What happens when
there is a chromosomal disorder?  According
to Oxford dictionaries, “a Trisomy is a condition in which an
extra copy of a chromosome is present in the cell nuclei, causing developmental
abnormalities.”  Trisomy usually manifest itself during
meiosis, which is upon the process of the eggs and sperm forming. In meiosis,
the duplicate chromosomes are arranged into daughter cells in two steps, called
meiosis I and meiosis II. Trisomy means that there are three copies of a
certain chromosome instead of the usual pair of chromosomes. Most people know of a prominent Trisomy, called Down syndrome,
however several types encircle human society today. In this paper the five
most common types of autosomal trisomies  in humans that survive to birth, otherwise
known as Trisomy 8, Trisomy 9, Trisomy 13, Trisomy 18, and Trisomy 21, will be
discussed in this following review.

First, there is Trisomy 8
mosaicism syndrome Trisomy 8 that according to Health line is a condition that
affects human chromosomes. People who have Trisomy 8 have three complete
copies, (instead of the typical two) of chromosome eight in their cells. The
extra chromosome eight appears in some of the cells, but not all. The symptoms
of this syndrome vary considerably, alternating from undetectable to, in some
cases, severe. The condition is also called Warkany syndrome 2.

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Trisomy 8 is a rare disorder,
affecting males more often than females at a ratio of 4-to-1, according to Health line. Trisomy 8 is
thought to occur in one out of every 25,000-50,000 pregnancies. The chances of
having more than one Trisomy 8 pregnancy are extremely low.

Trisomy 8 is caused by a problem
between the sperm and egg in which some cells do not divide accurately. Cells
do not divide simultaneously, so chromosomes are not distributed properly as a
result. This process is called “non-disjunction.” Depending on when the
non-disjunction occurs during the baby’s development, the organs and tissues
affected by extra chromosomes can differ. The condition is most commonly a accidental
incidence, but it is occasionally hereditary.

Symptoms of Trisomy 8 differ significantly.
Some children born with Trisomy 8 have severe, highly visible physical symptoms
while others show no visible symptoms. Potential symptoms include: longer-than-average
head, wide, deep eyes ,thick lips, large forehead, narrow shoulders ,long torso,
narrow pelvis ,deep creases on the hands and feet, problems with the palate or
mouth, joint problems and stiffness, spinal issues, such as scoliosis, kidney
problems, heart issue, bone and structure abnormalities, underdeveloped
genitals, lack of intellectual development, extreme stature (either very short
or very tall).

Sometimes Trisomy 8 does not
affect cerebral development. Intellectual development will be reliant, in many
ways, on the health of the child during crucial development stages. Other
symptoms of Trisomy 8 may cause an infant to have speech or learning delays.
But those delays are a result of the child’s physical limitations, not their
mental capabilities. Health line reports that often, children with Trisomy 8
may “catch up” to their peers in speech and learning. There are cases where
individuals with Trisomy 8 do not seem to have an intellectual impairment at
all.

This illness frequently goes
undiagnosed, because there may be no detectable symptoms. In cases where Trisomy
8 is suspected in an infant  the doctor
may take a blood or skin sample and perform a cell analysis. This test does not
define the severity of symptoms. Instead, it just describes whether Trisomy8 /”””””””””””””’is
present.

In most cases, a doctor diagnoses Trisomy
during pregnancy or early childhood. There are now blood tests that woman can
take during pregnancy to determine whether the baby they are carrying is likely
to have Trisomy 8. If the doctor notices that the baby is measuring small, has
only one artery in the umbilical cord, they will prescribe more testing for the
baby.

Although there is no cure for Trisomy
8, some symptoms of the condition may be treated. Treatment will contrast
depending on symptoms and severity. Symptoms with no associated health
problems, such as facial deformities, may be difficult to treat and may require
surgery. In some cases, heart surgery is also recommended. A surgeon can often
correct palate problems. This will help address any speech delay or impairment.

If most or all cells have the
extra chromosome, the condition is known as full or complete Trisomy 8. Full Trisomy
8 is fatal, often leading to miscarriage in the first trimester of pregnancy.

