What is genetic testing?
Genetic testing is a type of medical test that identifies the 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.
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, more specific management and therapy may 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 the possibility of other family members developing similar symptoms to those of the individual with muscular dystrophy. Accurate information can be provided only once the genetic diagnosis is determined, 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). They may also be used to determine if an individual is a silent carrier of a condition and whether they are at risk of having an affected child.
What genetic tests are available for people with facioscapulohumeral muscular dystrophy (FSHD) and limb-girdle muscular dystrophy (LGMD)?
FSHD and LGMD have some overlapping clinical features but illustrate some important principles in genetic testing.
FSHD is caused by a complex genetic alteration. The testing requires a laboratory with specific expertise in FSHD to do the analysis. FSHD testing is usually done as a single test for this condition. A positive test confirms the diagnosis, and a negative result makes it very unlikely that the condition is FSHD.
LGMD is a large, complex group of conditions with variable but overlapping clinical features. There are over 30 genetic subtypes, each of which may be caused by faults in different genes. Thus, in 2019, if a diagnosis of LGMD is suspected, the most appropriate genetic test would be the so-called gene-panel test, where many genes are analysed simultaneously in order to find the single disease causing a fault in an individual. Such analysis has not always been available but is increasingly available now with newer genetic testing techniques. Such tests may miss specific conditions like FSHD.
It is important to emphasise that genetic testing is complex and expensive. It should be individualised and performed through a medical geneticist or genetic counsellor, who can help to select the test most appropriate for the patient and is most likely to provide the required information. Such health professionals would be able to explain the value and limitations of genetic testing for any individual.