Goal 3 - Genetic Disorders
Goal 3 - Genetic Disorders Pages 312, 314, 323, 327, 329
Sickle Cell Anemia
Sickle Cell Anemia
- Autosomal recessive gene
- Cause = point mutation (base substitution) in gene for hemoglobin.
- Results = blood cells have a deformed, sickle shape. They get caught in blood vessels and restrict blood flow to tissue causing damage, pain, and possibly death. They break leading to a lower red blood cell count.
- Symptoms = fatigue, headaches, muscle cramps, kidney and heart damage.
- Occurs most in = people of tropical African descent.
- Heterzygotes have some normal and some sickle red blood cells. They are at a lowered risk for malaria (deadly tropical disease) because of this condition. Up to 45% of central African population is a heterozygote. With medical treatment suffers can live a normal life.
Cystic Fibrosis
- Cause = mutation in gene for the transport protein (plasma/cell membrane)responsible for transporting chloride ions
- Result = misshapen transport protein in cells of digestive tract and respiratory system, mucus accumulation in lungs and pancreas.
- Symptoms = difficulty breathing and digesting food, many lung infections.
- Occurs most in = white Americans; 1 in 2,000 has cystic fibrosis.
- Treatment = drug therapy, special diets, new gene therapy. Treatment has raised the life expectancy of those with Cystic Fibrosis past childhood.
- Death usually 40’s to 50’s.
- Cystic Fibrosis - Autosomal recessive gene.
PKU
- If a child is homozygous for PKU - it appears healthy at first because mom’s normal enzyme level prevented the PKU accumulation during development. Once child begins drinking milk, (which is rich in PKU), the amino acid accumulates and mental retardation occurs.
- Testing = today all infants are tested after birth.
- Treatment = if detected infants given a special diet low in PKU until the brain fully develops. Pregnant women who are homozygous recessive for PKU must limit it during pregnancy because high levels in her blood may damage fetus.
- PKU = Autosomal recessive
- Cause = Absence of enzyme that converts one amino acid, phenylalanine, to a different amino acid tyrosine.
- Result = Can not break down phenylalanine (milk)
- Symptoms = Damage to the central nervous system, mental retardation
- Occur most in = people whose ancestors are from Norway, Sweden, or Ireland.
Tay Sachs
- Tay Sachs = Autosomal Recessive.
- Cause = the enzyme needed to break down gangliosides (fatty substances needed for the proper development of the brain and nerve cells) is missing. As a result, gangliosides continue to build up in the brain. When the brain becomes clogged with this fatty material it is no longer able to function normally.
- Symptoms = Brain and Nervious system deteriorates.
- Result = Death before adulthood.
- Most Common in = Jewish people of eastern European and Russian origin, sometimes referred to as Ashkenazi Jews, French-Canadian and Cajun French families.
Hemophilia
- Hemophilia - X-linked recessive gene.
- Cause = mutation in gene builds a defective forms of a protein needed to clot blood.
- Result = blood does not clot.
- Symptoms = difficulty in healing, bleeding without stoping, internal bleeding, lots of brusing, arthritis (long term).
- Occurs most in = males.
- Men have the disease if have one recessive gene since they have only one X chomosome. Women must have two recessive copies in order to have this disorder since they have two copies of the X chromosome.
Other Sex-Linked Disorders
Colorblindness (Red - Green)
Muscular Dystrophy
- Colorblindness (Red/Green) - X-linked recessive gene.
- Can’t see reds or greens
Muscular Dystrophy
- Muscular Dystrophy = X-linked recessive gene.
- Muscles waste away and eventually stop working.
Turner's Syndrome
Turner’s Syndrome
- Turner’s Syndrome = Sex linked (non-disjunction)
- Missing an X Chromosome
- Female is XO
- Symptoms = Short stature, (swelling) of the hands and feet, Broad chest (shield chest) and widely-spaced nipples, Low hairline, Low-set ears, Reproductive sterility, Crude ovaries, absence of a menstrual period, Increased weight, obesity, Shield shaped thorax of heart, Small fingernails, Webbing of the neck, Poor Breast Development or Horseshoe kidney.
Klinefelter's Syndrome
Klinefelter’s Syndrome
- Klinefelter’s Syndrome - Sex Linked (non-disjunction)
- Extra Y chromosome in males
- Male is XYY
- Symptoms = sterile, small testicles, a lanky, youthful build and facial appearance, rounded body type, increased breast tissue, small penis.
Triple X Syndrome
Triple X
- Triple X = Sex Linked (non-disjunction)
- Extra X chromosome in females
- Female is XXX
- Symptoms = taller than average, increased risk of learning disabilities, delayed speech and language skills, developmental delays and behavioral problems are also possible, but these characteristics vary widely among affected girls and women. Most females with triple X syndrome have normal sexual development and are able to conceive children.
Huntington's Disease
Huntington’s Disease
- Huntington’s Disease = autosomal dominant gene.
- Cause = rare dominant allele
- Results = breakdown of certain areas of the brain and central nervous system.
- Symptoms = deterioration of the central nervous system (the brain), jerky movements, mental deterioration. This is a lethal allele - its KILLS those who have it!
- This disorder does not appear until the individual is between the ages of 30 to 50. Since it is a dominant gene and kills those who have it, it would normally be removed from the population (How can it stick around if it kills everyone who has it?). But by the time the disorder appears, individual have already reproduced and passed on the gene.
- There is a genetic test developed for Huntington’s Disease. This helps individuals with the disorder decide if they will have children.
Down's Syndrome
Down’s Syndrome
- Down’s Syndrome = Chromosomal mutation.
- Cause = 3 copies of chromosome 21. This result from non-disjunction - when the homologous chromosomes fail to separate during meiosis.
- Results and Symptoms = some mental retardation, short stature, broad nose, extra folds on the upper eye lids.
- Higher occurrence in mothers over 40, about 1 in 16 instead of 1 in 1,000.
How to detect genetic disorders
Karyotypes
Chromosomal mutations can be detected by making a karyotype (a chart of chromosome pairs). There are two techniques used to detect karyotype of a fetus during pregnancy.
Amniocentesis - remove small amount of fluid surrounding the fetus and fetal cells in it.
Chorionic villi sampling - remove tiny piece of embryonic membrane.
How can we detect mutations?
Gene mutations can sometimes be detected by the use of DNA fingerprinting.
Chromosomal mutations can be detected by making a karyotype (a chart of chromosome pairs). There are two techniques used to detect karyotype of a fetus during pregnancy.
Amniocentesis - remove small amount of fluid surrounding the fetus and fetal cells in it.
Chorionic villi sampling - remove tiny piece of embryonic membrane.
How can we detect mutations?
Gene mutations can sometimes be detected by the use of DNA fingerprinting.
Others.....
Other Diseases
–Diabetes
–Cancer
–Asthma
Environmental Causes of Disorders
–Lead poisoning
- Some diseases are affected by environmental factors as well as genetic factors.
- Environmental factors include radiation and tobacco smoke.
- Examples
–Diabetes
–Cancer
–Asthma
Environmental Causes of Disorders
- Some diseases/disorders are mainly environmental
- Examples
–Lead poisoning