People with only some of the cells affected can
live normal lifespans, as long as other complications from the disorder do not
develop.

Second,
there is Trisomy 9, Mosaicism syndrome, is a chromosomal
disorder where some of the body’s cells have three copies of chromosome
9 (Trisomy), while other cells have the typical two
copies of this chromosome.  Most cases
are not inherited; it often occurs as a random event during the creation of the
reproductive cells (egg and sperm) or as the egg that was fertilized divides.

An error in cell
division (called nondisjunction) may cause some eggs or sperm to have an

irregular number
of chromosomes. If an egg or sperm with an additional chromosome 9 adds to the
genetic character of an embryo, the embryo will
have an extra copy of chromosome 9 in each cell.

In
infrequent cases, mosaic Trisomy 9 may be inherited from a parent with a chromosomal
rearrangement that occurs when a segment of chromosome 9 has broken off in two
places, rotated around 180 degrees and reinserted itself into the chromosome.
In these cases, the parent has a stable rearrangement, since the chromosome is
in a different order but no genetic material is gained or lost. Carriers of a
balanced rearrangement typically to not have any symptoms or health problems.

The
signs and symptoms of mosaic Trisomy 9 differ but may include: abnormal growth
including low birth weight, short stature, unusually small head, a sloping
forehead with narrow temples; a broad nose, a small jaw; cleft
lip and/or palate; low-set ears; unusually small eyes,
upwardly slanting eyelid folds.  Brain
malformations, mild to severe intellectual disability and developmental delay, congenital
heart defects, and vision problems, irregularities of the muscles and bones ,
undescended testes, and  kidney problems.

Sometimes
Trisomy 9 can be diagnosed before birth, by an ultrasound.  Other tests, such as chorionic villus sampling (CVS)
or an amniocentesis, fluid or tissue sample is used in order to get a picture
of the baby’s chromosomes. In other cases, the child is not diagnosed until
after birth through physical exam or a blood sample.

As
the embryo grows and divides, an attempt may be made to correct the mistake by
eliminating one extra chromosome 9. However, this attempt may be sometimes unsuccessful,
leaving some cells with an extra chromosome 9 and some cells with the extra
chromosome erased.  Children with bone or
muscle abnormalities or delayed motor milestones might be referred for physical
or occupational therapy.  Special
education classes can be given for intellectual disability. Heart defects
and cleft lip and/or palate
are usually surgically repaired.

The
prognosis for people with mosaic Trisomy 9 largely depends on the degree to
which the condition has affected any major organs, such as the heart and/or
brain. Some people affected by mosaic Trisomy 9, some of the body’s cells have
the usual two copies of chromosome 9, while other cells have three copies of Trisomy
9. The percentage of cells with Trisomy 9 and which parts of the body are
affected vary from person to person.

Third,
Trisomy 13, which is also called Patau syndrome, is a type of chromosome
disorder classified by having three copies of chromosome 13 in cells of the
body, instead of the usual two copies. In some affected people, only a portion
of cells contains the extra chromosome 13, which is called mosaic
Trisomy 13, while other cells contain the normal chromosome pair.         Mosaic Patau syndrome is not inherited.
In rare cases, the extra material can be attached to another chromosome, which
is called translocation. People with this disease usually have severe cerebral
incapacity and physical deformities in several parts of the body.

People
who have Trisomy 13 often have weak muscle
tone, heart defects, very small or poorly developed eyes, an opening in the
lip, with or without an opening in the roof of the mouth, brain or spinal cord
abnormalities, extra toes or fingers, and babies have trouble feeding or
digesting food. Babies often have low birth weight due to Trisomy 13.

Doctors
usually diagnose babies by fetal ultrasounds during the first trimester of a
pregnancy. There are many screening tests, such as cell-free DNA screening or
the pregnancy-associated plasma protein A. Other tests that are more certain
are a chorionic villus sampling or amniocentesis.

There
is no cure for Trisomy 13; however, doctors focus treatment on the patient’s
symptoms. Patients are given therapy and even surgery to correct abnormalities.
Each patient’s situation may vary.

