Unit 6 Human Disease

1. Unit 6Human Disease (additional reference – Chapter 7 of Textbook) Congenital and Genetic Disorders Pathophysiology - Borders

2. Overview • A genetic disorder is a disease caused by a variation in an individual’s DNA, or an alteration of a gene called a mutation. • Many diseases have a genetic aspect. For example, many cancers are caused by a mutation in a gene or group of genes in a person's cells. These mutations can occur randomly or because of an environmental exposure such as cigarette smoke. • Other genetic disorders are inherited. A mutated gene is passed down through a family and each generation of children can inherit the gene that causes the disease. • Still other genetic disorders are due to problems with the number of packages of genes called chromosomes. There can be extra copies of genes, missing genes, or translocated genes (Website link) Genetic Disorder's Interactive

3. Genetics • Genetic material, or genes, in a cell’s nucleus, contain information for all of an individual’s traits. • The genes are comprised of sequenced nucleic acids which determine all of the functions of an individual’s body cells. • There are 22 pairs of chromosomes called autosomes and a 23rd pair of sex chromosomes making a total of 46 chromosomes. • A karyotype charts these chromosomes.

4. Karyotyping A karyotype is an individual's collection of chromosomes. The term also refers to a laboratory technique that produces an image of an individual's chromosomes. The karyotype is used to look for abnormal numbers or structures of chromosomes.

5. Gene Mapping Gene mapping is the process of establishing the locations of genes on the chromosomes. Researchers using gene maps to help cure diseases. Genetic mapping is on the cutting edge of disease prevention.

6. Genetic Testing • Genetic Counseling • Pedigree Analysis • Blood test for proteins • Phenotype analysis • Fetal Testing • Karyotype • Amniocentesis • Chorionic villus sampling (CVS) • Newborn Testing

7. Chorionic Villus Sampling Chorionic villus sampling (CVS) is the removal of a small piece of placenta tissue (chorionic villi) from the uterus during early pregnancy to screen the baby for genetic defects.

8. Genetic Abnormalities Examples of Chromosomal Mutations – • Deletion –missing a gene • Duplication – sequence repeated • Translocation –chromosome attached to another one

9. Chromosomal Errors: Problems in Meiosis • Nondisjunction- Failure of paired chromosomes to disjoin (separate) during cell division so that both chromosomes go to one daughter cell and none to the other • Aneuploidy- One or a few chromosomes above or below the normal chromosome number. For example, three number 21 chromosomes or trisomy 21 is a form of aneuploidy. • Monosomy • Trisomy • Polyploidy

10. Genetic Counseling • Pedigree can help us understand the past & predict the future • Thousands of genetic disorders are inherited as simple recessive traits • from benign conditions to deadly diseases • albinism • cystic fibrosis • Tay-sachs • sickle cell anemia • PKU

11. Chromosomal Sex-linked Disorders • Fragile X Syndrome Occurs in about 1 of 1,200 males and 1 of 2,500 females. Results from a breakage of the tip of an X chromosome. • Klinefelter Syndrome(XXY, XXXY, XXXXY) Occurs in about 1 of 1,000 males. It is caused by an extra X chromosome

12. Turner Syndrome • Nondisjunction of the X • Occurs in about 1 of 10,000 females. • This condition occurs in about 1 in 2,500 • More common among pregnancies that do not survive to term (miscarriages and stillbirths). • These women have immature female appearance, do not develop secondary sex characteristics, and lack internal reproductive organs.

13. Chromosomal Sex-linked Disorders • Superfemale Syndrome (XXX, XXXX, XXXXX) Occurs in about 1 of 1,000 females. Women appear normal, but tend to score slightly below average in intelligence. • Supermale Syndrome (XYY, XYYY, XYYYY) Occurs in about 1 0f 1,000 males. The men tend to be taller than average, with a greater incidence of acne and minor skeletal abnormalities.

14. Phenylketonuria PKU • Recessive autosomal disease • Inability to produce enzyme to break down specific amino acid • Build up of amino acid leads to mental retardation if it is not avoided. • PKU testing of babies

15. CysticFibrosis • Recessive autosomal gene • Effects 1 in 2,500 Whites • Caused by defective transport protein • Results in organs clogged with mucus, premature death.

16. delta F508 loss of oneamino acid

17. Effecton Lungs Chloride channel transports salt through protein channel out of cell Osmosis: H2O follows Cl– normal lungs airway Cl– Cl– channel H2O cells lining lungs cystic fibrosis Cl– H2O bacteria & mucus build up thickened mucus hard to secrete mucus secreting glands

18. Tay-Sachs Disease • Recessive autosomal disease • Caused by defective enzyme; therefore fats build up and ruin the brain • Results in nervous system deterioration and early death

19. Tay-Sachs Disease • Primarily Jews of eastern European (Ashkenazi) descent & Cajuns (Louisiana) • strikes 1 in 3600 births • 100 times greater than incidence among non-Jews • non-functional enzyme fails to breakdown lipids in brain cells • fats collect in cells destroying their function • symptoms begin few months after birth • seizures, blindness & degeneration of muscle & mental performance • child usually dies before 5years old

20. Sickle Cell Anemia • Recessive autosomal disease • Effects 1 in 500 African- • Americans • Causes anemia, poor blood circulation

21. Sickle Cell Anemia • Primarily Africans • strikes 1 out of 400 African Americans • high frequency • caused by substitution of a single amino acid in hemoglobin • when oxygen levels are low, sickle-cell hemoglobin crystallizes into long rods • deforms red blood cells into sickle shape • sickling creates pleiotropiceffects = cascade of other symptoms

22. Sickle Cell Anemia Substitution of one amino acid in polypeptide chain hydrophilicamino acid hydrophobic amino acid

24. 1872 Huntington’s Chorea • Dominant inheritance • repeated mutation on end of chromosome 4 • mutation = CAG repeats • glutamine amino acid repeats in protein • one of 1st genes to be identified • build up of “huntingtin” protein in brain causing cell death • memory loss • muscle tremors, jerky movements called “chorea” • starts at age 30-50 • early death • 10-20 years after start

25. Huntington’s Disease

26. Down Syndrome In most cases, Down syndrome occurs when there is an extra copy of chromosome 21, or Trisomy 21. The extra chromosome causes problems with body and brain development. • Brushfield Spots • Simian Crease • Large gap between toes

27. Progeria • Mutation in egg or sperm • Mutation of protein lamin A which holds nucleus together. • Uncommon: 1 in 10 million births • Results in aging rates 10 times that of normal, death usually before 18.

28. Genetics & Culture • Why do all cultures have a taboo against incest? • laws or cultural taboos forbidding marriages between close relatives are fairly universal • Fairly unlikely that 2 unrelated carriers of same rare harmful recessive allele will meet & mate • but matings between close relatives increase risk • “consanguineous” (same blood) matings • individuals who share a recent common ancestor are more likely to carry same recessive alleles