GENETIC DISORDERS Causes, Symptoms and Treatments
Nondisjunction – a problem with meiosis <ul><li>A “junction” is a place of meeting or joining. </li></ul><ul><li>So, to “d...
Nondisjunction results in sex cells with either an extra or missing a chromosome
Nondisjunction disorders <ul><li>During fertilization, a “normal” sex cell is joined with a sex cell that has either an ex...
The Karyotype…
Trisomies with the sex chromosomes <ul><li>Klinefelter syndrome:  47, XXY  males. Male sex organs; unusually small testes,...
<ul><li>Trisomy X: 47, XXX  females. 1:1000 live births - healthy and fertile - usually cannot be distinguished from norma...
Trisomies in Autosomes (there are only three that will survive beyond birth) <ul><li>Patau syndrome (trisomy 13) :  seriou...
Down’s syndrome <ul><li>Down syndrome (trisomy 21): The result of an extra copy of chromosome 21. People with Down syndrom...
Maternal age is an important factor…
Other genetic disorders – symptoms, how inherited, and treatments <ul><li>Sickle Cell Anemia  – this genetic disorder is a...
Symptoms and treatments <ul><li>Sickle Cell Anemia shows an example of  pleiotropy.   </li></ul><ul><li>There are several ...
Heterozygote Advantage <ul><li>This is due to the fact that the  heterozygote (carrier) has an increased resistance to mal...
Tay Sach’s Disease <ul><li>Tay Sach’s Disease  – this disorder is also autosomal homozygous recessive. A baby with Tay Sac...
Symptoms and treatments <ul><li>This disease is caused by the absence of an important enzyme.  </li></ul><ul><li>The baby ...
Cystic Fibrosis <ul><li>Cystic Fibrosis  – this disorder is autosomal homozygous recessive. A person with Cystic Fibrosis ...
Symptoms and treatments <ul><li>The primary symptoms of CF are an increased production of mucus in the lungs and thickened...
Heterozygote advantage <ul><li>Cystic fibrosis is most common in Caucasians (whites) whose ancestors can be traced back to...
Phenylketonuria (PKU) <ul><li>This disorder is autosomal homozygous recessive. (Can you guess the inheritance pattern?). T...
Symptoms and  Treatments <ul><li>If untreated, the person with PKU will  </li></ul><ul><li>have progressive nervous system...
Hemophilia <ul><li>This disorder is caused by a sex-linked recessive gene. It has the same inheritance pattern as colorbli...
Symptoms and Treatments <ul><li>Symptoms of hemophilia include excessive bleeding from open wounds or bruises. The conditi...
Huntington’s Disease <ul><li>This disease has an unusual inheritance pattern for a genetic disorder. It is caused by an au...
Symptoms and Treatments <ul><li>The reason that the disorder persists in the population is that, in most cases, its onset ...
Prenatal testing <ul><li>This procedure involves the insertion of a long needle into the woman’s abdomen and the removal o...
Prenatal testing <ul><li>This procedure is done between the 10 th  and 12 th  week of pregnancy and involves the removal o...
Many disorders that can be determined with prenatal testing. <ul><li>Achondroplasia </li></ul><ul><li>Huntington disease <...
For more information… <ul><li>http://www.biology.iupui.edu/biocourses/N100/2k2humancsomaldisorders.html   </li></ul><ul><l...
More references… <ul><li>http://www.ninds.nih.gov/disorders/taysachs/taysachs.htm   </li></ul><ul><li>http://www.pkunews.o...
