lecture 24 wilson
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| # of base pairs in human genome | ~ 3 billion bps
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| percent of spontaneous abortuses in early gestations that were due to genetic abnormalities | up to 50%
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| # of genes in human genome | 30,000 genes
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| what percent of human genome encodes proteins? | < 2%
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| functional cloning | one starts with the clinical phenotype and the enzyme that's affected and works backwards to clone the gene
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| positional cloning | closer to the standard idea of cytogenetics, identification of possible genes by mapping to specific chr loci
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| examples of diseases that are treated with recombinant DNA technology | erythropoietin for anemia, tPA for thrombotic episodes, myeloid factors for stimulating BM growth, TNF receptor for RA
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| examples of dz that is treated with gene therapy | transplantation of a somatic cell that's been transfected with a normal gene, used in deaminase deficiency. downfall: hard to get the genes expressed in the right tissues
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| definition of mutation | permanent change in DNA
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| 3 categories of mutations | 1) single gene mutations with large effects (sickle cell anemia) // 2) chr disorders (Down syndrome) // 3) complex multigenic disorders (HTN, multifactorial inheritance)
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| mechanisms of gene mutations | missense (sickle cell anemia), nonsense (beta-thalassemia) and frameshift (normal generation of O blood group phenotype)
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| 4 major categories of genetic dz | disorders of mutant genes with large effect (Mendelian), multifactorial inheritance, chr disorders, non-classic/non-Mendelian inheritance
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| autosomal dominant inheritance pattern | heterozygotes express phenotype of STRUCTURAL PROTEIN ABNORMALITY, @ least one parent is always affected, males and females affected equally and all can transmit
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| autosomal recessive inheritance pattern | homozygotes express the phenotype of ENZYME DEFICIENCY (classically), trait doesn't effect parents who are carriers, 25% recurrence risk, associated with higher incidence of consanguinity
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| X-linked recessive inheritance pattern | typical granfather --> grandson transmission, father makes all his daughter carriers, sons of heterozygous women have 50% risk of having dz
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| X-linked dominant inheritance pattern | very rare, affected father transmits to all of his daughters but NONE of his sons, affected heterozygous mothers transmit with 50% chance to all children
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| 4 categories of single gene or Mendelian disorders | 1) defects in structural proteins // 2) defects in receptor, transmembrane proteins // 3) defects in enzymes // 4) defects in proteins regulating cell growth
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| Marfan syndrome | defects in structural protein fibrillin, which serves as scaffolding for deposition of elastin. phenotype: subluxation of lens, tall stature with long ext/arachnodactyly, scoliosis, dilated aortic root, aortic dissections (up to whole body vol in wall)
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| cystic medionecrosis of aorta | clinical feature of Marfan's syndrome, predisposition to hemorrhage within the walls of the aorta causing fusiform aneurysm
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| inheritance pattern of Marfan syndrome | autosomal dominant with 20% of cases being due to new mutations
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| Ehlers-Danlos syndrome | mostly AD dz typified by defects in structural protein collagen. phenotype: hyperextensible joints and skin, cigarette paper scars (from shallow scarring after defective repair), aortic rupture
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| CF | AR dz characterized by defective CFTR (transmembrane protein) that doesn't regulate Na/H20 well causing mucus to be dehydrated and thick in the lungs, biliary tree & pancreas. traps bacteria in lungs = pneumonia. increased NaCl in sweat
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| positive sweat chloride test | used to diagnose CF and determine clinical phenotype. if (+) then pt likely to have bronchiectasis, hepatic cirrhosis, pancreatic insufficiency and male infertility
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| negative sweat chloride test | pt can still have CF but the more mild phenotype. azoospermia, sinusitis, absence of vas deferens (all as sole abnormalities)
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| genetic and environmental modifiers of CF severity | CF modifer locus or CFM-1 = severity of meconium ileus, MBL-immunity for opsonization, virulence of infecting organism(s), exposure to smoking or other allergens
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| classification of mutations in CF | can be due to defective protein synthesis, abnl protein folding, processing or trafficking, defective regulation, decreased conductance, reduced abundance, altered regulation of separate ions
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