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DNA repair
DNA repair
Some relatively rare autosomal recessive diseases associated with abnormalities of DNA repair predispose to the development of cancer.
Patients with xeroderma pigmentosum have a defect in their ability to repair DNA damage caused by ultraviolet light and by some chemicals, leading to a high incidence of skin cancer. The ataxia telangiectasia mutation results in an increased sensitivity to ionizing radiation and an increased incidence of lymphoid tumours. An increased susceptibility to lymphoid malignancy is also seen in Bloom's syndrome and Fanconi's anaemia. It is not known why these chromosome-break syndromes predispose to tumours of lymphatic tissue.
The following are examples of cancer syndromes that exhibit dominant inheritance:
- Retinoblastoma , an eye tumour found in young children. It occurs in both hereditary (40%) and non-hereditary (60%) forms. The 40% of patients with the hereditary form have a germline mutation on the long arm of chromosome 13 that predisposes to retinoblastoma. In addition to the latter, children inheriting this mutation at the so-called RB1 locus are at risk for developing other tumours, particularly osteosarcoma.
- Breast and ovarian cancer. Two genes have been identified - BRCA1 and BRCA2 . A strong family history along with germline mutation of these genes accounts for most cases of familial breast cancer and over half of ovarian cancers. BRCA1 and 2 proteins bind to the DNA repair enzyme Rad51 to make it functional in repairing DNA breaks. Mutations in the BRCA genes will lead to accumulation of unrepaired mutations in tumour-suppressor genes and crucial oncogenes.
- Neurofibromatosis . Inactivation of the NF1 gene will lead to constitutive activation of ras proteins.
- Multiple-endocrine-adenomatosis syndromes. Multiple endocrine neoplasia type 2 (MEN2) is now thought to be associated with mutations in the RET proto-oncogene on chromosome 10 and as such is the exception to all the other syndromes which involve tumour suppressor genes.
Cancer Tip |
Fruit and vegetable consumption may not significantly reduce breast cancer risk, but fruits and vegetables contain phytochemicals and antioxidants that may be protective against other cancers and heart disease. A minimum of five servings per day is recommended.
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Health Tip |
Discovering new ways of communicating with someone after a stroke may do more than anything else to help the person.
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