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Genetic disorders

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Genetic disorders

  1. 1. GENETIC DISORDERS Causes, Symptoms and Treatments
  2. 2. Nondisjunction – a problem with meiosis <ul><li>A “junction” is a place of meeting or joining. </li></ul><ul><li>So, to “disjunct” is to unjoin – or separate… </li></ul><ul><li>During which phase of meiosis do the chromosomes separate? </li></ul><ul><li>Anaphase I and </li></ul><ul><li>Anaphase II </li></ul><ul><li>So nondisjuction indicates that the chromosomes (or chromatids) do not separate as they should… </li></ul>
  3. 3. Nondisjunction results in sex cells with either an extra or missing a chromosome
  4. 4. Nondisjunction disorders <ul><li>During fertilization, a “normal” sex cell is joined with a sex cell that has either an extra or is missing a chromosome. </li></ul><ul><li>The chromosome involved will determine the disorder. </li></ul><ul><li>Larger chromosomes involved with nondisjunction will often result in miscarriage. </li></ul>
  5. 5. The Karyotype…
  6. 6. Trisomies with the sex chromosomes <ul><li>Klinefelter syndrome: 47, XXY males. Male sex organs; unusually small testes, sterile. Breast enlargement and other feminine body characteristics. Normal intelligence. </li></ul><ul><li>47, XYY males : Individuals are somewhat taller than average and often have below normal intelligence. At one time (~1970s), it was thought that these men were likely to be criminally aggressive, but this hypothesis has been disproven over time. </li></ul>
  7. 7. <ul><li>Trisomy X: 47, XXX females. 1:1000 live births - healthy and fertile - usually cannot be distinguished from normal female except by karyotype </li></ul><ul><li>Monosomy X (Turner's syndrome) : 1:5000 live births; the only viable monosomy in humans - women with Turner's have only 45 chromosomes!!! XO individuals are genetically female, however, they do not mature sexually during puberty and are sterile. Short stature and normal intelligence. (98% of these fetuses die before birth) </li></ul>
  8. 8. Trisomies in Autosomes (there are only three that will survive beyond birth) <ul><li>Patau syndrome (trisomy 13) : serious eye, brain, circulatory defects as well as cleft palate. 1:5000 live births. Children rarely live more than a few months. </li></ul><ul><li>Edward's syndrome (trisomy 18) : almost every organ system affected 1:10,000 live births. Children with full Trisomy 18 generally do not live more than a few months. </li></ul>
  9. 9. Down’s syndrome <ul><li>Down syndrome (trisomy 21): The result of an extra copy of chromosome 21. People with Down syndrome are 47, 21+. Down syndrome affects 1:700 children and alters the child's phenotype either moderately or severely: </li></ul><ul><li>characteristic facial features, short stature; heart defects </li></ul><ul><li>susceptibility to respiratory disease, shorter lifespan </li></ul><ul><li>prone to developing early Alzheimer's and leukemia </li></ul><ul><li>often sexually underdeveloped and sterile, usually some degree of mental retardation. </li></ul><ul><li>Down Syndrome is correlated with age of mother but can also be the result of nondisjunction of the father's chromosome 21. </li></ul>
  10. 10. Maternal age is an important factor…
  11. 11. Other genetic disorders – symptoms, how inherited, and treatments <ul><li>Sickle Cell Anemia – this genetic disorder is autosomal homozygous recessive (ss). </li></ul><ul><li>Autosomal means that it is NOT a gene on the sex chromosomes and so males and females will have equal inheritance. </li></ul><ul><li>Homozygous recessive means that the person will have two recessive genes. This person must inherit a recessive gene from both the mother and the father. (Both the mother and father would be heterozygous). </li></ul><ul><li>  Ss X Ss </li></ul><ul><li>Two heterozygous parents would have a 1 in 4 (25%) chance of having a child with Sickle Cell Anemia. </li></ul>S s S SS Ss s Ss ss
  12. 12. Symptoms and treatments <ul><li>Sickle Cell Anemia shows an example of pleiotropy. </li></ul><ul><li>There are several phenotypes or traits associated with one gene. </li></ul>There is no cure at this time, and treatments depend on the symptoms. Oxygen therapy and rest are advised.
