Wednesday 11 January 2012
Research improves diagnosis of facioscapulohumeral muscular dystrophy
Some patients are diagnosed with facioscapulohumeral muscular dystrophy (FSHD) based on their symptoms but this diagnosis can not be confirmed by the usual genetic test. European scientists recently studied several such cases, and their findings suggest alternative diagnoses that doctors should consider when trying to reach a firm decision as to what condition a patient has.
The diagnosis of FSHD is usually straightforward because the muscle groups are affected in a very specific pattern. However, some patients may have symptoms that superficially resemble FSHD, but is actually a different condition. Even the most experienced clinician can sometimes be fooled by such 'look-alike' cases.
Finding alternative explanations
Most of the time, a diagnosis of FSHD can be confirmed by a genetic test: more than 90 percent of patients have a deletion of a piece of DNA on chromosome 4. However, in a small subset of cases (5 to 10 percent) this mutation is not observed. In a recent European study, scientists investigated 16 such patients who had FSHD-like symptoms, but an intact chromosome 4.
Upon closer inspection, half of the patients were confirmed to have FSHD after all, albeit of a more complicated type. However, six of the other patients turned out to have different muscular dystrophies: they were tested for mutations in several other genes known to be involved in other conditions, which led to a new diagnosis. Four of them actually have limb-girdle muscular dystrophy type 2A. Two others carry mutations in a gene called 'valosin-containing protein', which is associated with several other muscular disorders.
What does this mean for patients?
These findings have important implications for the small group of patients for whom adiagnosis of FSHD can not be confirmed by a genetic test. In these cases, doctors should consider alternative genetic tests for other muscle disorders that can mimic FSHD-like symptoms.
Reaching a confirmed diagnosis is important as it gives patients a clearer idea as to how their condition might progress allowing them to plan for the future. A genetic diagnosis also opens up opportunities for genetic testing of family members and allows family planning decisions to be made. In some cases prenatal testing and preimplantation genetic diagnosis may be available to avoid passing the condition onto future generations.
Importantly a confirmed genetic diagnosis is required for participation in most clinical trials and to access any new treatments that may become available in the future. This is because although the resulting symptoms may be similar, different genetic mutations cause different problems in the muscle that are usually only treatable by specific medications. This is especially true for gene therapies that aim to replace or repair the defective gene.
In this study, only three other genes were tested. In the coming years, it will be possible to look at the more than 20, 000 genes in the human body with a single test - this is known as next generation DNA sequencing. This will mean quicker, more accurate genetic diagnostics for many patients.
Further information and links
Read about next generation DNA sequencing in Target Research magazine.
The full original paper was published in the Journal of Medical Genetics and is available for free through our partnership with Patient Inform. The article is written in technical language with no summary in layman's terms. Click here to access the full article.
Find out about the FSHD research we fund.
Many thanks to Andreas Leidenroth for writing this research summary. Andreas is a Muscular Dystrophy Campaign-funded PhD student researching FSHD in Nottingham.
If you have any questions about this or any other research please contact us: research@muscular-dystrophy.org.
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