Transcript Genetic Disorders

Genetic Disorders
G. Crotts
Spring 07
Down Syndrome
• Results from nondisjunction where a gamete has
an extra or missing chromosome
• Nondisjunction
• Also called Trisomy-21
• Affects 1 in 691 babies born in the U.S.
• Cause of nondisjunction occurring is unknown.
• Woman age 35 and older have a significantly
higher risk of having a child with the condition.
Age 30---1 in 1,000 chance
Age 35---1 in 400 chance
Age 42---1 in 60 chance
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All children tend to share certain physical features,
regardless of race.
These include:
-flat facial profile
-slant to eyes
-single crease across center of palms
-enlarged tongue
-typically smaller stature
Generally have mental disabilities that range from
mild to severe.
Heart problems and other medical problems can be
common.
Can be detected before birth using a karyotype
http://www.kidshealth.org/parent/medical/genetic/down_syndrome.html
Karyotype of Person with Down Syndrome
Triple X Syndrome
(XXX or Trisomony X)
• Females may be slightly taller
• Increased risk of learning disabilities, delayed
speech and language skills
• 1/1,000 newborn girls
• It’s not inherited
Karyotype of Person with Triple XXX
Turner Syndrome XO
• Females missing a sex chromosome
• 1 in 2000 females
• In infants: swollen hands and feet, wide webbed
neck
• In adults: drooping eyelids, incomplete
development during puberty, short height, no
periods, infertility
• Growth hormones for height
• Can lead to complications
Turner Syndrome
Karyotype of Person with XO
XXY-Klinefelter Syndrome
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Males have an extra X chromosome
Affects 1 in 500 to 1000 males
Causes infertility
Abnormal body proportions
May prescribe testosterone
Karyotype of Person with XXY
XYY Syndrome
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Males have an extra Y chromosome
No unusual physical features
No medical problems
Learning disabilities
Behavioral problems
1/1,000 newborn boys
Karyotype of Person with XYY
Huntington’s Disease
• Autosomal dominant trait- not on sex chromosomes,
but on chromosome 4.
• 1/10,000 people. More prevalent in Caucasians.
• A person with Huntington’s may not know they have
it until they are 30-50 years old. By that time they
could have already passed it on to their children.
• Too much of a particular protein is produced and it
causes the brain to deteriorate and then leads to an
early death.
• No cure
• The gene on chromosome number 4 contains too
many repeats of the nucleotide sequence CAG. A
normal person would have an average of 19 with the
highest being 34, but a person with Huntington’s
disease would have more than 40.
• So the gene codes for too much of a protein
called
http://www.hdsa.org
Huntington Video
http://www.about-dementia.com/images/dementia/HuntingtonsPedigree.gif
Sickle Cell Anemia
• Autosomal recessive
• 1/1,500 African Americans
• More than 70,000 Americans have sickle cell anemia.
And about 2 million Americans - and one in 12
African Americans - have sickle cell trait (this means
they carry one gene for the disease, but do not have
the disease itself).
• Affects a protein in red blood cells called
hemoglobin, which carries oxygen.
• Sickled cells can block blood vessels and the
movement of blood and oxygen to body parts.
Sickle Cell Anemia
http://medicine.osu.edu/lend/Portfolios/0506/AR%20Port/files/SICKLE%20CELL%20WEBSITE/images/sc2.jpg
Cystic Fibrosis
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Autosomal recessive
1/ 2,080 Caucasians
Mucus clogs lungs, liver, and pancreas
30,000 people in US have been diagnosed.
Mutations in a gene on chromosome 7.
Scientists don't know exactly why the CF gene evolved in
humans, but they have some evidence to show that it helped
to protect earlier generations from the bacteria that causes
cholera, a severe intestinal infection.
• One of the newest treatments for CF that's still being
researched is an inhaled spray containing normal copies of the
CF gene. These normal genes deliver the correct copy of the
CF gene into the lungs of CF patients.
http://www.supplementnews.org/images/Cystic%20Fibrosis.jpg
Tay-Sachs Disease
• Autosomal Recessive
• 1/1,600 Ashkenazi Jews
• Enzymes clear out fatty proteins that interfere with our
growth. Because these enzymes get rid of these proteins we
are able to develop hearing, vision, and movement.
• A baby with Tay-Sachs disease is born without one of those
important enzymes, called Hexosaminidase A (Hex A). So, as
those fatty proteins build up in the brain, they hurt the baby's
sight, hearing, movement, and mental development.
• A baby born with Tay-Sachs develops normally in the first 3 to
6 months of life. During the next months - or even years - the
baby will progressively lose the ability to see, hear, and move.
A red spot will develop in the back of the child's eyes. The
child will stop smiling, crawling, turning over, and reaching out
for things. By the age of 2, the child may have seizures and
become completely disabled. Death usually occurs by the
time the child is 5 years old.
http://www.kidshealth.org/parent/medical/genetic/tay_sachs.html
Phenylketonuria
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Autosomal Recessive
1/18,000
Abbreviated PKU.
Newborns are given a test soon after they are born.
A genetic disorder that is characterized by an inability of the
body to utilize the essential amino acid, phenylalanine. The
body can’t break it down. It builds up in the person’s blood
and body tissues. If untreated causes mental disabilities and
death.
• Controlled by a very low phenylalanine diet.
• High protein foods, such as: meat, fish, poultry, eggs, cheese,
milk, dried beans, and peas are avoided. Instead, measured
amounts of cereals, starches, fruits, and vegetables, along
with a milk substitute are usually recommended.
http://www.medhelp.org/lib/pku.htm
Hemophilia
• Sex-linked or X-linked trait
• Blood does not clot. Bruises and cuts are problematic, but
internal bleeding can be fatal.
• Males are much more likely to have the disease, while
females are carriers.
• 1/7,000 people
• Treated with a Clotting Factor Replacement Therapy.
• If internal bleeding occurs, doctors can replace the missing
clotting factor immediately. People with the disorder are
trained in recognizing when they are bleeding internally.
http://www.nhlbi.nih.gov/health/dci/Diseases/hemophilia/hemophilia_causes.html
http://web.nmsu.edu/~gene305/hemophilia.jpg
Muscular Dystrophy
• Sex-linked or X-linked
• Wasting away of muscles---including heart and lungs.
Body is missing the genes to make the proteins that
strengthen and maintain muscles.
• Shortened life expectancy.
• 1/10,000
• Physical Therapy and Breathing treatments are used
to assist people with this disorder as well as assistive
technological devices.
http://www.kidshealth.org/parent/medical/bones/muscular_dystrophy.htm
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