hereditaryandfuture

hereditaryandfuture - Hereditary cancers and genetic...

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Hereditary cancers and genetic screening Most cancer risk (80-90%) arise from non-hereditary risk factors o These risk factors include smoking and exposure to other carcinogens, exposure to sunlight, dietary choices and obesity. 10-20% cancers arise from hereditary or familial predisposition to develop cancer o Many of the genes that lead to this likelihood of developing cancer have been located Some of these include: Gene class/syndrome Mutant Genes Cancer Types Inheritance pattern Tumor Suppressor Retinoblastoma RB Retinal tumors Dominant Familial adenomatous polyposis (FAP) APC Colon Dominant Li-Fraumeni syndrome p53 Many including breast, brain, leukemia and sarcomas Dominant Tumor Suppressor/ DNA repair Familial breast cancer BRCA1,BRCA2 Breast, Ovary Dominant Hereditary nonpolyposis colon cancer (HNPCC) MSH2,MSH3,MSH4 and others Colon Dominant Xeroderma pigmentosum XPA,XPB.XPC AND others Skin Recessive Proto-oncogene (gain of function) Multiple endocrine neoplasia type II RET Thyroid Dominant Family history and pedigree analysis reveals predominance of cancer in families with these inherited genetic mutations. For example, the inherited loss of p53 leads to development of numerous cancers.
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Dominant vs recessive cancer risk syndromes This terminology can be confusing based upon what we normally call dominant and recessive. Most inherited cancers involve mutation of tumor suppressor genes (including DNA repair genes). These are therefore recessive mutations because both copies must be inactivated before cancer will develop. However, some of these mutations display a dominant cancer-risk because inherited one bad copy greatly (90%) increases the likelihood of mutation or loss of the second copy. Examples of dominant cancer risk syndromes include the inherited colon cancer syndromes (FAP and HNPCC) an BRCA1 and BRCA2 mutations. Other conditions, such as xeroderma pigmentosum are considered recessive cancer risk-syndromes because inheritance of 1 bad copy does not greatly predispose one to mutation or loss of the other copy. FAP vs HNPCC in Colon Cancer Most inherited or sporadic cases of colon cancer arise by a sequential accumulation of specific oncogenic and tumor suppressor genetic muations. FAP is characterized by inherited disruption of one allele of a tumor
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suppressor gene, APC. Patients prematurely develop 1000’s of benign colonic polyps. Subsequent mutations lead to malignancy. Additional mutations are acquired at a normal rate. HNPCC is characterized by inherited disruption of DNA mismatch repair genes Patients do not initially have numerous polyps. Initial tumor development is
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hereditaryandfuture - Hereditary cancers and genetic...

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