Learn About These Unique Genetic Mutations in Humans

By Jake Schroeder
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The human body’s development can be a tricky business. Different DNA sequences and genomes all play huge roles in things like immune responses and neurological capacities. The genomes people possess are deciding factors in everything all the way down to the color of their eyes, hair and skin tone. When a mutation happens in a genome, it can lead to some unique situations when it comes to how a person’s body looks, how their mind works and how they’re able to use their body.

Uner Tan Syndrome

Uner Tan syndrome was named after a famed Turkish evolutionary biologist after he documented a family living with this condition. People with Uner Tan walk on all fours and often have limited mental capacities and language skills.

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This quadrupedal gait has been attributed to interfamilial reproduction throughout history and is known as an autosomal recessive disorder, meaning a child has to have two copies of the abnormal gene that causes the syndrome. It's also been argued that people develop Uner Tan if they learned to walk on all fours as infants, making balance on two legs very difficult.


Known colloquially as "werewolf syndrome," hypertrichosis is a rare genetic mutation that leads to excessive hair growth on all parts of the body. Both males and females can develop the condition, and only around 40 people with the disorder have been documented across the world.

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Hypertrichosis can be either congenital, in which a mutated gene causes it, or acquired, which means that the disorder develops later in life due to outside factors. Acquired cases are more common and can be attributed to medication use, cancers and eating disorders.

Epidermodysplasia Verruciformis

The autosomal recessive skin condition better known as "treeman syndrome" happens due to a human papillomavirus (HPV) infection. While the body is dealing with HPV, the infection can lead to skin growths that resemble rough tree bark or wood.

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The condition can spread to the entire body but is more likely to stay localized in areas such as the hands or arms, and there’s no treatment for the disorder. The condition affects the body's natural process of sending proteins to zinc stores, leading to the production of the growths.


Severe Combined Immunodeficiency Disorder

When genetic mutations alter the functional development of both T and B cells in a person’s body, they can develop severe combined immunodeficiency (SCID). This creates problems when it comes to being out in a world full of germs because the disorder makes people highly susceptible to getting infections.

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Many people who develop the disorder cannot come into contact with anything outside of their personal disinfected environment. The movie Bubble Boy depicts a character with SCID who can't leave his safe space, lest he risk death, and in real life, it's a much more heartbreaking situation than in the film.


Progeria — or Hutchinson-Gilford progeria syndrome (HGPS) — is an autosomal genetic condition that is found in 1 in every 4 to 8 million people. The genetic disorder causes a person to age significantly faster than the average person.

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Progeria starts to display symptoms within a child’s first few months of life, and more usually appear by the age of 18 months. They include limited growth, hair loss and a recessed jaw. As the child ages, the disease may worsen and lead to kidney failure, blindness and heart problems.

Lesch Nyhan Syndrome

Lesch Nyhan syndrome is a hereditary genetic mutation that happens when there is a deficiency of the gene-encoded enzyme HGPRT in a person’s body. This enzyme is responsible for the proper function of uric acid.

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The condition causes those who have it — around 1 in 400,000 people — to have neurological and cognitive impairments. It also often leads to self-mutilation, such as a person biting their nails down until they bleed. The disorder can also lead to kidney problems and gout.



This congenital disorder happens in the womb when a person’s hands don't develop properly. Typically, the middle fingers on the hand don’t form at all, but sometimes only one may be missing. This results in a split appearance in the hand.

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The middle finger and pointer finger are the main parts of the hand that are usually affected, and the remaining pinky, thumb and ring finger are often still intact, creating a claw-like effect. It can happen to the feet, too. The appearances of the affected hands and feet differ from person to person.

Proteus Syndrome

The rare Proteus syndrome is a genetic mutation that causes tissues to grow abnormally. It also encourages tumor growth throughout an affected person’s body. Named after a Greek god that could change his shape, Proteus syndrome is rare and affects fewer than 1 in 1 million people across the world.

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The condition happens when the mutation of the AKT1 kinase activates. Proteus syndrome usually develops over time in people with the gene. The syndrome has also been referred to as "Elephant Man disease." This is a reference to the famous Joseph Merrick, who may have had the disorder.


A rare genetic syndrome that isn’t seen but is smelled is trimethylaminuria (TMAU). Also known as "fish odor disease," the defect happens when a person’s body’s production of flavin-containing monooxygenase 3 is compromised. This results in metabolic impairment.

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This disorder can lead to buildup of trimethylamine oxide in the body, causing the person's sweat, urine and body to smell like fish. The disorder can change in severity throughout a person’s life, and the strength of the odor can vary at any given time.


Marfan Syndrome

Marfan syndrome is a condition that results in abnormalities in a person’s connective tissues. People who have this disorder are often very tall and thin and may have a problem keeping fat on their bodies. It’s been suggested that Abraham Lincoln had the condition. Marfan syndrome can also lead to scoliosis in some people.

