human genetic disorders
Post on 01-Jan-2016
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Autosomal Recessive Disorders
Requires the inheritance of two recessive alleles
Error found on chromosomes 1 - 22
Albinism
Inability to make melanin which gives pigmentation to hair, eyes, and skin
Mutation in the tyrosinase gene on chromosome #11
Tyrosinase is an enzyme that functions in the production of melanin
Problems
Visual Problems that cannot be corrected with glasses
Sunburn VERY easily Life expectancy is
normal
Cystic Fibrosis
Results in thick, sticky secretions in the respiration and digestive tract
Mutation in the gene for the transmembrane protein that acts as a channel for chloride ions
This gene is located on chromosome #7
Cystic Fibrosis
3,200 white babies born each year with CF
30,000 Americans live with CF 12 million Americans are carriers 1/20 European Americans are carriers
Cystic Fibrosis & Cholera
Cholera produces a toxin that opens chloride channels in the small intestine. This causes the often fatal diarrhea and dehydration in cholera patients.
In Europe, cholera epidemics have claimed millions of lives
People heterozygous for CF have fewer chloride channels and are resistant to cholera.
This explains the prevalence in European Americans
Phenylketonuria (PKU)
One of the most common causes of mental retardation
Mutation in gene for the enzyme phenylalanine hydroxylase on chromosome #12
This enzyme converts the amino acid phenylalanine to the amino acid tyrosine
Phenylketonuria (PKU)
If phenylalanine is not broken down, the build up of this amino acid causes brain dysfunction and mental retardation
All babies in the US are screen for PKU and if put on a phenylalanine restricted diet will not develop mental retardation.
1 in 4,500 people from Ireland have PKU 1 in 8,000 American Caucasians have PKU
Sickle Cell Anemia
A blood disorder that results in a change in shape of the red blood cell from round to “sickle” shaped. This causes clogging of capillaries and tissues are deprived of oxygen.
Mutation in the beta chain of the hemoglobin protein gene found on chromosome #11.
Sickle Cell Anemia
Most prevalent in persons of African descent.
1/12 African Americans are carriers of the disease.
Heterozygotes have protection from malaria.
Tay Sach’s Disease
A fatal disease that results from the build up of fatty acids around nerves of the central nervous system (brain & spinal cord)
Caused by the lack of the enzyme hexosaminidase A which is responsible for degrading lipids (fats)
The gene for this protein is located on chromosome #15
Problems
Babies appear normal at first. After a few months they develop developmental problems, go blind, deaf, and become paralyzed.
They are diagnosed by a “cherry-red” spot in the eye
They die by the age of five.
Prevalence
Tay-Sachs is most common in descendents of Central & Eastern European Jews
About 1/30 American Jews are carriers of Tay-Sachs disease
Autosomal Dominant Disorders
Require the inheritance of only one copy of the allele
Found on chromosomes 1 - 22
Achondroplasia
The most common form of dwarfism Caused by a mutation in the gene for
the Fibroblast growth factor receptor 3 protein
This protein functions in normal bone growth
This gene is found on chromosome #4
Achondroplasia
Because dwarfism was widely recorded in Egyptian art, it is considered the oldest recorded birth defect
1/25,000 births result in achondroplasia Over 80% of these births are to parents of
normal height; they are the result of a spontaneous mutation
Huntington’s Disease
Genetically programmed degeneration of brain cells causing uncontrolled movements, loss of mental faculties, and emotional disturbance
Caused by an abnormal gene for the protein huntingtin. Huntingtin is believed to function in normal brain activity.
The gene is located on chromosome #4.
Huntington’s Disease
In the normal gene for huntingtin, there is a section of DNA with up to 28 CAG codons repeated. (This codes for glutamine.)
In the abnormal gene, there is 40 or more repeats of the CAG codon and subsequently, a longer chain of glutamine in the protein.
Chains of glutamine are known for causing other neurological disorders.
Huntington’s Disease
Symptoms usually do not appear until a person is in their 40’s
There are currently 1,500 people in the US with Huntington’s Disease
It affects males and females and all races at the same rate
Marfan Syndrome
Characterized by problems with the skeleton, eyes, heart, and blood vessels.
Caused by a mutation in the gene for the protein fibrillin. This protein is essential for the formation of elastic fibers in the connective tissue.
