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GeneticDisorders-I
lecture 24 wilson
| Question | Answer |
|---|---|
| # of base pairs in human genome | ~ 3 billion bps |
| percent of spontaneous abortuses in early gestations that were due to genetic abnormalities | up to 50% |
| # of genes in human genome | 30,000 genes |
| what percent of human genome encodes proteins? | < 2% |
| functional cloning | one starts with the clinical phenotype and the enzyme that's affected and works backwards to clone the gene |
| positional cloning | closer to the standard idea of cytogenetics, identification of possible genes by mapping to specific chr loci |
| 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 |
| 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 |
| definition of mutation | permanent change in DNA |
| 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) |
| mechanisms of gene mutations | missense (sickle cell anemia), nonsense (beta-thalassemia) and frameshift (normal generation of O blood group phenotype) |
| 4 major categories of genetic dz | disorders of mutant genes with large effect (Mendelian), multifactorial inheritance, chr disorders, non-classic/non-Mendelian inheritance |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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) |
| cystic medionecrosis of aorta | clinical feature of Marfan's syndrome, predisposition to hemorrhage within the walls of the aorta causing fusiform aneurysm |
| inheritance pattern of Marfan syndrome | autosomal dominant with 20% of cases being due to new mutations |
| 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 |
| 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 |
| 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 |
| negative sweat chloride test | pt can still have CF but the more mild phenotype. azoospermia, sinusitis, absence of vas deferens (all as sole abnormalities) |
| 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 |
| 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 |
Created by:
sirprakes
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