Breast cancer

Breast cancer is common - it affects one in 11 women - so, in most cases, a family history of the illness does not mean it is inherited. But 5-10 per cent of affected women do have an inherited form of the disease, usually with earlier onset. Scientists have identified two genes that are altered: BRCA1 and BRCA2. These genes normally make proteins that repair DNA damage, preventing abnormal cell growth. A woman who inherits a changed version of either of these genes has a high risk of developing breast cancer.

DNA analysis for breast cancer. Each lane shows a different person's DNA. The arrows point to a mutation in the DNA of one patient. St George's Hospital Medical School.