2018年医学遗传学 16肿瘤遗传学eng v-文档资料.ppt
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1、Medical Genetics The ancient Greeks believed that cancer was caused by too much body fluid they called “black bile.“ Medical Genetics Doctors in the seventeenth and eighteenth centuries suggested that parasites caused cancer. Today, doctors understand more about the link between cancer and genetics.
2、 Medical Genetics Viruses, ultraviolet (UV) radiation, and chemicals can all damage genes in the human body. If particular genes are affected, a person can develop cancer. Understanding how genes cause cancer, though, first requires a basic understanding of several genetic terms and concepts. Medica
3、l Genetics 1. General Cancer is a very common disease, affecting about 1 in 3 individuals, and about half the people that contract cancer will die as a direct result of their disease. Medical Genetics For the most part, cancer arises from a single cell, that is, cancer is a clonal disease. The avera
4、ge human being contains about 1014 cells (i.e., 100,000,000,000,000 cells), any one of which could, in principle, become a cancer cell, if it acquired the right sort of mutations while it still had the potential to proliferate. Medical Genetics Therefore, the cancer cell arises and progresses once o
5、ut of a possible 1014 cellular targets. That only happens in 1 in 3 people. Even then it usually takes 60 or 70 years to occur. Medical Genetics Medical Genetics Tumors are hereditary Hereditary retinoblastoma is an autosomal dominant trait in which susceptibility to retinoblastoma is inherited. Thi
6、s is an unusual “dominant“ trait in that a mutation in one RB gene is not sufficient to cause symptoms, but mutations in the second allele often arise during development. Medical Genetics Medical Genetics Offspring have a 50% chance of receiving the mutant gene from a heterozygous parent, and 90% of
7、 carriers will develop retinoblastoma, usually in both eyes. The hereditary form is also associated with a high risk for other cancers especially of the bone and fibrous tissues (osteosarcomas and fibrosarcoma. Medical Genetics Sporadic retinoblastoma is a trait in which the affected individual has
8、not inherited any mutant alleles of the retinoblastoma gene. Medical Genetics The mutations occur after birth and result in tumor formation. Tumors usually develop in only one eye and patients are not at high risk for other cancers. Both alleles need to be mutated in a single cell, and that is why t
9、his form typically occurs only in one eye. Medical Genetics Medical Genetics Chromosome and tumors Detailed studies of the Philadelphia chromosome show that most of chromosome 22 has been translocated onto the long arm of chromosome 9. In addition, the small distal portion of the short arm of chromo
10、some 9 is translocated to chromosome 22. This translocation, which is found only in tumor cells, indicates that a patient has chronic myelogenous leukemia (CML). In CML, the cells that produce blood cells for the body (the hematopoietic cells) grow uncontrollably, leading to cancer. Medical Genetics
11、 Medical Genetics Medical Genetics The connection between this chromosomal abnormality and CML was clarified by studying the genes located on the chromosomes at the sites of the translocation breakpoints. Medical Genetics In one of the translocated chromosomes, part of a gene called abl is moved fro
12、m its normal location on chromosome 9 to a new location on chromosome 22. This breakage and reattachment leads to an altered abl gene. The protein produced from the mutant abl gene functions improperly, leading to CML. Medical Genetics 2. oncogene Oncogenes are mutated forms of genes that cause norm
13、al cells to grow out of control and become cancer cells. They are mutations of certain normal genes of the cell called proto-oncogenes. Medical Genetics Proto-oncogenes are the genes that normally control how often a cell divides and the degree to which it differentiates (or specializes). When a pro
14、to-oncogene mutates (changes) into an oncogene, it becomes permanently “turned on“ or activated when it is not supposed to be. When this occurs, the cell divides too quickly, which can lead to cancer. Medical Genetics It may be helpful to think of a cell as a car. For it to work properly, there need
15、 to be ways to control how fast it goes. A proto-oncogene normally functions in a way that is similar to a gas pedal - it helps the cell grow and divide. An oncogene could be compared to a gas pedal that is stuck down, which causes the cell to divide out of control. Medical Genetics The pathway for
16、normal cell growth starts with growth factor, which locks onto a growth factor receptor. The signal from the receptor is sent through a signal transducer. A transcription factor is produced, which causes the cell to begin dividing. If any abnormality is detected, the cell is made to commit suicide b
17、y a programmed cell death regulator. Medical Genetics More than 100 oncogenes are now recognized, and undoubtedly more will be discovered in the future. Scientists have divided oncogenes into the 5 different classes. Medical Genetics Growth factors These oncogenes produce factors that stimulate cell
18、s to grow. The best known of these is called sis. It leads to the overproduction of a protein called platelet-derived growth factor, which stimulates cells to grow. Medical Genetics Growth factor receptors These are normally turned “on“ or “off“ by growth factors. When they are “on,“ they stimulate
19、the cell to grow. Certain mutations in the genes that produce these cause them to always be “on.“ In other cases, the genes are amplified. Medical Genetics This means that instead of the usual 2 copies of the gene, there may be several extras, resulting in too many growth factor receptor molecules.
20、As a result, the cells become overly sensitive to growth- promoting signals. Medical Genetics The best known examples of growth factor receptor gene amplification are erb B and erb B-2. These are sometimes known as epidermal growth factor receptor and HER2/neu. HER2/neu gene amplification is an impo
21、rtant abnormality seen in about one third of breast cancers. Both of these oncogenes are targets of newly developed anti-cancer treatments. Medical Genetics Signal transducers These are the intermediate pathways between the growth factor receptor and the cell nucleus where the signal is received. Li
22、ke growth factor receptors, these can be turned on or off. When they are abnormal in cancer cells, they are turned on. Medical Genetics Transcription factors These are the final molecules in the chain that tell the cell to divide. These molecules act on the DNA and control which genes are active in
23、producing RNA and protein. Medical Genetics The best known of these is called myc. In lung cancer, leukemia, lymphoma, and a number of other cancer types, myc is often overly activated and stimulates cell division. Medical Genetics Two well known signal transducers are abl and ras. Abl is activated
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