Lecture 11 Heredity and Cancer How do you know if you are at risk A family history that might indicate an inherited gene mutation would include 2 or more of the following Cancer in several closely related people on same side of family in several generations Cancer at younger ages than usual More than one diagnosis of cancer in same person Specific types of cancer that are linked to specific genes Occur in any of the cells of the body somatic except the germ cells sperm and egg How are mutations inherited Somatic mutations occur after conception thus not passed on to children Can cause cancer other diseases Inherited mutations occur before conception Do occur in germ cells thus ARE passed on to children Can cause cancer or other diseases Facts about inherited cancer Only 5 10 of all cancers are related to an inherited gene mutation Inheriting the gene mutation does NOT mean that the child is born with cancer The child inherits a higher risk of developing cancer sometime during his her life Genetic terminology position Homologous chromosomes contain genes for the same biological features in same Alleles paired forms a gene one on each homologue Penetrance frequency with which an allele yields an expected train in a population hereditary risk examples Genes affecting DNA repair xeroderma pigmentosum Genes involved in tumor suppression retinoblastoma Xeroderma pigmentosum requires 2 copies of mutant gene to be inherited one from each parent Results in absence of DNA repair Carriers exhibit no disease symptoms but can pass gene on to children Each child have 50 chance of inheriting mutant gene from each parent Xeroderma Pigmentosum Patients are sensitive to UV sunlight could be fatal Minimal sunlight exposure leads to skin cancer Benefits of genetic testing Allow more accurate assessment of cancer risk If positive doctors can screen earlier for cancers If negative individuals may not have to screen as aggressively Early cancer screening can be offered to other at risk family members if mutations is identified No physical risks Risks of genetic testing Can be emotionally difficult regardless of results Emotional stress on relatives who have not had genetic testing Health insurance coverage for cancer screening Possibility of employer insurance provider discrimination based on genetic test results Effect of birth year on breast cancer risk Women born after 1940 carrying mutations in BRCA 1 or 2 genes have higher breast cancer rates than women born before 1940 who carry the same mutations This difference indicates that non genetic factors influence breast cancer risks even in individuals who inherit high risk mutations
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