  13. 13. Heterozygote Advantage <ul><li>This is due to the fact that the heterozygote (carrier) has an increased resistance to malaria. If you follow the family history of the people that are carriers back in time, most likely their ancestors are from central Africa where malaria was a problem hundreds of years ago. The carriers were more likely to have survived malaria and passed their genes on to their offspring. This has kept this gene in the population. </li></ul><ul><li>Sickle cell anemia is more common in African Americans </li></ul><ul><li>The heterozygote has survival advantage. </li></ul>
  14. 14. Tay Sach’s Disease <ul><li>Tay Sach’s Disease – this disorder is also autosomal homozygous recessive. A baby with Tay Sach’s would have to inherit a recessive gene from each parent. </li></ul><ul><li>Tt X Tt </li></ul><ul><li>Again, there is a 25% chance of these two parents having a child with Tay Sach’s disease. </li></ul>T t T TT Tt t Tt tt
  15. 15. Symptoms and treatments <ul><li>This disease is caused by the absence of an important enzyme. </li></ul><ul><li>The baby is born normal and commonly develops normally until about 6 months of age. </li></ul><ul><li>Early symptoms include loss of peripheral vision. This progresses to seizures, loss of muscle control, loss of mental functions, blindness and finally death. A child with Tay Sach’s will commonly die by the age of five. </li></ul><ul><li>The only treatment is treatment of the symptoms. There is no cure. </li></ul><ul><li>This disorder is most common in people of Eastern European Jewish descent. Again, the heterozygote (carrier) has resistance to tuberculosis. If you would follow the people that carry this gene back in their familial lineage, their ancestors would have most likely survived tuberculosis during an outbreak hundreds of years ago. </li></ul>
  16. 16. Cystic Fibrosis <ul><li>Cystic Fibrosis – this disorder is autosomal homozygous recessive. A person with Cystic Fibrosis had to have inherited a recessive gene from each parent. Both parents would be carriers. (heterozygous). </li></ul><ul><li>Cc X Cc </li></ul><ul><li>Again, there is a one in four chance of having a child with Cystic Fibrosis. </li></ul>C c C CC Cc c Cc cc
  17. 17. Symptoms and treatments <ul><li>The primary symptoms of CF are an increased production of mucus in the lungs and thickened body fluids elsewhere (pancreatic fluids, etc.) There are several secondary problems that can arise. </li></ul><ul><li>Treatments include physical therapy to clear the lungs of excess mucus, suction and treatments for secondary problems (diabetes, infections, etc.) </li></ul><ul><li>While there is no cure at this time, CF is a disease that has been studied for over 10 years for gene therapy . The premise is to take the correct gene and insert it into a cold virus, which should insert this gene into the cells of the respiratory system. This has not perfected at this time – but it is an exciting possibility for the near future. </li></ul>
  18. 18. Heterozygote advantage <ul><li>Cystic fibrosis is most common in Caucasians (whites) whose ancestors can be traced back to western Europe. As with the disease discussed above, the heterozygote (carrier) has resistance to a disease. In this case, it is Cholera. Cholera depletes the system of fluid very rapidly and having slightly thicker body fluids is an advantage in surviving Cholera. </li></ul>
  19. 19. Phenylketonuria (PKU) <ul><li>This disorder is autosomal homozygous recessive. (Can you guess the inheritance pattern?). The person would receive a recessive gene from each parent. Commonly, both parents would be heterozygous and would have a one in four chance of having a child with PKU. </li></ul><ul><li>Pp X Pp </li></ul>P p P PP Pp p Pp pp
  20. 20. Symptoms and Treatments <ul><li>If untreated, the person with PKU will </li></ul><ul><li>have progressive nervous system </li></ul><ul><li>damage and will have a degree of retardation. </li></ul><ul><li>There is an effective treatment for PKU. Diet modification to greatly reduce the amount of the amino acid, phenylalanine, can allow these individuals to have long, healthy lives. </li></ul><ul><li>PKU is not associated with any particular ethnic group. It is relatively rare – about 1 in 15,000 births will have PKU. Because affected individuals can live long lives and reproduce, this gene should become more common in the future. </li></ul>
  21. 21. Hemophilia <ul><li>This disorder is caused by a sex-linked recessive gene. It has the same inheritance pattern as colorblindness. Males will have this disorder if they inherit the gene from only one parent (the mother). Females would have to receive this gene from both parents. </li></ul><ul><li>X H X h x X H Y </li></ul><ul><li>Neither parent has hemophilia, but the mother is a carrier (heterozygous). </li></ul><ul><li>With a carrier mother and a normal father, the daughters have a 50% chance of being a carrier, but will NOT have hemophilia. The sons have a 50% chance of having hemophilia. </li></ul>X H X h X H X H X H X H X h Y X H Y X h Y
