Tuesday, May 29, 2007

New Sporadic Breast Cancer Genes Identified

As more genes are identified, tests will become more predictive.

Douglas Easton, University of Cambridge

They identified 30 differences in single DNA bases that seemed to be linked to the disease. These were then compared in more than 20,000 women with breast cancer and in a similar number of controls. The results are reported in Nature1.

Reviews Genetics 1, 40-47 (2000); doi:10.1038/35049558


Germline base substitution mutations occur more frequently in males than in females, especially in older males.
The main explanation for the sex and age effect is that a much larger number of germline divisions occurs in the male than in the female, and continues throughout male adulthood.
Point mutations at some loci occur almost exclusively in males, whereas others have a smaller excess, roughly ten times more than in females. Which is more typical remains to be determined.
For mutations other than point mutations, sex biases in the mutation rate are very variable. However, small deletions are more frequent in females.
The total rate of new deleterious mutations for all genes is estimated to be about three per zygote. This value is uncertain, but it is likely that the number is greater than one.
It is suggested that quasi-truncation selection is the principal explanation for how the population can rid itself of a large number of mutations with a relatively low fitness cost.
Since this form of selection is effective only with sexual reproduction, perhaps the fact that humans reproduce sexually has made it possible to have such a long life cycle.


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