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The autosomal dominant disorder is acquired in the womb when the development of the FBN1 gene mutates. It’s hereditary in 75% of all documented cases. Although there is no cure for Marfan syndrome, there is a treatment for the disorder that can help people live healthier lives.


When the rare genetic disorder anencephaly occurs, a fetus’s brain, skull and scalp develop abnormally — or sometimes not at all. This condition is one of the more tragic, as almost all babies born with it don’t live more than a few days past birth.

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During the process of embryonic development, the neural tube that leads from the brain to the rest of the body is supposed to close. When it doesn't, anencephaly develops. Those born with the condition — who survive — generally face a range of health problems and may need multiple surgeries to replace the missing skull sections, but survival is incredibly rare.


Tetrachromacy is a condition that occurs when a person develops a fourth cone of vision in their eye. This leads to the person being able to see many more colors than the average human being can.

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They can also see more vivid details in the things around them, which gives them a sort of "supervision." Their vision is so keen, in fact, that they're able to see over 100 million colors. Because the mutation is only passed through the X chromosome, the majority of people with tetrachromatic vision are women.



The phenomenon of distichiasis, otherwise known as double eyelashes, might be enviable in some circles, but it's actually a very rare genetic disorder caused by a gene mutation in the womb. Distichiasis can affect both eyes and all four lash lines, or it can be present in just one area of the lash line.

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The FOXC2 gene is responsible for the genetic mutation, and it's not known why that mutation causes the double eyelashes. It’s typically more often attributed to heart problems later on in life and lymphedema-distichiasis syndrome.



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Sirenomelia is an aptly named condition. It’s also known as "mermaid syndrome" because of the significant and distinctive abnormalities it causes. Mermaid syndrome describes a condition in which a person’s legs form together as one instead of separately during fetal development. This creates the look of a mermaid tail.

The condition can also lead to missing parts of the lower spine, problems with kidney function and pelvic abnormalities. Those with the condition also lack aortic branching, which can lead to serious complications later in life, such as heart failure, heart defects and problems with mobility.


It may be a trope in comic books, but cyclopia isn’t entertaining. With this condition, a baby is born with only one eye. The congenital defect happens in the womb when the two eye sockets fail to separate during early development.

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This also leads to development issues with the fetus’s nose, which may not be present at all. If it is, it typically isn't functional. When this genetic mutation happens, affected fetuses are likely to be stillborn or miscarried. Babies born with cyclopia typically only live for a few hours after birth.


Human Vestigiality

Vestigiality usually refers to traits or features that used to exist in living creatures (or potentially existed in those creatures, humans included) but phased themselves out of the evolutionary picture because they were no longer necessary for survival. The most notable of these in people is the tailbone — our early ancestors had tails. Some people still form tails.

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When the coccyx bone in the spine runs longer than it’s supposed to, it generally sticks out and resembles the tail of an animal. Many examples of this defect are present in modern-day medicine and even referenced in movies such as Shallow Hal. Appendixes and wisdom teeth are also vestigial body parts.


Just as the name suggests, gigantism is a genetic mutation that causes a person to grow much larger than the average human being. The rare disorder occurs when the body’s growth hormone production increases, causing the body to accelerate growth during or directly after a person hits puberty.

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There have been a lot of famous instances of gigantism. People who had this condition include Andre the Giant, John Rogan and Robert Wadlow. Babies born with the disorder tend to be of normal weight and size and don’t start their extensive growing until later on.

Underwater Vision

Human eyes usually aren’t that adept at seeing underwater because of the limited amount of refracted light that's able to get through. One rare genetic disorder that affects a small number of people in Thailand makes them able to see everything underwater quite clearly.

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The rare disorder — or possible gift — only appears in this small population. It's assumed that because they spend most of their lives in and around the water, they’ve adapted or evolved to be able to see things underwater, such as creatures hidden in the seabed, that most other people can't.



Polymelia is categorized as a birth defect that causes a fetus to develop extra limbs. It's also theorized that the limbs were once part of a conjoined twin that was absorbed while in utero. The extra limbs are, in many cases, significantly deformed and may not function.

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In a lot of cases, the limb can actually cause problems for the child born with it. If the limb is positioned between the two legs and attached to a certain area of the body, it causes another condition, dipygus, which is described as "a congenital deformity where the body axis forks."


The phenomenon of having two heads isn't just in myths or fairy tales. The rare genetic disorder, although mostly attributed to animals, has happened in humans. In humans, the condition generally occurs with conjoined twins that share the same body or conjoined twins that are joined by the head, ear or brain.

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Having two heads can cause serious problems, depending on how they’re connected. In cases of conjoined twins with two heads that are completely separate, there are two full minds that use one body. In cases in which the brains or heads are connected, severe health problems generally occur.

