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Classes of Monogenic Disorders Autosomal Dominant and Recessive Inheritance Tuesday, October 26, 2010 Autosomal Dominant Inheritance 1 Examples of Monogenic Disorders Polycystic Kidney disease Sickle Cell anemia Cystic Fibrosis X-linked Hemophilia Tuesday, October 26, 2010 Galactosemia Autosomal Dominant Inheritance 3 Tuesday, October 26, 2010 • In dominant genetic diseases, the defective gene overcomes the normal gene and disease occurs • there is a whole spectrum of levels of dominance, depending on how much damage a bad gene does and how adequately the second normal gene can compensate for the failing defective gene. • a dominant disease affects a gene for a structural protein, causing malformed proteins that cause disease Autosomal Dominant Inheritance Autosomal Dominant Inheritance 4 Inheritance Pattern for Autosomal Dominant Disorders Dominance Tuesday, October 26, 2010 2 • These are diseases caused by an error in a single DNA gene. • Autosomal means the errors occurs on chromosome 1..22 rather than on the 23rd sex-linked X chromosome. • Some examples of autosomal dominant diseases are Huntington's disease , achondroplasia (dwarfism), Polycystic Kidney disease and Marfan Syndrome Marfan Syndrome Autosomal Recessive Autosomal Dominant Inheritance Autosomal Dominant Traits Hutington Disease Autosomal Dominant Tuesday, October 26, 2010 5 • • • • No carriers Usually inherited Parent-to-child transmission Both affected parents to child transmission • Double-dominant parent to child transmission • Undiseased parents to child transmission • Vertical inheritance October 26, 2010 6 Gender bias Autosomal Dominant Inheritance •Tuesday, 1 Double-dominance Sporadic Genetic Disease • usually causes very severe disease or even spontaneous abortion or stillbirth. • Double dominance is usually only possible for a child born to parents that both have the same dominant genetic disease, • A double-dominant disease is like a recessive disease, except that carriers of it have the ordinary single-dominant condition. • For example, the genetic dominant condition of achondroplasia(dwarfism) • A genetic disease that occurs when neither parent has any genetic defect. • These cases arise via random genetic mutations in the DNA. • A sporadic genetic mutation is more likely for a dominant disease than for a recessive genetic disease. Tuesday, October 26, 2010 Tuesday, October 26, 2010 Autosomal Dominant Inheritance 7 Autosomal Dominant Inheritance 8 Chromosome Genetic Diseases Causes of Chromosome Diseases • These are genetic diseases where a large part of the genetic code has been disrupted. • Chromosomes are long sequences of DNA that contain several genes. • Humans have 2 copies of each of the 23 chromosomes • arise from huge errors in the DNA that result from having extra chromosomes, large missing sequences, or other major errors. • caused by a random physical error during reproduction and are not inherited diseases Tuesday, October 26, 2010 Chromosome Diseases 9 Tuesday, October 26, 2010 Chromosome Diseases 10 Spontaneous Chromosome Errors Types of Chromosome Diseases • arise spontaneously from parents where neither has the disease. • elderly ladies are more likely to have babies with Down syndrome. • Many chromosome errors cause the fetus to be aborted before birth, but some syndromes can be born and survive • There are several common types of chromosome errors that cause disease. • The following major classes of chromosome diseases can occur: – Trisomy conditions e.g. Down syndrome – Monosomy conditions e.g. Turner syndrome). – Sex chromosome conditions Tuesday, October 26, 2010 Chromosome Diseases 11 Tuesday, October 26, 2010 Chromosome Diseases 12 2 Rarer Types of Chromosome Diseases Non-contagiousness of chromosome diseases • There are also some other rarer types of chromosome conditions that may lead to diseases – Translocation disorders e.g. Translocation Down • Genetic and chromosome diseases occur at birth. • Not infectious diseases • You are either born with the error in your chromosomes or not • Genetic tests by antenatal testing for genetic diseases Syndrome – Subtraction disorders – Mosaicisim – One-sided chromosome disorders Tuesday, October 26, 2010 Chromosome Diseases 13 1. Sex Chromosome Conditions Tuesday, October 26, 2010 Chromosome Diseases 14 2. Autosomal Trisomy Chromosome Diseases • Sex chromosome defects: • Turner syndrome (XO syndrome, monosomy X, missing Y): • Klinefelter syndrome (XXY syndrome, also rarely XXXY): • Jacobs syndrome (XYY syndrome): • Triple-X (XXX, also XXXX or XXXXX): • Down syndrome (trisomy 21): • Edwards syndrome (trisomy 18): • Patau syndrome (trisomy 13): Note that there is no ordering, and XYX would be the same as XXY. Tuesday, October 26, 2010 Chromosome Diseases 15 Miscarriages Caused by Trisomy Tuesday, October 26, 2010 Chromosome Diseases 16 Causes of Trisomy • trisomies at autosomes 13, 15, 18, and 21. • Trisomy at the other autosomes are probably fatal in embryos leading to spontaneous miscarriage. • frequency of natural miscarriages, around 1-in-5, • Down syndrome occurs more frequently in older women, one might theorize of the reason why. • Aging mothers. • ability to recognize wrong cells in a fetus is lost. • uterus is an immune-privileged site during pregnancy. Tuesday, October 26, 2010 Tuesday, October 26, 2010 Chromosome Diseases 17 Chromosome Diseases 18 3 3. Monosomy and Autosome Subtraction Disorders Polygenic Diseases • Cri-du-chat syndrome (cat's cry): • Prader-Willi Syndrome (PWS) and Angelman Syndrome (AS): • Uniparental Disomy Tuesday, October 26, 2010 Chromosome Diseases 19 • polygenic diseases are affected by many genes. • They have limited genetic basis. • a child inherited a genetic predisposition • E.g. cancers, heart disease, autoimmune diseases, etc. • family history is a risk factor for the disease Tuesday, October 26, 2010 Chromosome Diseases 20 4