10 Unusual Genetic Mutations in Humans
1/30/18, 2)02 PM
10 Unusual Genetic Mutations in
Humans
George Dvorsky 4/05/13 2:01pm
No two people are alike, due to the subtly different ways our genomes are
expressed. But sometimes these biological differences lead to genetic
mutations that are extremely rare, and sometimes debilitating. Historically,
many people suffering from these mutations were labeled monsters or freaks
— but today, we know they are simply part of the broad spectrum of genetic
variations in our species. Here are 10 of the most unusual genetic mutations
we've identified in humans.
1. Progeria
This genetic disorder is as rare as it is severe. The classic form of the disease,
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called Hutchinson-Gilford Progeria, causes accelerated aging.
Most children who have progeria essentially die of age-related diseases
around the age of 13, but some can live into their 20s. Death is typically
caused by a heart attack or stroke. It affects as few as one per eight million
live births.
The disease is caused by a mutation in the LMNA gene, a protein that
provides support to the cell nucleus. Other symptoms of progeria include
rigid (sclerotic) skin, full body baldness (alopecia), bone abnormalities,
growth impairment, and a characteristic “sculptured” nasal tip.
Progeria is of great interest to gerontologists who hope connect genetic
factors to the aging process. Image: HBO.
2. Uner Tan Syndrome
Uner Tan syndrome is a somewhat controversial condition, whose most
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obvious property is that people who
suffer from it walk on all fours. UTS is a
syndrome that was proposed by the
Turkish evolutionary biologist Üner Tan
after studying five members of the Ulaş
family in rural Turkey. These individuals
walk with a quadrupedal locomotion, use
primitive speech, and have a congenital brain impairment (including
“disturbed conscious experience”). The family was featured in a 2006 BBC2
documentary called, "The Family That Walks On All Fours." Tan describes it
like this:
The genetic nature of this syndrome suggests a backward stage in human
evolution, which is most probably caused by a genetic mutation,
rendering, in turn, the transition from quadrupedality to bipedality. This
would then be consistent with theories of punctuated evolution.
The new syndrome, says Tan, “may be used as a live model for human
evolution.” Some experts think this is bunk, and that genetics may have very
little to do with it.
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3. Hypertrichosis
Hypertrichosis is also called “werewolf syndrome” or Ambras syndrome, and
it affects as few as one in a billion people; and in fact, only 50 cases have been
documented since the Middle Ages.
People with hypertrichosis have excessive hair on the shoulders, face,
and ears. Studies have implicated it to a rearrangement of chromosome 8. It
happens due to a disruption of the “crosstalk” between the epidermis and the
dermis as hair follicles form in the 3-month fetus at the eyebrows and down
to the toes. Normally, signals from the dermis send the messages to form
follicles. As a follicle forms, it sends signals to prevent the area around it from
also becoming a follicle, which results in the equal spacing of our five million
or so follicles. Most of our body parts ignore the messages to form follicles,
which explains why most of us are relatively hairless.
4. Epidermodysplasia Verruciformis
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Epidermodysplasia verruciformis is an
extremely rare disorder that makes
people prone to widespread human
papillomavirus (HPV) infection.
This infection causes scaly macules and
papules (cutaneous squamous cell
carcinomas) to grow on the hands, feet,
and even face. These skin “eruptions”
appear as wart-like lesions — and
even wood-like and horn-like
growths — with reddish-brown
pigmented plaques. Typically, the skin
tumors start to emerge in people between
the age of 20 and 40, and the growths
tend to appear on areas exposed to the
sun. Also called Lewandowsky-Lutz dysplasia, there is no known cure, though
treatments to scale back the growths are possible.
The disorder was brought to the public’s attention in November 2007 when a
video of a 34-year-old Indonesian man named Dede Koswara appeared on the
internet. In 2008, he underwent surgery to have 13 pounds (6 kg) of the warts
removed. After the lesions and horns were extracted from his hands, head,
torso, and feet, his hands were grafted with new skin. In all, about 95% of the
warts were removed.
5. Severe Combined Immunodeficiency Disorder (SCID)
Also known as the Boy in the Bubble Disease, it’s a disorder in which
individuals are born without an effective immune system.
The disease was made famous by virtue of the 1976 film, The Boy in the
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Plastic Bubble, a story inspired by the
lives of David Vetter and Ted deVita. In
the movie, a boy is forced to live in plastic
isolation for fear of exposure to unfiltered
air and the introduction of lifethreatening pathogens. In real life, Vetter
lived in this condition for 13 years, but he
died in 1984 following an unsuccessful
bone marrow transplant (a failed attempt to help him fight infections).