This gene is located on chromosome #15.
Marfan Syndrome
People with Marfan characteristically are tall with very long limbs and fingers
It is believed that Abraham Lincoln had Marfan Syndrome
Many times people do not know they have the disease and yet are susceptible to aortic rupture
1/5,000 people in the US have Marfan Syndrome
Neurofibromatosis
Results in the growth of noncancerous tumors along nerves
Caused by a mutation in the gene for neurofibronin which is believed to act in tumor suppression. Therefore, if it is mutated, tumors are the result.
This gene is located on chromosome #17.
Neurofibromatosis
People afflicted have tumors that grow on their skin and can have bone deformity
1/4,000 babies in the US are born with neurofibromatosis
30 – 50% of the cases arise spontaneously
People usually lead a normal life
Osteogenesis Imperfecta
Characterized by bones that break frequently, often from no apparent cause
Results from abnormal production of collagen, the protein that is the primary constituent of the connective tissue (BOND IS A CONNECTIVE TISSUE!)
The gene for the alpha chain of collagen is located on chromosome #17, and the gene for the beta chain is on chromosome #7.
Osteogenesis Imperfecta
It is estimated there are 20,000 – 50,000 people in the US with OI
Many cases are the result of spontaneous mutations
The symptoms vary widely but with proper care, good diet, exercise, etc. people with OI can lead normal lives
X-Linked Recessive
Females have to inherit two copies of the gene
Males have to inherit one copy on the X from their mother
Duchenne Muscular Dystrophy
Characterized by progressive muscle weakness and wasting beginning early in life
Caused by a mutation in the gene for dystrophin
Dystrophin is the structural protein that provides support for muscle cells
No dystrophin—muscles do not work
Duchenne Muscular Dystrophy
1/3,500 boys worldwide have DMD
Most are wheelchair bound by 10 and die by age 20
Eventually cardiac and respiratory muscles waste away
Fragile X Syndrome
Most common cause of genetic mental impairment
Mutation in the Fragile X Mental retardation protein believed to help brain cells develop & function normally
Fragile X Syndrome
In the promoter region for the FMR1 gene, there are CGG repeats
In the normal gene there are 6 – 40 repeats In the abnormal gene there may be hundreds of
repeats The more CGG is repeated the more severe the
disease Heterozygous females make enough FMR to
have normal intelligence 1/2000 males have Fragile X; 1/4,000 females
Fragile X
Hemophilia
Disorder resulting in improper blood clotting from cuts or from internal injuries
It is a result of a mutation in the gene for Blood Clotting Factor VIII
This protein is involved in stopping the flow of blood out of vessels when they are ruptured
Hemophilia
About 18,000 people (almost all male) in the US have hemophilia
400 babies in the US each year are born with hemophilia
In the 1980’s approximately 10,000 children were infected with HIV because of transfusions for hemophilia
With proper treatment, hemophiliacs can live a normal life
Down Syndrome
Trisomy 21 Low muscle tone, flat face, slanted eyes,
abnormal shape and small size ears Most have congenital heart defects Suffer from mild to moderate mental retardation With good care, most live to around age 55 1/800 to 1/1,000 live births result in Down
Syndrome
Edward’s Syndrome
Trisomy 18 Results in small jaw, low-set ears, malformation
of the head, hands, feet; kidney and heart defects
30% of babies die in first month Less than 10% survive first year Occurs in 1/6,000 live births Twice as many females are born with Edward’s
as are males
Klinefelter’s Syndrome
XXY Men affected have enlarged breasts, small
testes, sparse facial and body hair, and inability to produce sperm
Some have lower IQ, many are very tall with long arms & legs
These men live as long as healthy individuals 1/500 – 1/1,000 males in US have XXY 3,000 males are born yearly with XXY
Patau Syndrome
Trisomy 13 Results in cleft palate, polydactyly, severe
mental deficiency, heart defects, and other abnormalities
Average lifespan is 3 days Only 1 in 20 children survive longer than 6
months Least common of all survivable trisomies Occurs in 1/8,000 – 1/12,000 births Birth rate favors females
Turner Syndrome
Monosomy X Inhibits sexual development and causes
infertility Females are usually short with webbed necks,
drooping eyelids, bone development problems, and retarded secondary sex characteristics
IQ is usually normal Occurs in 1/3,000 live births
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