The two BRCA genes are supposed to suppress the growth of tumours. But in some people, they mutate and could cause cells to divide and change more rapidly. This can lead to breast, ovarian and other cancers.
The United States' National Cancer Institute says women with the BRCA mutation have a 45 per cent to 65 per cent risk of getting breast cancer, compared with 12 per cent in the general population; and 11 per cent to 39 per cent would get ovarian cancer, compared with the norm of 1.3 per cent.
Men are not exempt - the mutation puts them at higher risk of getting prostate cancer. Both genders also face higher risks of getting bowel and pancreatic cancers.
These genes are inherited, so once one member of the family has the gene, others should test for it so they can take precautions.
That is why Dr David Tan, a consultant in the department of haematology-oncology at the National University Cancer Institute, Singapore (NCIS), urges women with an immediate family member who has had cancer with the gene mutation to also test for it.
NCIS has been offering the blood test since 2000. It used to charge $1,800 to $2,000, but dropped the price to $700 to $800 a few months ago.
It cannot be paid for with Medisave, but there is help from non-governmental organisations for those who have difficulty paying.