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A very new and high technology for detection of
abnormal embryo is now available at our center ,
called Preimplantation Genetic Diagnosis ( PGD ).
Following ovarian stimulation , egg collection and
fertilization, embryos are cultured for another 2
days which they usually consist of 6-8 cells. Each
of these cells has complete genetic information and
also each cell has the potential to continue growth
to establish pregnancy. Therefore, one or two cells
can be removed from an 8-cells embryo by using an
embryo biopsy procedure and the embryo will continue
to develop normally. The removed cells will then be
analyzed by using a technique called Fluorescent in
situ Hybridization ( FISH ) or Polymerase Chain Reachion ( PCR ). The FISH technique can tell us
whether an embryo cell has two X chromosomes (
female ) or one X and one Y chromosome ( male ) and
FISH can also be used to detect specific chromosome
problems such as Down syndrome. FISH analysis can
give us the results within one day and the resulting
normal embryos will be transferred back into the
uterus.
This technique is now suitable for specific couples
such as advanced maternal age who have a very high
risk to have a child with Down syndrome , carriers
of genetic disease , recurrent abortion and couples
who carry X-linked diseases. Haemophilia and
Muscular dystrophy are examples of X-linked
diseases.
In the future it is likely that genetic testing of
embryos will be used more routinely to improve IVF
success rates as well as to prevent transmission of
genetic disease. With the transfer of genetically
normal embryos, a higher percentage of implantation
and reduced miscarriage rates can be expected.
For couples aware of genetic disorders through
family history or based on carrier testing, PGD
testing can be performed to help avoid a pregnancy
or child born with the specified genetic condition.
In genetic disorders where the gene structure is
known, such as Cystic Fibrosis or Tay-Sachs, the
actual genes of the embryo are examined for presence
of the condition. Other genetic disorders, such as
Duchenne muscular dystrophy or hemophilia, only
affect males and, therefore, the DNA of the embryo
is examined to determine the sex and only the female
embryos are transferred.
PGD can currently be used to detect the following
single gene disorders:
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Cystic Fibrosis is an
inherited disease that affects the respiratory
and digestive system. Caused by a defective gene,
cystic fibrosis affects the body's mucus and
sweat glands, often causing chronic lung
infections. It affects about one in 2500
Caucasians and one in 25 is a carrier of the
defective gene. It is the most common fatal
hereditary disorder affecting Caucasians in the
U.S. and requires both male and female carriers
to pass it on to children.
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Sickle Cell Anemia
is an inherited disease of the
red blood cells which can cause attacks of pain
and damage to vital organs and can lead to early
death. The disease occurs when a person inherits
two sickle cell genes or a combination of one
sickle cell gene and any one of several other
abnormal hemoglobin genes. In the U.S., most
cases of sickle cell disease occur among African-Americans,
and Hispanics of Caribbean ancestry. About one
in every 400 African-Americans has sickle cell
disease. It also affects people of Arabian,
Greek, Maltese, Italian, Sardinian, Turkish and
Indian ancestry.
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Thalassemia is a group of inherited diseases
of the blood, causing red blood cell
deficiencies. The most severe form, alpha
thalassemia, results in fetal or newborn death
and affects mainly individuals of Southeast Asia,
Chinese and Filipino ancestry. Others with
milder forms and varying degrees of anemia
appear healthy at birth and then slowly show
symptoms of the disease. About 100,000 babies
worldwide are born with severe forms of the
disease each year, most frequently occurring in
people of Italian, Greek, Middle Eastern,
Southern Asian and African ancestry.
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Tay Sachs Disease is a fatal inherited
disease of the central nervous system where
affected babies lack the necessary protein for
breaking down certain fatty substances in brain
and nerve cells. These substances build up and
gradually destroy brain and nerve cells, until
the entire central nervous systems shuts down,
causing the child to go blind, become paralyzed
and die by age 5. Tay Sachs occurs most
frequently in descendants of Central and Eastern
European Jews. About one out of every 30
American Jews carries the gene. Non-Jewish
individuals of French-Canadian ancestry and
member of the Cajun population in Louisiana are
similarly at risk - about 100 times the rate of
occurrence of other ethnic groups.
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Myotonic Dystrophy
shows up in people at various stages of life
and can cause mild or severe symptoms affecting
various types of tissues and organs. It affects
about one in 8000 people and includes 4
different types: congenital (appearing at birth
and is most severe); juvenile (appearing after
birth and in teen years); adult (appears in late
20's to early 40's); and late onset (appears
later after 40's and is generally mild).
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Fragile X Syndrome is a hereditary condition
which can cause learning problems in both males
and females.
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Phenylketonuria (PKU) is a rare, inherited
metabolic disease that results in mental
retardation and other neurological problems when
treatment is not started within the first few
weeks of life.
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Gaucher's Disease is a
lipid-storage disorder commonly affecting Jewish
people of Eastern European ancestry that causes
symptoms ranging from none to severe disability
and death.
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Retinoblastoma
is an intraocular (eye) cancer of childhood
that affects approximately 300 children in the
U.S. each year, causing many to lose their
affected eye(s).
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Hemophilia A & B are
genetic disorders of the blood leading to
improper clotting, causing patients to suffer
from frequent spontaneous bleeding episodes.
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Fanconi Anemia is an inherited anemia that
leads to bone marrow failure and affects males
and females of all ethnic groups.
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Alzheimer’s (APP gene) is an incurable
neurological disease in which changes of the
nerve cells of the brain result in the death of
large numbers of cells, causing serious mental
deterioration, dementia and death.
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Retinitis Pigmentosa is a progressive
degeneration of the retina that affects night
vision and peripheral vision and may lead to
blindness.
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Epidermolysis Bullosa, a
group of inherited disorders in which massive
blistering of the skin develops in response to
minor trauma, varies in severity from minor
blistering to a lethal form in which the
constant massive blistering and scarring
ultimately lead to death.
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Duchenne's muscular dystrophy, characterized
by rapidly progressive muscle weakness of the
legs and pelvis and later affecting the whole
body, usually appears in males 1 to 6 years old.
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P53 Oncogene Mutation occurs with unusually
high frequency in tumor tissue. The gene, called
P53, mutates in nearly half of all cancers.
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HLA Genotyping
involves the exploration of generic information
encoded on white blood cells, searching for
potentially fatal blood diseases.
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OTC Deficiency, in its most common form,
causes death in affected newborn males because
of their inability to properly process nitrogen
in food proteins due to a genetic defect of the
liver.
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Neurofibromatosis (NF1 & NF2) is a genetic
disorder of the nervous system that causes
tumors to form on the nerves anywhere in the
body at any time.
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Multiple Epiphyseal Dysplasia, also called
Fairbank's Disease, is an inherited condition
resulting in the formation of abnormal epiphyses
or bone ends.
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Achondroplasis, or dwarfism, is an inherited
condition that is caused by a lack of growth
spurt, particularly in the arms and legs at the
time of puberty.
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LCHAD is caused by an enzyme defect in the
beta-oxidation cycle, resulting in an inability
to break down fatty acids into a useable energy
source, ultimately causing low blood sugar
levels, poor muscle tone, and problems with the
functioning of the heart.
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X-Linked Hydrocephalus, transmitted by
females and manifested in males, is a
disturbance of formation, flow or absorption of
cerebrospinal fluid that leads to an increase in
volume occupied by this fluid in the central
nervous system.
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ADA Deficiency, while very rare and often
lethal, results in improper functioning of the
body's immune system and often causes those
afflicted to live in sheltered or enclosed
environments.
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