Genetic testing is used to determine if
your genes have variances that might
cause a disease.
The genes that determine everything
from the colour of your eyes to the curl in
your hair are found in the 23
chromosome pairs in your cells. You
inherit half your chromosomes from your
mother and half from your father. Genes
are made up of DNA and sometimes
contain small variations, called
mutations, which may or may not lead to
a health problem. Everyone’s genes carry
some normal variances.
In genetic testing, a blood sample is
taken and the DNA sequence studied
for a specific gene mutation to diagnose
a health concern. In predictive genetic
testing, an individual who has no
signs of a genetic condition is tested
for a particular gene change. Test
results usually take several weeks or
months, but may be available sooner
if the situation is urgent or a mutation
has been found previously in a family
member. Most predictive test results
show probabilities of increased risk—
even a positive result does not guarantee
a person will become sick. Some
tests can be difficult to interpret and
none are 100 per cent determinative.
Genetic counselling is an important
part of helping people understand the
complexities of what testing can mean
and how to deal with the results.
What is genetic testing?
pre-symptomatically ill, describes people who have
tested positive and are not sick, but start to perceive
themselves as ill or becoming ill down the road.
And testing negative can still be emotional.
A person who screens negative, while another
family member is diagnosed with a disease, often
experiences survivor’s guilt. Instead of feeling
relief, the one spared feels undue remorse, or
Tara Johnson-Ouellette was sure she wouldn’t
feel guilty if she tested negative for Huntington
disease, an inherited brain disorder that affects one
in every 10,000 Canadians. In 1994, when she
was 20, her mother was diagnosed—a year after
researchers 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.
she felt vanished on the short ride home from the
hospital, and guilt assumed its place when she told
her dying mother the good news.
She says her brother, who was too young to be
tested in 1994, has never wanted to know if he
carries the gene. While carrier screening may be
offered to other family members after a diagnosis,
Seavilleklein stresses it’s very important for siblings
to 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 and
director of the Genetic Laboratory in Edmonton,
which tests for about 40 different genetic
disorders. For adults, the most commonly ordered
tests are cystic fibrosis, hemochromotosis (iron
overload), Huntington’s disease, amyotrophic lateral
sclerosis (ALS, or Lou Gehrig’s Disease), deafness
and colon cancer.
Hume says a person is susceptible to developing
hereditary breast or ovarian cancer when they
inherit a mutation in either their BRCA1 or BRCA2
gene. The BRCA genes are the ones responsible
are born with one mutated gene, you have a 50
to 70 per cent chance of acquiring the second
like Docherty’s cousin, may acquire the second
mutation early, while others, like Docherty’s
mother, 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