Top 10 Rarest Diseases You've Never Heard Of

Script written by Noah Achod.

There are some mystery diseases you may never have heard of. From Foreign Accent Syndrome, to the Tree Man Illness, to Hutchinson-Gilford Progeria Syndrome – which inspired “The Curious Case of Benjamin Button” – these are some of the strangest known medical conditions. WatchMojo counts down ten fascinating rare illnesses.

Special thanks to our users Ayoub Mahmoud, Dubstep Choo Chen Ling, MikeMJPMUNCH, EmJay and RedHood for suggesting this idea! Check out the voting page at WatchMojo.comsuggest/Top%20Ten%20Rarest%20Diseases


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Script written by George Pacheco.

Top 10 Rarest Diseases You've Never Heard Of

One in a million? What are the odds? Welcome to, and today we’re counting down our picks for the Top 10 Rarest Conditions and Diseases.

For this list, we’re ranking the medical conditions that occur the least among the human population. These diseases either tend to be found in one specific area of the world, or otherwise rarely present within large groups of people, and tend to carry with them some very bizarre symptoms.

#10: Foreign Accent Syndrome

Between 1941 and 2009, 62 cases of the speech condition known as foreign accent syndrome (or F.A.S.) were reported. First discovered in 1907, F.A.S. is characterized by the subject speaking their native language with an accent that is foreign to them. So imagine a born-and-raised New Yorker suddenly speaking with a deep, southern drawl or like a member of British aristocracy. In some cases, rather than an accent, a person’s pitch or ability to correctly pronounce syllables may be affected. F.A.S. can be brought on by a stroke or some form of head trauma, with patients sometimes comparing the symptoms to those associated with a speech disorder.

#9: Microcephaly

The connection between the Zika virus in pregnant women and children born with microcephaly brought significant attention to this disorder. Microcephaly generally presents at birth or early in a child’s development. Children born with the condition exhibit a lack of brain development and a head much smaller than normal. Side effects include intellectual disabilities and low motor function, as well as a propensity for seizures and dwarfism. The lifespan is also typically affected. Although there have been cases where those suffering from this condition went on to lead a normal life, usually the impaired brain function has a significant negative impact.

#8: Epidermodysplasia Verruciformis

The human body is a strange and mysterious thing that can fall victim to a number of equally strange diseases. Case in point: the hereditary skin disease epidermodysplasia verruciformis, aka the “tree man illness.” The disease, which is often abbreviated to EV, occurs as a result of a PH mutation within the genes. EV affects the body’s resilience to human papillomaviruses on the skin, often infecting the patient with uncontrolled, scale-like growths. These growths often take on the appearance of tree-like appendages growing from the hands or feet. Remarkably resistant to both medication and surgery, EV patients have been treated with some success, but they usually require repeated treatments.

#7: Fibrodysplasia Ossificans Progressiva (FOP)

Our bodies can be incredibly efficient healing machines, but what happens when that natural repair process goes wrong? This is the situation with fibrodysplasia ossificans progressiva, or F.O.P. This disease of the connective tissue affects the body’s ability to naturally heal its supply of fibrous tissue, like muscles, joints and ligaments. Translation? When someone afflicted with F.O.P. is injured, their body repairs itself not by growing health, new tissue, but by growing bone. Sometimes, this results in joints that are literally frozen by the process of ossification.

#6: Hutchinson-Gilford Progeria Syndrome

Although “The Curious Case of Benjamin Button” is said to have been inspired by Hutchinson-Gilford progeria syndrome, the condition in real life is quite different. Babies born with this extremely rare genetic disorder, often simply called progeria, seem to age at a vastly accelerated rate. Few live beyond their early 20s, and most exhibit symptoms of the disease shortly after birth. These symptoms start with a failure to thrive as other babies do, along with a hardening of the skin. Other symptoms include brittle bones, hair loss, reduced eyesight, wrinkled skin and excessive weight loss. Essentially, the young child seems to be aging way faster than they should be. Sadly, there is no cure.

#5: Harlequin-Type Ichthyosis

Remarkable advances in the area of neo-natal care have proven to be a godsend for those suffering from the extremely rare skin condition known as Harlequin Type Ichthyosis. This disease is distinguished by the presence of a thick, hard, armor-like plate of dry skin all over the body. Dehydration and respiratory issues are common, as is serious infection due to the skin’s cracked, arid nature. This disease was almost always fatal to infants when it was first seen during the mid-1700s. Today, however, early care and treatment means that babies born with harlequin type ichthyosis now have a fighting chance for survival.

#4: Congenital Analgesia

We’ve all daydreamed about being a superhero and being able to withstand an enormous amount of pain or damage without batting an eye. But what would happen if we actually couldn’t feel any pain whatsoever? Would this really be a good thing? Not according to those who suffer from congenital analgesia, a rare and dangerous disorder which does just that: affects the body’s ability to feel pain. Doctors believe an excessive amount of endorphins produced in the brain cause this condition. Unfortunately, this exacerbates damage to the body rather than diminishing it. Many of those afflicted by C.A. have reported biting off their own tongue, breaking bones or suffering severe infections.

#3: Alström Syndrome

Alstrom syndrome, or Alström-Halgren syndrome, as it’s sometimes known, is one of the most recently discovered conditions on our list. First reported in 1959 by Swedish psychiatrist Carl-Henry Alström, it’s also one of the rarest conditions, with just over 500 cases having been reported over the world. Alström Syndrome can usually be seen in infancy, characterized by a wide array of severe organ issues. Obesity, blindness, loss of hearing and diabetes are just a few of the symptoms associated with A.S. Few live past age 50, due largely to the fact that there’s currently no cure for the disease, only therapy and treatment.

#2: Fields’ Disease

No medical condition is rarer than the neuromuscular condition known as Fields’ disease. Only two cases have been reported to date: the twin sisters Catherine and Kirstie Fields for whom the disease is named. In 1998, their parents noticed some initial problems; within five years, the girls were suffering from severe muscular degeneration, eventually losing their ability to speak and requiring walkers to assist in mobility. Meanwhile, neurological issues caused severe shaking and trembling hands. Though difficult to manage, a 2012 update from Britain’s The Daily Mirror showed the girls in good spirits after they were given speech devices similar to those used by Stephen Hawking.

Before we name our rarest medical condition, here are a few honorable mentions:
- Paraneoplastic Pemphigus (PNP)

- Xeroderma Pigmentosum

#1: Aquagenic Urticaria

Some people can’t swim. Some folks just hate the water, but what if exposure to H20 actually caused you intense, physical pain? Those who suffer from aquagenic urticaria, an intense skin reaction to water, contend with this problem on a daily basis. Red, itchy hives can emerge on the skin only minutes after exposure. What’s more, there’s no cure for aquagenic urticaria, which is more likely to occur in women than men. Only antihistamines, steroids, radiation or medication offer limited comfort to those for whom every shower or hand washing session is a challenge.

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