Hereditary predispositions are present for a range of cancers. In some cases there may be a multifactorial link, as evidenced by the higher rate of lung cancer relative to controls in the non-smoking relatives of patients with this condition. There is no certainty that the relatives will develop lung cancer, but they are at higher relative risk.
However, for some forms of cancer there is a far greater chance of developing the condition associated with the carriage of a given gene defect within a family: SYNDROME CHROMOSOME GENE DEFECT
Certain cancers provide a model for understanding the molecular mechanisms of hereditary susceptibility. A prime example is retinoblastoma where two forms of the Rb gene exists on chromosome locus 13q. In the hereditary form, each cell has a normal and abnormal copy of the gene. The normal gene dictates that the cell remains normal until this copy is itself mutated, a not infrequent event. Consequently, bilateral retinoblastomas develop at an early age as soon as somatic mutation has occurred in one gene in one cell in both eyes. A sporadic form of retinoblastoma occurs in individuals with normal 13q loci. Both genes in each cell must be mutated and because the chance of this occurring is less than the chance of one gene mutating in the hereditary form, sporadic retinoblastoma tends to occur in one eye only at a later age.
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