Genetic testing is used to determine ifyour genes have variances that mightcause a disease.
The genes that determine everythingfrom the colour of your eyes to the curl inyour hair are found in the 23chromosome pairs in your cells. Youinherit half your chromosomes from yourmother and half from your father. Genesare made up of DNA and sometimescontain small variations, calledmutations, which may or may not lead toa health problem. Everyone’s genes carrysome normal variances.
In genetic testing, a blood sample istaken and the DNA sequence studiedfor a specific gene mutation to diagnosea health concern. In predictive genetictesting, an individual who has nosigns of a genetic condition is testedfor a particular gene change. Testresults usually take several weeks ormonths, but may be available soonerif the situation is urgent or a mutationhas been found previously in a familymember. Most predictive test resultsshow probabilities of increased risk—even a positive result does not guaranteea person will become sick. Sometests can be difficult to interpret andnone are 100 per cent determinative.
Genetic counselling is an importantpart of helping people understand thecomplexities of what testing can meanand how to deal with the results.
What is genetic testing?
pre-symptomatically ill, describes people who havetested positive and are not sick, but start to perceivethemselves as ill or becoming ill down the road.
And testing negative can still be emotional.
A person who screens negative, while anotherfamily member is diagnosed with a disease, oftenexperiences survivor’s guilt. Instead of feelingrelief, the one spared feels undue remorse, oreven responsibility.
Tara Johnson-Ouellette was sure she wouldn’tfeel guilty if she tested negative for Huntingtondisease, an inherited brain disorder that affects onein every 10,000 Canadians. In 1994, when shewas 20, her mother was diagnosed—a year afterresearchers had isolated the mutant gene. Johnson-Ouellete had a 50/50 chance of inheriting the gene.
recalls Johnson-Ouellete, whose family became
the first in Calgary to receive the new protocol
regarding genetic counselling for Huntington’s
cure, and by the way, you’re at risk. I didn’t think it
Johnson-Ouellete was prepared for the worst
when the results came back nine months later.
It;was;not;what;I;expected.”;But;the;immediate;reliefshe felt vanished on the short ride home from thehospital, and guilt assumed its place when she toldher dying mother the good news.
She says her brother, who was too young to betested in 1994, has never wanted to know if hecarries the gene. While carrier screening may beoffered to other family members after a diagnosis,Seavilleklein stresses it’s very important for siblingsto decide for themselves if they want to be tested,and to get separate counselling.
Although the decision to test for a genetic
disease is yours alone, Babu emphasizes, you
don’t have to make it alone. Before a hereditary
cancer genetic test is arranged, an adult without
symptoms is referred to a genetics clinic for
genetic counselling to help understand the risks,
benefits and limitations of testing. In Alberta, only a
genetic counsellor or clinical geneticist can order a
hereditary cancer genetic test.
Dr. Stacey Hume is a molecular geneticist anddirector of the Genetic Laboratory in Edmonton,which tests for about 40 different geneticdisorders. For adults, the most commonly orderedtests are cystic fibrosis, hemochromotosis (ironoverload), Huntington’s disease, amyotrophic lateralsclerosis (ALS, or Lou Gehrig’s Disease), deafnessand colon cancer.
Hume says a person is susceptible to developinghereditary breast or ovarian cancer when theyinherit a mutation in either their BRCA1 or BRCA2gene. The BRCA genes are the ones responsiblefor;controlling;cell;growth;in;the;body.;“If;youare born with one mutated gene, you have a 50to 70 per cent chance of acquiring the secondmutation;and;developing;cancer;by;age;70.”;Some,like Docherty’s cousin, may acquire the secondmutation early, while others, like Docherty’smother, may never acquire it.
Through genetic counselling, Babu helps
individuals do what is important to them. That
includes ensuring the motivation to test is from
the individual and not someone else. Pressure
from concerned family members is common with
until I’ve helped someone make a decision to test
—or not test—that is consistent with their own
personal life values and priorities. These are not
Making the decision involves understanding
options and implications. Docherty knew if she
tested positive for breast cancer, she could choose
increased cancer screening or preventive surgery.
Just knowing you are
more susceptible to disease
can significantly alter your health