Genetics

http://www.breastcancer.org/risk/factors/genetics

About 5% to 10% of breast cancers are thought to be hereditary, caused by abnormal genes passed from parent to child.

Genes are short segments of DNA (deoxyribonucleic acid) found in chromosomes. DNA contains the instructions for building proteins. And proteins control the structure and function of all the cells that make up your body.

Think of your genes as an instruction manual for cell growth and function. Abnormalities in the DNA are like typographical errors. They may provide the wrong set of instructions, leading to faulty cell growth or function. In any one person, if there is an error in a gene, that same mistake will appear in all the cells that contain the same gene. This is like having an instruction manual in which all the copies have the same typographical error.

BRCA1 and BRCA2 genes

Most inherited cases of breast cancer are associated with two abnormal genes: BRCA1 (BReast CAncer gene one) and BRCA2 (BReast CAncer gene two).

Everyone has BRCA1 and BRCA2 genes. The function of the BRCA genes is to repair cell damage and keep breast, ovarian, and other cells growing normally. But when these genes contain abnormalities or mutations that are passed from generation to generation, the genes don’t function normally and breast, ovarian, and other cancer risk increases. Abnormal BRCA1 and BRCA2 genes may account for up to 10% of all breast cancers, or 1 out of every 10 cases.

Having an abnormal BRCA1 or BRCA2 gene doesn’t mean you will be diagnosed with breast cancer. Researchers are learning that other mutations in pieces of chromosomes — called SNPs (single nucleotide polymorphisms) — may be linked to higher breast cancer risk in women with an abnormal BRCA1 gene as well as women who didn’t inherit an abnormal breast cancer gene.

Women who are diagnosed with breast cancer and have an abnormal …

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