Since
infants with this disease may have several life-threatening medical problems,
many infants with Trisomy 13 die within their
first days or weeks of life. Newborns that have this disease have to combat
pneumonia, seizures, congenital heart defects, and breathing difficulties.
According to WebMD, more than 80% of babies do not survive from this disease.
As a result, only five percent to 10 percent of children with this condition
live past their first year.

Another
type of Trisomy is Trisomy 18.  According
to WebMD, Trisomy 18 is also called Edwards syndrome, per the doctor who first
described this disease. Trisomy 18, like the other trisomies, has three copies
of extra chromosome. Instead of having a total of 46 chromosomes, number
eighteen is tripled. The extra chromosomes can come from either the father or
the mother of the fetus. Three types of Trisomy 18 are full Trisomy 18, partial
Trisomy 18, and mosaic Trisomy 18(either the extra chromosome is in all of the
cells, part of the cells or is in only some of the baby’s cells).

Symptoms
include: deformed feet, low-set ears, cleft palate, clenched fists with
overlapping fingers, and defects of the heart, lungs, kidneys and intestines.
There is also severe developmental delays, slowed growth. Newborns can have a
small head, small jaw, weak cry, and have problems with feedings.

In
order to diagnose, the doctor may check during pregnancy ultrasound.
Ultrasounds are not as accurate as other tests. Thus, the doctor may recommend
checking the cells by an amniocentesis or placenta (chorionic villus sampling).
Some parents may elect to have a chromosome blood test after giving birth which
would report the likelihood of having another baby with the same disorder.  The doctor may also recommend mothers to see a
genetic counselor. Treatment is aimed at correcting the symptoms with therapy
or surgery.

According
to Stanford Children’s Health, there are few reports stating that babies
survive to their teens with this disease, but it is rare. The majority of
babies born with Trisomy 18 die by their first birthday. A handful of patients
live well into their 20s and 30s.

            Moreover, Trisomy 21, also known as
Down syndrome, is the most common type of genetic disorders. Down syndrome was
discovered in 1866 and named after Dr. John Langdon, who first discovered it.
Just like the other trisomies, Trisomy 21 has three copies instead of the usual
pair. According to the National Down Syndrome Society, there are more than
350,000 people living with Down syndrome in the United States.

            There
are three types of Down syndrome and each have a different cause. First, there is
Trisomy 21, which causes most cases. When the egg and the sperm unite to form
the fertilized egg, three instead of two chromosomes 21 are present. As the
cells divide the extra chromosome is repeated in every cell. Next, there is
mosaic Trisomy 21, a rare form of Down syndrome, in which the extra chromosome
21 is present in some, but not all cells of the patient. Abnormal cell division
happens after fertilization. The third type is Translocation Trisomy 21, where
part of chromosome 21 becomes attached (translocated) to another chromosome
(usually the 13th, 14th or 15th chromosome). Translocation can happen before or
at conception.

            Symptoms
include slanting eyes, small mouth, short neck, flat face, low muscle tone.
People will also have small ears and below average intelligence. These symptoms
are for most people living with Down syndrome.

            To
diagnose Down syndrome, doctors use screening tests, diagnostic tests, and
blood test and physical exams. Sometimes they test both the mother and the
baby’s blood. The results for these diagnostic tests could take could take up
to 2 to 3 weeks.

            Treatment
for Down syndrome is aimed at the symptoms. Some children with Down syndrome
are provided physical and speech therapy. Adults that have Down syndrome are
offered occupational therapy in order to acquire skills to live on their own.
Counseling may be offered to help with emotional issues and blending into
society.

            In
the past people with Down syndrome mainly lived up to nine years old. According
to Medicine net, people with Down syndrome can now live up to 50 years and
more. Things have changed drastically for people living with Down syndrome.

            Even
though most people know of one Trisomy such as Down syndrome, we now know that
there are several. Each Trisomy has similarities and differences. Knowledge is
power. When we have more information on a disease then we can understand it
even more.

 

References