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Genetic and Congenital Disorders Unit One Chapter Four Single Gene Disorders Allele Homozygous Heterozygous Genotype Phenotype Autosomal Dominant Disorders Males and females equally affected If parents don’t have the trait, the children won’t 50% transmission No skipping of generations – Penetrance – Expressivity Autosomal Dominant Disorders Marfan’s syndrome – Connective tissue disorder – Manifested in the eyes, skeleton and Cardiovascular system Retinal detachment Long thin body Aortic dissection Autosomal Dominat Disorders Familial Hypercholesterolemia – Premature coronary artery disease (CAD) – Strong family history of CAD Multiple Myocardial Infarctions in 3rd and 4th decade Adults with cholesterol levels >300mg/dl Children’s levels > 250mg/dl Autosomal Recessive Disorders Only manifested when both alless are affected If heterozygous then parent may be a carrier of the mutation Usually seen early in life Males and females equally affected 25% transmission Consanguinity Autosomal Recessive Disorders Pheylketonuria (PKU) – Enzyme defect Increased levels of phenylalanine in blood Profound mental retardation Special diet Autosomal Recessive Disorders Cystic Fibrosis Multisystem involvement – Respiratory – Pancreatic – Gastrointestinal X-linked disorders Disorders almost always linked to X chromosome Predominantly Recessive Mother to son mutation Mother to daughter carrier 50% transmission X- linked disorders Fragile X syndrome – Mental retardation – Typical phenotypic appearance Long face and mandible Large ears Macroorchidism X-linked disorders Hemophilia A ( factor VIII deficiency) Lifelong tendency to hemorrhage – Deep soft tissue bleeding and hemathrosis Multifactorial Disorders Factors include genetic and environmental Threshold phenomenon Cleft Lip, congenital hip dislocation, pyloric stenosis. Review You are educating a parent of a child with Familial hypercholesterolemia . How would you address.. – Probability of transmission – Carrier status – Skipped generations Review Autosomal recessive disorders are heterozygous/ homozygous? X-linked disorders are passed mother to son / daughter How common is fragile X syndrome? Chromosomal Disorders Mosaicism: Alteration in duplication Aneuploidy: Alteration in numbers – Monosomy: Turners’s syndrome (45XO) – Polysomy: Trisomy ( 13,18,21) – Klinefelter’s ( XXY) Trisomy 21 – Downs Syndrome Most common cause of mental retardation – IQ range 25-60 Typical phenotypic features Period of Vulnerability Orgnagenesis days 15-60 post conception Early environmental influences Each organ has a critical timeframe Teratogenic agents An environmental agent that induces structural malformation, growth deficiency, and/or functional alterations – Radiation – Chemicals/Drugs – Infectious agents Clinical Tetralogy Prevention of malformation – Fetal alcohol syndrome – Folic acid – Vaccinations Review Turners syndrome is a monosomy/ polysomy condition. Folic acid can help prevent what type of defects? The surgeon general has suggested a save number of alcoholic drinks per day for a pregnant women. What is this number?
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