BRCA 1 & 2 Mutations: 

A small percentage of people (about one in 400, or 0.25% of the population) carry mutated BRCA1 or BRCA2 genes. A BRCA mutation occurs when the DNA that makes up the gene becomes damaged in some way.

When a BRCA gene is mutated, it may no longer be effective at repairing broken DNA and helping to prevent breast cancer. Because of this, people with a BRCA gene mutation are more likely to develop breast cancer, and more likely to develop cancer at a younger age. The carrier of the mutated gene can also pass a gene mutation down to his or her offspring.
The following mutations also increase your cancer risk:

ATM | BARD1 | BRIP1 | CDH1 | CHEK2 | MRE11A | MSH6 | NBN | PALB2 | PMS2 | PTEN | SEC23B | RAD50 | RAD51C | STK11 | TP53

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