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Genetic Counselling

Genetic counselling involves close evaluation and discussion of your family history of cancer and personal medical status to explain what role genetic factors may play in your personal risk to develop cancer. The counsellor will explain how cancer risk can be inherited and whether genetic testing could be used to better define your personal cancer risk. Genetic counselling can help you decide if genetic testing is right for you.

Your visit to the clinic will include an estimation of your breast cancer risk. This estimation will initially be based on your family and medical history information. It is done by comparing your family and personal information to that of others that has been published in the cancer risk literature. It is only an estimate but can help us to recommend screening guidelines for you. Some families will qualify for genetic testing for breast cancer genes. This procedure, which looks for altered breast cancer genes, may help to more accurately define your risk for cancer and will be discussed below.

Genes, Chromosomes and Mutations

Genes are the blueprints for the structure and function of our bodies. They are made up of DNA, our genetic material. Genes are carried on string-like structures called chromosomes. We have approximately 100,000 genes located on 23 pairs of chromosomes. We inherit these chromosomes at conception from our parents. One member of each pair of chromosomes comes from our father and one from our mother.

Each gene has a specific function within the body. Some, such as the genes that dictate our eye colour or our gender, contribute to our physical characteristics. Other genes have duties that are invisible to us when they work properly. Examples are the genes that control our metabolism or the rate at which our cells divide.

A gene is a written instruction that tells the body to create a specific protein, which will perform a certain function in the body. Occasionally, a particular gene may lose its ability to function properly due to a process called mutation. A mutated gene is one that has been changed into a form that will create a non-functional protein, or no protein at all. The effect on the body will be different depending on which gene carries the mutation. There are genes that will lead to an increased risk for the development of breast and ovarian cancer if they are inherited in a mutated form. These genes are called breast and ovarian cancer susceptibility genes since they increase the risk for breast and ovarian cancer.

Breast and Ovarian Cancer Susceptibility Genes: BRCA1/2

Presently, we know of two major breast and ovarian cancer susceptibility genes. They are called BRCA1 and BRCA2 (BReast CAncer 1 and 2). They were discovered in 1994 and 1995 respectively.

If a woman inherits a mutated BRCA1 or BRCA2 gene, she will be at an increased risk to develop breast and ovarian cancer. Since not every woman who carries one of these mutated genes will develop cancer, they are called cancer susceptibility or predisposition genes. Depending on which gene has been mutated, there are some additional cancer risks for male mutation carriers. The specific risks for a mutation carrier will be discussed later.

Inherited susceptibility to breast and ovarian cancer is dominantly inherited. All men and women carry two copies of each BRCA gene (one copy of each from each parent). A mutation carrier, by definition, would carry one normal and one mutated copy of the BRCA gene. Each time that individual creates a sperm or egg, exactly one-half of their genetic material is passed on. It is completely random which copy of each gene is passed on to each child. Therefore, each child of a BRCA mutation carrier has a 1 in 2 (50%) chance to have inherited the mutated gene. Likewise, they would have the same chance to inherit the normal gene and therefore not be at an increased risk for cancer.