Cross-Canada availability
Genetic tests are available from genetics clinics in most provinces for more than 25 adult-onset disorders including hereditary breast, ovarian and colon cancer, Huntington's disease and an inherited form of early onset Alzheimer's. Genetic clinics can also test for hemochromatosis, an iron overload disorder, and rarer conditions, such as inherited blood clotting disorders. Tests for more than 100 genetic disorders affecting newborns and young children can be offered to prospective parents, pregnant moms and newborns.
Most genetic tests offered to adults today are for diseases caused by a mutation in a single gene inherited from only one parent. These are known as autosomal dominant disorders. This pattern of inheritance is important to recognize; if several close relatives on one side of your family (maternal or paternal) have been diagnosed with the same disorder, such as hereditary breast or colon cancer, you may be a candidate for genetic counselling and possible testing. "People are usually referred to a genetics clinic by a family physician or a specialist," says genetic counsellor Joanne Honeyford, the manager of clinical services for the North York General genetics program. If you think you might be a candidate, see your family doctor for a referral. Before you meet with a genetic counsellor or medical geneticist, you will be asked to gather as much pertinent information as possible about the incidence of the disease in your family. How many of your close relatives were affected by the illness? Look at three generations: grandparents, parents, aunts, uncles, siblings and cousins. At what age was each person diagnosed with the disease and what was the outcome? All of this information, with supporting medical records, will be used to construct a family pedigree -- a chart or family tree that provides a detailed picture of the history of the disease in your family.
How a test works, and how to qualify
Your first appointment at the genetics clinic will start with a family history assessment. "A clinical geneticist will determine whether your family history is strong enough to warrant a genetic test," says Martin Somerville, director of the molecular diagnostic laboratory at Stollery Children's Hospital in Edmonton. Genetic tests are only offered to families that meet specific criteria, and each disease has its own criteria.
In the case of Huntington's disease, a diagnosis of the disease in one parent would be sufficient to make you and your siblings eligible for genetic testing. The criteria for breast, ovarian and colon cancer are more complex. If only one close relative was diagnosed with breast cancer, then your family probably wouldn't be eligible for testing. But if your mother, aunt and first cousin were diagnosed with breast or ovarian cancer at a young age, then your family would qualify.
If your family meets the criteria and you wish to have a presymptomatic genetic test, the clinic will first need to test someone in your family who has already been diagnosed with the disease. It could be your mother, sister, aunt or cousin. Starting with an affected person maximizes the chances of finding a mutation in your family since that person is more likely to carry the mutation than you are. So be prepared to ask an affected relative to consider being tested or accompany you to the first appointment.
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