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Genetics
Overview
DNA (deoxyribonucleic acid), a
chemical found on cell chromosomes, is responsible for carrying genetic information.
Chromosomes are threadlike structures present within the nuclei of cells. DNA’s
double helix structure allows the chromosomes to be replicated during cell division. Genes
(segments of DNA) contain instructions for controlling when cells should grow, divide, and
die. Certain genes called tumor suppressors slow down the process of cell division,
causing cells to die.
Changes in DNA can sometimes cause
normal cells to become cancerous by de-activating the tumor suppressor genes. Researchers
are still investigating how and why some genes mutate but have discovered that inherited
DNA changes may cause cancers to occur more frequently in some families. However, most DNA
mutations that cause breast cancer are not inherited; they occur during a woman’s
life and may be caused by a variety of factors (many still unknown to medical experts).
These factors may include exposure to certain chemicals (such as Aldrin, Alachlor, and
Acetamide), high dose radiation (from atomic bombs or from certain types of radiation therapy used to treat other cancers), other
environmental exposures, diet, and smoking.
BRCA1 (breast cancer gene 1) and BRCA2
(breast cancer gene 2) are two tumor suppressor genes that, when functioning normally,
help repair damage to DNA (a process that also prevents tumor development). In 1994,
researchers discovered that women who carry mutations of BRCA1 or BRCA2 are at higher risk
of developing both breast and ovarian cancer than women who do not have these genetic
mutations. Currently, women with BRCA1 mutations account for 5% of all breast cancer
cases.
Dr. Sandhya Pruthi, MD, a Breast Health
Specialist at the Mayo Clinic, estimates that 20% of women who carry BRCA1 mutations will
develop breast cancer by age forty, 51% by age fifty, and 87% by age sixty.
How do
physicians test for BRCA mutations?
To test for BRCA1 or BRCA2
mutations, a small sample of blood is drawn, and the DNA is analyzed for BRCA defects. In
addition to being at higher risk for developing breast cancer, women who test positive for
BRCA defects are at a 20% to 60% greater risk of developing ovarian cancer. BRCA1
mutations may also lead to a higher lifetime risk of colon or prostate cancer, while BRCA2
mutations may raise lifetime risk of these and possibly other cancers.(1)
Presently, there are over 2000
genetic mutations associated with BRCA1 and BRCA2 genes. Women who test positive for BRCA
defects will not necessarily develop breast cancer; they are merely at higher risk for the
disease. Additionally, not all BRCA mutations carry the same risk of cancer. A new study
conducted at Baylor College in Texas reveals that the protein ATM (ataxia telangiectasia)
might be linked to breast cancer development in women who test positive for a mutated
BRCA1 gene. Click here to learn more about the ATM protein
study.
Who should consider genetic testing?
BRCA1 and BRCA2 genetic testing is
a controversial topic among health care professionals. At many clinics, only women whose
family histories place them at high risk of developing breast or ovarian cancers are
eligible for genetic testing. Any woman considering genetic testing should discuss the
process with a physician, nurse, or genetic counselor before proceeding with the testing.
| Women
at high risk of developing breast cancer may wish to consider genetic testing for mutated
BRCA genes. |
Both men and women may
inherit and pass on BRCA1 or BRCA2 mutations. According to the Mayo Clinic, families that
typically pass on BRCA defects have the following characteristics:
- Breast cancer in two or more close
relatives, such as a mother and two sisters
- Early onset of breast cancer in family
members, often before age fifty
- History of breast cancer in more than
one generation
- Cancer in both breasts in one or more
family members
- Frequent occurrence of ovarian cancer
- Eastern and Central European (Ashkenazi)
Jewish ancestry, with a family history of breast and/or ovarian cancer (researchers have
identified two types of BRCA1 mutations and one BRCA2 mutation that are especially
prominent in this group)
Genetic testing raises some
complicated questions women should ask themselves before being tested. Genetic counselors
can be very helpful.
| Women considering having their blood
analyzed for genetic risk factors are encouraged to discuss their situation with a
physician or genetics counselor before testing begins. |
- Would I want to know that I am at risk
of developing a potentially life-threatening disease?
- How will knowing I am at increased risk
of breast cancer change me emotionally?
- What can be done if I find out I may
develop a potentially life-threatening disease?
- If I test positive for a BRCA mutation
(i.e., an increased risk of breast cancer), should my children be tested?
- How will my family react if I test
positive for a BRCA mutation?
- How will the female members of my family
react if I find out I am at increased risk for breast cancer? Should they consider genetic
testing too?
- How will the results of my genetic tests
be used by physicians?
- What are the long term effects in terms
of insurance coverage if you are found to carry the BRCA mutation?
Click here to
learn more about candidates for BRCA gene testing.
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