20 Diseases You've Probably Never Heard Of

This very rare disorder is characterized by an unusually extreme "startle" reaction. It was first identified in the late 1800s among an isolated group of French Canadian lumberjacks. The exact cause of jumping Frenchmen of Maine is unknown. One theory is that the disorder occurs because of an extreme conditioned response to a particular situation influenced by cultural factors.

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In this acquired (not inherited) disorder, skin and soft tissues on half of the face begin to shrink (atrophy), leading to a non-symetrical appearance. Typically, symptoms first appear before age 20, and there is great variation in the degree of severity. The cause of the syndrome -- also known as HFA, progressive facial hemiatrophy, PRS or Romberg syndrome - is unknown.

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This rare genetic disorder causes multiple strokes in adults, even young adults, and may progress to cause cognitive impairment and dementia. The symptoms of CADASIL are caused by damage to small blood vessels, especially those in the brain. Also known as Hereditary Multi-infarct Dementia, the symptoms and progression of the disease vary widely.

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This disease is caused by the absence or deficiency of an enzyme. Symptoms include impaired kidney function, joint pain and self-mutilating behaviors such as lip and finger biting and/or head-banging. Additional symptoms may include muscle weakness (hypotonia), uncontrolled muscle movements and neurological impairment. Other names for it include HGPRT or HPRT deficiency, or hypoxanthine-guanine phosphoribosyl transferase deficiency.

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Symptoms of this very rare disease include loss of taste, intestinal polyps, hair loss and nail growth problems. CCS occurs mostly in older people. There have been fewer than 400 cases reported in the past 50 years, primarily in Japan but also in the U.S. and other countries.

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This extremely rare genetic disorder is characterized by severe insulin resistance. Initial symptoms include abnormalities of the head and face, teeth, nails and skin. Other symptoms include skin abnormalities such as acanthosis nigricans, a skin disorder characterized by abnormally increased coloration (hyperpigmentation). In most cases, additional symptoms are present. Rabson-Mendenhall syndrome is inherited as an autosomal recessive trait, according to NORD.

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This is a rare malignant growth characterized by progressive accumulation of mucous-secreting tumor cells within the abdomen and pelvis. Symptoms include increasing size of the abdomen and abdominal pain. The disorder develops after a small growth (polyp) located within the appendix bursts through the wall of the appendix, and spreads mucus-producing tumor cells throughout the surrounding surfaces. Other names for Pseudomyxoma Peritonei include colloid carcinoma, malignant appendiceal tumor, malignant large Bowel tumor, peritoneal carcinomatosis and pseudomyxoma ovarii.

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This genetic disease is characterized by blisters and lesions that may come and go, usually healing without scarring. It becomes apparent after puberty and occurs because of a mutation in a gene responsible for production of a protein essential for good skin health.

Also known as benign chronic familial pemphigus or HHD, Hailey-Hailey occurs due to a mutation in a specific gene that creates a protein that is essential for the proper health of skin, according to the NORD Web site. The disorder becomes apparent after puberty and symptoms can develop at any age.

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POEMS is an acronym that stands for Polyneuropathy (affecting many nerves), Organomegaly (abnormal enlargement of an organ), Endocrinopathy (affecting certain hormone-producing glands), Monoclonal gammopathy and skin defects. Symptoms include progressive weakness of the nerves in the arms and legs, enlarged liver or spleen, darkening of the skin and excessive hair growth. Other names for the disorder include Crow-Fukase Syndrome, Takatsuki syndrome and PEP Syndrome.

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This is a genetic disorder of copper metabolism that is detectable before birth, follows a progressively degenerative path, and involves several organs of the body but especially the brain. Symptoms may include seizures, stunted growth, unstable body temperature and unusual color or texture of hair. Other names for the disease include Copper Transport Disease, Kinky or Steely Hair Disease or Trichopoliodystrophy.

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This refers to a brain malformation that occurs during embryonic development of the cerebellum and 4th ventricle. Symptoms may include developmental delay, low muscle tone (hypotonia) or spasticity, and poor coordination and balance. In addition, DWM is sometimes (20-80%) associated with hydrocephalus, in which blockage of the normal flow of spinal fluid leads to excessive amounts of fluid accumulating in and around the brain. This leads to abnormally high pressure within the skull and swelling of the head, and can lead to neurological impairment.

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This rare autoinflammatory disorder (sometimes referred to as AOSD or Wissler-Fanconi Syndrome) affects the entire body. The cause is unknown. Affected individuals may develop episodes of high, spiking fevers, a pink or salmon-colored rash, joint pain, muscle pain and sore throat. Episodes vary in frequency and severity.

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This is a group of rare conditions characterized by prenatal development of an abnormally small cerebellum and brain stem. It is usually associated with profound intellectual disability. These diseases are uniformly fatal in early life; only a few patients have reached their 20s or 30s.

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This genetic disease is characterized by the complete absence of an enzyme required to break down certain fats in the body. These fats accumulate in tissues and organs, causing various symptoms that may include swelling of the abdomen, vomiting and enlargement of the liver or spleen.

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This is a group of diseases affecting the immune system. LAD syndromes are characterized by defects affecting how white blood cells respond and travel to the site of a wound or infection. Symptoms vary from person to person, but all who are affected develop an increased susceptibility to recurrent bacterial and fungal infections.

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This is a rare but very severe type of bacterial infection that can destroy muscles, skin and underlying tissue. "Necrotizing" refers to something that causes tissue death. These infections can be sudden, vicious and fast-spreading, and if not treated quickly, can lead to toxic shock syndrome. Other names for the disease include flesh-eating bacteria (or disease) and streptococcal gangrene.

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This genetic disease is characterized by early onset of cataracts associated with persistently elevated levels of a protein known as ferritin in the blood plasma. The mutation associated with this disease is inherited as an autosomal dominant trait, and cataracts are the only known complication associated with this rare disease.

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This is a rare genetic disorder that may be apparent at birth or in the first year of life. It is characterized by mental retardation, distinctive facial features and seizures. The presence of this syndrome may not be realized until childhood or early adulthood. Some affected individuals may also have a gastrointestinal disease known as Hirschsprung disease.

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This is a rare multisystem disease of adulthood. It is characterized by excessive production and accumulation of histiocytes (a type of cell) within multiple tissues and organs. The underlying cause is unknown.

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This rare genetic disorder is characterized by an uncoordinated or clumsy manner of walking and dystonia (a general term for a group of muscle disorders characterized by involuntary contractions). Symptoms usually become apparent around six years of age and may be more noticeable in the afternoon or evening than in the morning.

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For more information about rare diseases, see the links on the next page.