And indeed, the disorder is caused by a number of genes, including those that
cause defects in both T and B cell responses — which has a downstream
negative effect on the production of lymphocytes (a type of white blood cell).
SCID is also thought to arise due to the lack of adenosine deaminase (ADA).
Interestingly, SCID was the first human illness treated by human gene
therapy in 1990, and is increasingly being used to treat children. Image:
Baylor College of Medicine Archives.
6. Lesch–Nyhan Syndrome
LNS is a genetic disorder that affects one
in every 380,000 births, nearly all of
them boys. It results in an
overproduction of uric acid — a waste
product of normal chemical processes
that’s found in blood and urine. But
individuals with Lesch-Nyhan release
excess uric acid through their blood
which builds up under the skin causing
gouty arthritis. It can also cause kidney
and bladder stones.
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The disease also affects neurological function and behavior. Individuals
exhibit involuntary body movements, like tensing muscles, jerking
movements, and flailing limbs. Self-mutilating behaviors are also
common, including head banging, and lip and finger biting. Individuals can
be given allopurinol to help with the gout, but treatments for the neurological
and behavioral aspects of the disease remain out of reach.
7. Ectrodactyly
Formerly known as “lobster claw hand, ”individuals with this disorder have a
cleft where the middle finger or toe should be. These split-hand/split-foot
malformations are rare limb deformities which can manifest in any
number of ways, including cases including only the thumb and one finger
(typically the little finger or little finger). It’s also associated with hearing loss.
Genetically speaking, it’s caused by several factors, including deletions,
translocations, and inversions in chromosome 7.
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A 2007 ABC article featured Bree Walker, a television anchorwoman living in
Los Angeles who lives with the disease. Walker also appeared on the
television show “Nip/Tuck” as a character with ectrodactyly who helps a
family with the disorder. Thankfully, surgical procedures can correct some of
these malformations.
8. Proteus Syndrome
In conjunction with neurofibromatosis type I, this is the disease that likely
afflicted Joseph Merrick, the so-called Elephant Man. It’s a condition in
which bones, skin, and other tissues are overgrown. Individuals
typically have organs and tissues that grow out of proportion with the rest of
their body, and because the overgrowth varies and exhibits no apparent
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order, it can result in strange and
imbalanced features. Signs of the
disorder don’t usually appear until about
6 to 18 months after birth. The severity of
proteus syndrome varies from individual
to individual, and it occurs in less than
one in one million people. And in fact,
only a few hundred documented cases
have ever been reported.
The disorder results from a mutation in
the AKT1 gene (which regulates cell
growth), causing mosaicism; as cells grow
and divide, some cells exhibit the
mutation while others do not. The
resulting mixture of normal and
abnormal cells is what causes the
overgrowth.
9. Trimethylaminuria
This genetic disorder is so rare that its rate of incidence is not even known.
But it’s very obvious when someone with trimethylaminuria is standing next
to you. Individuals with the condition, because they cannot break down the
naturally occurring — but pungent smelling — trimethylamine, literally
smell like rotting fish, rotting eggs, garbage, or urine. It’s for this
reason that it’s also called the Fish Odor Syndrome. Trimethylaminuria is
found in sweat, urine, exhaled breath, and other bodily secretions. But for
individuals with this disorder, typically women (for unknown reasons) it
shows up in abnormal amounts. The severity of the odors seem to peak just
before and during menstrual periods and after taking oral contraceptives;
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there may be a link to female sex hormones like progesterone or estrogen.
Consequently, people with trimethylaminuria have an exceptionally difficult
time in social settings. The odor can vary in intensity over time, but many
people experience depression and social isolation as a result.
10. Marfan Syndrome
While unusual in its manifestations, this
genetic disease is fairly common. Marfan
syndrome is a disorder of the connective
tissues, and it appears in about one in
every 10,000 to 20,000 births.
Interestingly, nearsightedness (or
myopia), is a common form of the
disease. But it’s more renowned for the
way it causes bones to overgrow and
create loose joints. People with Marfan Syndrome tend to have long and
thin arms and legs. Overgrown ribs can cause the chest bone to bend inward
or push outward. Spinal curvature is another problem.
It’s a myth, by the way, that Lincoln had it (he probably had Multiple
endocrine neoplasia type 2B). But other famous people with Marfan include
Sergei Rachmaninoff, Robert Johnson, and Bradford Cox of
Deerhunter/Atlas Sound fame (featured in image at left). Javier Botet, the
actor who recently spooked audiences as the bendy ghost in Mama, also has
Marfan syndrome.
Top illustration by appler via Shutterstock
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