Active Genes

In a hereditary syndrome/cancer, all the cells of the organism carry the mutation that increases the risk of cancer.

However, the disease usually develops only in one, or a reduced number of organs. For example the syndrome linked to mutations on BRCA genes, tends to affect the breasts, ovaries or prostate.

Why?

The explanation is simple. A mutation is only visible if it affects a cell where the gene is being used.

The DNA works as a kit of instructions. However, each cell only uses those genes/instructions that are necessary for its specific function, with the remaining genes staying inactive. For example, a liver cell and a brain cell are going to have different sets of active and inactive genes.

For this reason, in hereditary cancer the only cells with a high risk of developing the disease – despite all the cells in the organism carrying the mutation – are those that actually use that gene.

This means that the risk of a hereditary cancer is directly proportional to this number of cells, although that is not how disease risk is calculated

For that there is special software, which, for example, has found that a woman with a BRCA1 mutation, which is linked to breast cancer, has 50-80% chances of developing the disease before the age of 70.