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.