Reptilian Atavism

Reptilian atavism is another genetic mutation that isn’t visual but instead occurs inside a person’s body. That doesn't make it any less odd — or interesting. The condition is so rare in humans that there have only been a couple of cases documented in the history of the world.

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Reptilian atavism happens when one or more parts of the human body develop in the same way they would in a reptile. The documented cases of this include a person developing a heart that had the same structure as the heart of a snake.


Congenital Methemoglobinemia

Congenital methemoglobinemia is a condition that affects the appearance of a person's skin, lips and nails. This autosomal defect causes a person's skin to turn blue. It’s hereditary and is so rare that the number of cases in the world remains unknown.

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This defect alters a molecule within a person’s hemoglobin, affecting the way oxygen is carried throughout a fetus’s body while in development. Both parents have to possess the mutated gene for the condition to develop, and both parents could appear completely unaffected while still passing on the mutation.

Supernumerary Teeth

The rare condition called hyperdontia occurs when more teeth develop in a person’s mouth than usual. Supernumerary teeth are generally found in people who also have the rare genetic disorder Gardner's syndrome.

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There are a few different types of supernumerary teeth, and the type usually depends on the placement of the teeth within the mouth. One type, conical, is normally rooted and develops around the incisors. The supplemental type usually forms as baby teeth develop, and these fall out along with the baby teeth.


Unlike other genetic mutations that cause extra limbs or heads, diprosopus doesn't involve a conjoined twin. This genetic disorder is characterized as creating "craniofacial duplication," meaning that certain parts of the face or head are doubled (or duplicated.)

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This is generally caused by an abnormality with the body’s Sonic Hedgehog protein (named after the game!). Diprosopus is extremely rare; fewer than 40 cases of the congenital defect have ever been recorded in humans since it was discovered in the late 1800s.


Fibrodysplasia Ossificans Progressiva

Fibrodysplasia ossificans progressiva, otherwise known as FOP, is a genetic defect that is present in fewer than 1 in 2 million people worldwide. Unlike many other genetic defects, FOP is a disabling condition that has no treatment or cure.

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FOP occurs when the tissues and ligaments in a person’s body begin to calcify, eventually turning into bone. The painful process is the only disorder in which one organ system changes into another within the body. Movement is significantly impaired in people with FOP, and it eventually claims the life of anyone who has it.


Congenital insensitivity to pain with anhidrosis (CIPA) is a genetic condition in which the person with the defect has a limited ability — or no ability at all — to feel pain. It’s classified as an autosomal recessive disorder and is passed down from a person’s parents.

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The signs of CIPA start as early as infancy, and because the disorder also prevents sweat glands from functioning properly, infants with the disorder may end up experiencing seizures because of their inability to regulate their body temperatures.

Osteogenesis Imperfecta

Brittle bone disease is a rare genetic disorder that causes the bones in a person’s body to be especially susceptible to breaks, even with very little force applied. The disease can range in severity and can be attributed to problems with collagen production and connective tissue.

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The condition is hereditary. Other symptoms include lung issues, heart issues and blue coloring of the whites of the eyes. The condition might sound familiar — M. Night Shyamalan's character Elijah Price from the films Unbreakable and Glass suffers from the painful condition.


Treacher Collins Syndrome

The autosomal dominant genetic disorder Treacher Collins syndrome, often shortened to TCS, is caused by a new mutation in a person’s genes. This means a person’s parents don’t pass them the gene; however, the condition can be hereditary in rare cases. TSC causes a wide array of physical deformities, often involving the ears, eyes, chin, cheekbones and other parts of the face.

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The condition can be serious and can cause severe health complications, including problems with lung capacity and loss of hearing. The lifespan of those with TSC ranges, but most can live long and healthy lives with facial reconstruction and adaptive aids.


You may know a chimera as a mythological creature or associate the term with animals, but instances of the genetic abnormality do exist in humans. The mutation occurs when certain strands of cells in the body become muddled and blood mixes in the wrong way. It causes a person to carry two different sets of DNA.

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This, in turn, affects the person's development and can contribute to chimera-like attributes. It's not a difficult condition, though, as it doesn't cause much pain or loss of life. The condition can also arise when one fraternal twin dies in the womb and the remaining fetus absorbs it.


Myostatin, otherwise known as "double muscle mutation," is characterized by the presence of double the muscle that a person’s body would normally have. The most notable and known cases are those in small children who are super-strong for their age and expected abilities.

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The super-strength mutation is generally hereditary, and only one parent has to possess the myostatin gene for a child to develop this condition. Some cases have also been reported that are attributed to the myostatin receptors in the body, not the gene. Myostatin is very rare in humans and is usually seen in animals.