  22. 22. Symptoms and Treatments <ul><li>Symptoms of hemophilia include excessive bleeding from open wounds or bruises. The condition is caused by the lack of a blood-clotting factor. Complications that may arise include joint problems. </li></ul><ul><li>Treatments of hemophilia include use of clotting factors which can be used as a preventative for bleeding or when bleeding occurs. Treatments are much better than in the past and if careful, it is possible for hemophiliacs to participate in sports. </li></ul><ul><li>Gene therapy is under study for future treatments. </li></ul>
  23. 23. Huntington’s Disease <ul><li>This disease has an unusual inheritance pattern for a genetic disorder. It is caused by an autosomal dominant gene. </li></ul><ul><li>What this means is that any person that develops Huntington’s disease will have a parent that has had this disorder. </li></ul><ul><li>Hh X hh </li></ul><ul><li>All children of a person with Huntington’s have a 50% chance of developing this disorder. </li></ul>H h h Hh hh h Hh hh
  24. 24. Symptoms and Treatments <ul><li>The reason that the disorder persists in the population is that, in most cases, its onset is after the reproductive years (age 30-50). A person will have already had their children before they know if they will have the disease and in turn, have the possibility of passing it to their children. </li></ul><ul><li>The symptoms of Huntington’s Disease include progressive chorea (shaking and jerking movements) and degenerative neurological problems. </li></ul><ul><li>Early symptoms include clumsiness, depression, forgetfulness (tell me if you have never had a day when you couldn’t find your car keys, tripped on the carpet and felt a little blue – for people that have this disorder in their family, a day like this has a whole different outlook). </li></ul><ul><li>There is no cure and treatments include treating the symptoms. Commonly the disease is slow acting with 10 – 30 years between onset of symptoms and death. </li></ul><ul><li>  </li></ul>
  25. 25. Prenatal testing <ul><li>This procedure involves the insertion of a long needle into the woman’s abdomen and the removal of a small amount of amniotic fluid (about 2 teaspoons). </li></ul><ul><li>This test is done after the 15 th week of pregnancy and the location of the fetus is monitored with ultrasound. </li></ul><ul><li>This is a relatively safe test, but does carry about a 1 in 200 risk of miscarriage. </li></ul><ul><li>The test is not done on all pregnant women – only those that carry a higher risk of genetic abnormalities (those with genetic disorders in their family history or women over 35). </li></ul><ul><li>Amniocentesis </li></ul><ul><li>Amniocentesis </li></ul>
  26. 26. Prenatal testing <ul><li>This procedure is done between the 10 th and 12 th week of pregnancy and involves the removal of a small amount of the placenta. </li></ul><ul><li>This can be done either with the insertion of a needle through the abdomen or with a catheter inserted through the vagina and cervix. </li></ul><ul><li>There is a slightly higher risk of miscarriage with this procedure than with amniocentesis. </li></ul><ul><li>Chorionic Villi Sampling </li></ul><ul><li>CVS </li></ul>
  27. 27. Many disorders that can be determined with prenatal testing. <ul><li>Achondroplasia </li></ul><ul><li>Huntington disease </li></ul><ul><li>Cystic fibrosis </li></ul><ul><li>Sickle cell disease </li></ul><ul><li>Tay-Sachs disease </li></ul><ul><li>Beta-thalassemia </li></ul><ul><li>Chromosomal disorders such as Down’s syndrome </li></ul><ul><li>Spina bifida </li></ul><ul><li>Anencephaly </li></ul><ul><li>http://kidshealth.org/parent/system/medical/prenatal_tests.html </li></ul>
  28. 28. For more information… <ul><li>http://www.biology.iupui.edu/biocourses/N100/2k2humancsomaldisorders.html </li></ul><ul><li>http://trc.ucdavis.edu/biosci10v/bis10v/week4/08chromosomenumber.html </li></ul><ul><li>http://www.biology.iupui.edu/biocourses/N100/2K2humancsomaldisorders.html </li></ul><ul><li>http://encarta.msn.com/media_461573602/geographic_distribution_of_the_sickle-cell_mutation.html </li></ul><ul><li>http://www.nhlbi.nih.gov/health/dci/Diseases/Sca/SCA_WhatIs.html </li></ul><ul><li>http://www3.nbnet.nb.ca/normap/cfsymptoms.htm </li></ul><ul><li>http://www.cff.org/home/ </li></ul>
  29. 29. More references… <ul><li>http://www.ninds.nih.gov/disorders/taysachs/taysachs.htm </li></ul><ul><li>http://www.pkunews.org/ </li></ul><ul><li>http://www.hemophilia.org/bdi/bdi_types1.htm </li></ul><ul><li>http://www.hdsa.org </li></ul><ul><li>http://www.nwabr.org/studentbiotech/winners/studentwork/2007/WB_BA_TRONGTHAM/7_diagnosis.htm </li></ul><ul><li>http://www.americanpregnancy.org/prenataltesting/ </li></ul>

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