MDF Magazine Issue 72 December 2023

Question: My neurologist has diagnosed me with muscular
dystrophy. How do I genetically confirm the diagnosis and
establish the whole process of whom to contact, what the
test involves, pre- and post-test counselling and interpretation
of the results?
What is genetic testing?
Genetic testing is a type of medical test that aims to identify
the exact changes in our genes that cause disease. It is usually
performed by studying DNA – the genetic code that provides
the instruction manual to our body. There are many different
genetic tests – they differ in which genes are tested, how
many are tested at a time, and technically what type of test is
used (depending on the types of genetic faults being looked
for).
Why should I have genetic testing?
The results of a genetic test can confirm a suspected genetic
condition (diagnostic testing). Once a genetic diagnosis is confirmed,
there may be more specific management and therapy
that can be provided. Increasingly therapies are becoming
available, which require the exact genetic diagnosis to be defined.
Patients with different genetic faults may qualify for
different therapies.
Many patients and their families ask about other family members
developing similar symptoms to the individual with the
muscular dystrophy. Accurate information can be provided
only once the genetic diagnosis has been determined in the
affected individual, as conditions which look similar clinically
may have different inheritance patterns and thus different
risks.
Some tests may be able to predict whether an individual is
likely to manifest a condition that is present in their family
(predictive or preclinical testing) before the person has symptoms.
The tests may also be used to determine if an individual
is a silent carrier of a condition and whether the person is at
risk of having an affected child.
What genetic tests are available?
Many different genetic tests are available. They are complex
and need to be individualised for different people, based on a
combination of the clinical features present and the family
history. They can also be expensive. Even if two unrelated
individuals appear to have the same genetic condition, the
cause may be a fault in different genes or there may be many
different faults in the same gene. Different tests may be required
to identify the faults.
Newer genetic tests allow us to test many genes in parallel (in
a so-called gene panel) rather than one at a time. At present
these tests generally provide good options to reach a clear
answer. In some cases, where the clinical picture is more
distinct, it may be better to test a single gene in depth. No
panel covers all genes and/or genetic variants, so importantly
the best test has to be selected for each patient. Unfortunately,
genetic tests are still not perfect and may still not provide
answers or may provide results which are difficult to interpret.
Negative tests exclude certain conditions but do not exclude
a genetic issue.
Who should perform genetic testing?
Testing should be performed in consultation with a medical
geneticist or genetic counsellor, who can help to select the
test most appropriate for the patient and most likely to provide
the required information. Such health professionals
would be able to explain the value and limitations of genetic
testing for that individual. They would also be able to help in
interpreting results and advising on further management and
on risks to other family members.
“Start by doing what’s necessary; then do what’s possible; and suddenly you are
doing the impossible.”
-Francis of Assisi