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GeneticDisorders-I

lecture 24 wilson

QuestionAnswer
# 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 on 2011-10-02



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