{"id":384,"date":"2019-06-24T13:10:20","date_gmt":"2019-06-24T17:10:20","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/053humanbiology\/chapter\/5-17-case-study-conclusion-cancer-in-the-family\/"},"modified":"2022-01-19T15:39:45","modified_gmt":"2022-01-19T20:39:45","slug":"5-17-case-study-conclusion-cancer-in-the-family","status":"publish","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/053humanbiology\/chapter\/5-17-case-study-conclusion-cancer-in-the-family\/","title":{"raw":"5.18\u00a0Case Study Conclusion: Cancer in the Family","rendered":"5.18\u00a0Case Study Conclusion: Cancer in the Family"},"content":{"raw":"Created by: CK-12\/Adapted by Christine Miller\n\n[caption id=\"attachment_383\" align=\"aligncenter\" width=\"500\"]\"Pedigree Figure 5.18.1 Pedigree for Rebecca's family, as described in the beginning of this chapter, showing individuals with cancer (red) and those that do not have cancer (blue). Circles represent women, squares represent men.<\/em>[\/caption]\n\n
\n\nCase Study Conclusion: Cancer in the Family<\/strong>\n\n<\/div>\nRebecca\u2019s family tree, as illustrated in the [pb_glossary id=\"1580\"]pedigree[\/pb_glossary] above (Figure 5.18.1), shows a high incidence of [pb_glossary id=\"1268\"]cancer[\/pb_glossary] among close relatives. But are [pb_glossary id=\"1226\"]genes[\/pb_glossary] the cause of cancer in this family? Only genetic testing, which is the sequencing of specific genes in an individual, can reveal whether a cancer-causing gene is being inherited in this family.\n\nFortunately for Rebecca, the results of her genetic testing show that she does not have the [pb_glossary id=\"2105\"]mutations[\/pb_glossary] in the BRCA1 and BRCA2 genes that most commonly increase a person\u2019s risk of getting cancer.\u00a0This doesn't mean, however,\u00a0that she doesn\u2019t have\u00a0other<\/em> mutations in these genes that could increase her risk of getting cancer. There are many other mutations in BRCA genes whose effect on cancer risk is still not known \u2014 and there may be many more yet to be discovered. Figure 5.18.2 from the National Cancer Institute illustrates many of the different types of known mutations in the BRCA1 gene. It is important to continue to study the variations in genes such as BRCA in different people to better assess their possible contribution to the development of disease. As you now know from this chapter, many mutations are harmless, while others can cause significant health effects, depending on the specific mutation and the gene involved.\n\n[caption id=\"attachment_383\" align=\"aligncenter\" width=\"570\"]\"Mutations Figure 5.18.2 Use the knowledge you gained from this chapter to define nonsense, frameshift, and missense mutations. Do these tend to be neutral or harmful mutations?<\/em>[\/caption]\n\nMutations in BRCA genes are particularly likely to cause cancer because these genes encode for tumor-suppressor proteins that normally repair damaged DNA and control cell division. If these genes are mutated in a way that causes the proteins to not function properly, other mutations can accumulate and cell division can run out of control, which can cause cancer.\n\nBRCA1 and BRCA2 are on chromosomes 17 and 13, respectively, which are autosomes. As Rebecca\u2019s genetic counselor mentioned, mutations in these genes have a dominant inheritance pattern. Now that you know the pattern of inheritance of [pb_glossary id=\"1799\"]autosomal[\/pb_glossary] dominant genes, if Rebecca\u2019s grandmother\u00a0did<\/em> have one copy of a mutated BRCA gene, what are the chances that Rebecca\u2019s mother also has this mutation? Because it is dominant, only one copy of the gene is needed to increase the risk of cancer, and because it is on autosomes instead of sex chromosomes, the sex of the parent or offspring does not matter in the inheritance pattern. In this situation, Rebecca\u2019s grandmother\u2019s eggs would have had a 50 per cent chance of having a BRCA gene mutation (Mendel\u2019s law of segregation). Therefore, Rebecca\u2019s mother would have had a 50 per cent chance of inheriting this gene. Even though Rebecca does not have the most common BRCA mutations that increase the risk of cancer, it does not mean that her mother does not, because there would also only be a 50 per cent chance that she would pass it on to Rebecca. Rebecca\u2019s mother, therefore, should consider getting tested for mutations in the BRCA genes, as well. Ideally, the individuals with cancer in a family should be tested first when a genetic cause is suspected, so that if there is a specific mutation being inherited, it can be identified, and the other family members can be tested for that same mutation.\n\nMutations in both BRCA1 and BRCA2 are often found in Ashkenazi Jewish families. However, these genes are not linked in the chromosomal sense, because they are on different chromosomes and are therefore inherited independently, in accordance with Mendel\u2019s law of independent assortment. Why would certain gene mutations be prevalent in particular ethnic groups? If people within an ethnic group tend to produce offspring with each other, their genes will remain prevalent within the group. These may be genes for harmless variations such as skin, hair, or eye colour, or harmful variations such as the mutations in the BRCA genes. Other genetically based diseases and disorders are sometimes more commonly found in particular ethnic groups, such as cystic fibrosis in people of European descent, and sickle cell anemia in people of African descent. You will learn more about the prevalence of certain genes and traits in particular ethnic groups and populations in the chapter on Human Variation.<\/em>\n\nAs you learned in this chapter, genetics is not the sole determinant of phenotype. The environment can also influence many traits, including adult height and skin colour. The environment plays a major role in the development of cancer, too. Ninety to 95 per cent of all cancers do not have an identified genetic cause, and are often caused by mutagens in the environment, such as UV radiation from the sun or toxic chemicals in cigarette smoke. But for families like Rebecca\u2019s, knowing their family health history and genetic makeup may help them better prevent or treat diseases that are caused by their genetic inheritance. If a person knows they have a gene that can increase their risk of cancer, they can make lifestyle changes and have early and more frequent cancer screenings. They may even choose to have preventative surgeries that can help reduce their risk of getting cancer and increase their odds of long-term survival if cancer does occur. The next time you go to the doctor and they ask whether any members of your family have had cancer, you will have a deeper understanding why this information is so important to your health.\n
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Chapter 5 Summary<\/span><\/h1>\n<\/header>\n
\n\nIn this chapter you learned about genetics \u2014 the science of heredity. Specifically you learned that:\n