, they might perform a bone marrow biopsy. WHIM syndrome can be a suspect for anyone who has had multiple bacterial infections as a child, with or without warts.

There is no widely agreed-upon treatment for WHIM syndrome. Doctors focus on managing symptoms, such as using medications to treat infections and warts. People with frequent infections may also receive antibiotics to help prevent them.

FAQs

What is a rare disease?

In the United States, a rare disease is classified as a condition impacting fewer than 200,000 people. Similarly, in the European Union, legislation introduced in 2000 defines a rare disease as one that affects no more than five individuals per 10,000 people.

What are the chances of getting a rare disease?

These conditions affect a significant part of the population, even if they aren’t widely talked about. Around 30 million people in the US, or 1 in 10, live with a rare disease. 

What is the rarest disease in the world?

Fields condition, or Fields’ disease, is an extremely rare neuromuscular disorder believed to be the rarest medical condition globally. It is named after Welsh identical twins Catherine and Kirstie Fields, who, along with one other individual, are the only known cases of the condition.