医学遗传学 19遗传疾病的治疗eng v-精选文档.ppt
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1、Medical Genetics 1. What is gene therapy? Genes, which are carried on chromosomes, are the basic physical and functional units of heredity. Genes are specific sequences of bases that encode instructions on how to make proteins. Medical Genetics Although genes get a lot of attention, its the proteins
2、 that perform most life functions and even make up the majority of cellular structures. Medical Genetics When genes are altered so that the encoded proteins are unable to carry out their normal functions, genetic disorders can result. Medical Genetics Gene therapy is a technique for correcting defec
3、tive genes responsible for disease development. Medical Genetics Researchers may use one of several approaches for correcting faulty genes: 1. A normal gene may be inserted into a nonspecific location within the genome to replace a nonfunctional gene. This approach is most common. 2. An abnormal gen
4、e could be swapped for a normal gene through homologous recombination. 3. The abnormal gene could be repaired through selective reverse mutation, which returns the gene to its normal function. 4. The regulation (the degree to which a gene is turned on or off) of a particular gene could be altered. M
5、edical Genetics 2. How does gene therapy work? In most gene therapy studies, a “normal“ gene is inserted into the genome to replace an “abnormal,“ disease-causing gene. Medical Genetics A carrier molecule called a vector must be used to deliver the therapeutic gene to the patients target cells. Curr
6、ently, the most common vector is a virus that has been genetically altered to carry normal human DNA. Medical Genetics Viruses have evolved a way of encapsulating and delivering their genes to human cells in a pathogenic manner. Medical Genetics Scientists have tried to take advantage of this capabi
7、lity and manipulate the virus genome to remove disease-causing genes and insert therapeutic genes. Medical Genetics Target cells such as the patients liver or lung cells are infected with the viral vector. The vector then unloads its genetic material containing the therapeutic human gene into the ta
8、rget cell. Medical Genetics The generation of a functional protein product from the therapeutic gene restores the target cell to a normal state. Medical Genetics To reverse disease caused by genetic damage, researchers isolate normal DNA and package it into a vector, a molecular delivery truck usual
9、ly made from a disabled virus. Doctors then infect a target cell usually from a tissue affected by the illness, such as liver or lung cellswith the vector. The vector unloads its DNA cargo, which then begins producing the missing protein and restores the cell to normal. Medical Genetics A. Some of t
10、he different types of viruses used as gene therapy vectors (1) Retroviruses A class of viruses that can create double-stranded DNA copies of their RNA genomes. These copies of its genome can be integrated into the chromosomes of host cells. Human immunodeficiency virus (HIV) is a retrovirus. Medical
11、 Genetics (2)Adenoviruses A class of viruses with double-stranded DNA genomes that cause respiratory, intestinal, and eye infections in humans. The virus that causes the common cold is an adenovirus. (3)Adeno-associated viruses A class of small, single-stranded DNA viruses that can insert their gene
12、tic material at a specific site on chromosome 19. (4)Herpes simplex viruses A class of double-stranded DNA viruses that infect a particular cell type, neurons. Herpes simplex virus type 1 is a common human pathogen that causes cold sores. Medical Genetics Medical Genetics Medical Genetics Medical Ge
13、netics Besides virus-mediated gene- delivery systems, there are several nonviral options for gene delivery. The simplest method is the direct introduction of therapeutic DNA into target cells. This approach is limited in its application because it can be used only with certain tissues and requires l
14、arge amounts of DNA. Medical Genetics Another nonviral approach involves the creation of an artificial lipid sphere with an aqueous core. This liposome, which carries the therapeutic DNA, is capable of passing the DNA through the target cells membrane. Medical Genetics Therapeutic DNA also can get i
15、nside target cells by chemically linking the DNA to a molecule that will bind to special cell receptors. Medical Genetics Once bound to these receptors, the therapeutic DNA constructs are engulfed by the cell membrane and passed into the interior of the target cell. This delivery system tends to be
16、less effective than other options. Medical Genetics Researchers also are experimenting with introducing a 47th artificial human chromosome into target cells. This chromosome would exist autonomously alongside the standard 46 -not affecting their workings or causing any mutations. Medical Genetics It
17、 would be a large vector capable of carrying substantial amounts of genetic code, and scientists anticipate that, because of its construction and autonomy, the bodys immune systems would not attack it. A problem with this potential method is the difficulty in delivering such a large molecule to the
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