Updated 24 June 2013

6 very rare diseases

A doctor might go through a whole career without ever seeing any patients with any of these very rare diseases. But they are out there.


Common diseases are scary enough, but then there are those conditions that afflict only a few people. These conditions often go undiagnosed for years, as doctors might come across only one case (or none at all) during their whole career.

A disease is regarded as rare if fewer than 200 000 people in the United States have it. These are often also called “orphan” diseases. There are close to 7 000 rare diseases and about 25 million people in the US have one. Many rare diseases are caused by changes in genes and are called genetic diseases.

As there are so many rare conditions, it would be close to impossible (and somewhat pointless) to determine which is the rarest.

These 6 specifically drew attention when it came to afflictions you are unlikely to come across, or suffer from:

Morgellons. The Centre for Disease Control get reports every now and then of an unexplained skin condition also known as "Morgellons".  The name comes from an unrelated condition involving "black hairs" emerging from the skin of children that was documented in France in the 1600s.

Patients report skin sensations which include crawling, biting and stinging. They also report threads or black specks on or under the skin. They also frequently have skin rashes or sores. Furthermore, this condition is often accompanied by memory loss, confusion, and changes in vision. According to the Morgellons Research Foundation, more than 13 000 families in the US have reported suffering from the disease.

A growing number of doctors believe Morgellons to be a chronic infectious disease and not something that results from contact with aliens, as some fringe websites suggest.

Fields' disease. This is considered the rarest known disease in the world, with only two cases diagnosed. It is named after Welsh twins Catherine and Kirstie Fields who were diagnosed with it at the age of four. This disease is a neuromuscular disease, which results in muscular degeneration.

As these twins are thought to be the only know sufferers in the world, it is not known what the likely prognosis of the disease is. That also makes it the rarest disease in the world.

Kuru. This is a disease of the nervous system. In Papua New Guinea, many tribes practised cannibalism for ritualistic purposes until the 1960s. It was found that many of them suffered from a disease called “kuru”, which they had contracted from eating human tissue. It was thought to be a form of human “mad cow disease”. Over a couple of decades, only a few thousand cases were reported, according to the Journal of Epidemiology in 2002.

Symptoms of kuru include arm and leg pain, co-ordination problems that become severe, difficulty walking, headaches, difficulty swallowing, tremors and muscle jerks, and being unable to feed oneself. This can lead to malnutrition or starvation.

The average time from exposure to symptoms (incubation period) is 10 to 13 years, but incubation periods of 30 years or even longer have been reported.

Microcephaly is a medical condition in which the circumference of the head is smaller than normal, because the brain has not developed properly or has stopped growing. Microcephaly can be present at birth or it may develop in the first few years of life. 

 It is most often caused by genetic abnormalities that interfere with the growth of the cerebral cortex during the early months of foetal development, according to the National institutes of Health. It is thought that this affects only one in about 7000 babies.

Von Hippel-Landau (VHL) is a rare, genetic multi-system disorder characterised by the abnormal growth of tumours in certain parts of the body. The tumours of the central nervous system (CNS) are benign and are comprised of a nest of blood vessels and are called haemangioblastomas. Other types of tumours develop in the adrenal glands, the kidneys, or the pancreas.

Symptoms of VHL vary among patients and depend on the size and location of the tumours. Symptoms may include headaches, problems with balance and walking, dizziness, weakness of the limbs, vision problems, and high blood pressure. Cysts (fluid-filled sacs) and/or tumours (benign or cancerous) may develop around the hemangioblastomas and cause the symptoms listed above. Individuals with VHL are also at a higher risk than normal for certain types of cancer, especially kidney cancer, according to the National Institutes of Health.

Once thought to be extremely rare, it is now thought that many people have it without knowing it. It often only manifests very late in life.

Progeria is a rare condition that results in rapid ageing in children. The full name of the condition is Hutchinson- Gilford Progeria Syndrome. It usually is not passed down through families. Rarely is it seen in more than one child in a family. It is thought to affect about one child in every 8 million live births.

Symptoms of progeria include growth failure during the first year of life, narrow, shrunken or wrinkled face, baldness, short stature, large head for size of face, dry scaly thin skin, among others.

(References:;;, medline plus)

(Susan Erasmus,, November 2011) 


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