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A cancer syndrome or family cancer syndrome is a genetic disorder in which inherited genetic mutations in one or more genes predisposes the affected individuals to the development of cancers and may also cause the early onset of these cancers. Although cancer syndromes exhibit an increased risk of cancer, the risk varies.
The central role of DNA damage and epigenetic defects in DNA repair genes in carcinogenesis. DNA damage is considered to be the primary cause of cancer. [17] More than 60,000 new naturally-occurring instances of DNA damage arise, on average, per human cell, per day, due to endogenous cellular processes (see article DNA damage (naturally occurring)).
The schematic diagram indicates the roles of insufficient DNA repair in aging and cancer, and the role of apoptosis in cancer prevention. An excess of naturally occurring DNA damage, due to inherited deficiencies in particular DNA repair enzymes, can cause premature aging or increased risk for cancer (see DNA repair-deficiency disorder).
Exposure to these chemicals causes several kinds of DNA damage: DNA adducts, oxidative stress, and breaks in the DNA strands. [67] Being around tobacco smoke – called passive smoking – can also cause lung cancer. Living with a tobacco smoker increases one's risk of developing lung cancer by 24%.
A metabolite of benzopyrene forms an intercalated DNA adduct, at center. In molecular genetics, a DNA adduct is a segment of DNA bound to a cancer-causing chemical. This process could lead to the development of cancerous cells, or carcinogenesis. DNA adducts in scientific experiments are used as biomarkers of exposure.
As examples, DNA damaging effects have been reported for acrolein, [14] formaldehyde, [15] and acrylonitrile. [16] Breast cancer is the second most frequent cancer worldwide on a yearly basis [(1.38 million cases, 10.9% of all cancer cases), and ranks 5th as cause of death (458,000, 6.1% of all cancer deaths)]. [12]
Hydrogen abstraction causes radical formation at the reacted carbon. The carbon radical reacts with molecular oxygen, which leads to a strand break in the DNA through a variety of mechanisms. [11] 1,4-Didehydrobenzene is able to position itself in such a way that it can abstract proximal hydrogens from both strands of DNA. [12]
Although silencing of some genes in cancers occurs by mutation, a large proportion of carcinogenic gene silencing is a result of altered DNA methylation (see DNA methylation in cancer). DNA methylation causing silencing in cancer typically occurs at multiple CpG sites in the CpG islands that are present in the promoters of protein coding genes.