For some people with seronegative myasthenia gravis (MG), genetic testing may show that the real cause of their symptoms is not MG but an inherited condition known as congenital myasthenic syndrome (CMS), according to a recent study in the journal Neurology.
Most people with MG can be diagnosed with a blood test that looks for certain antibodies. But about one in 10 people with MG don’t have these antibodies. This is known as seronegative myasthenia gravis (SNMG).
In this study, 50 adults with SNMG from Austrian clinics underwent whole-exome sequencing, a type of advanced genetic testing. Researchers discovered that seven of the patients (14%) actually had CMS, not SNMG.
While MG is an autoimmune disease, CMS is inherited through changes in certain genes. It can look very similar to MG, with symptoms such as drooping eyelids, double vision, muscle weakness or trouble swallowing.
Unlike MG, CMS does not respond well to immune-suppressing medications and may even worsen with them. In this study, most of these patients had already been treated with immune therapies or even had surgery to remove the thymus gland.
Read more about MG testing and diagnosis
The seven patients diagnosed with CMS had changes in genes called CHRNE and RAPSN. The researchers also found a few other patients with possible but uncertain genetic changes, showing that more research is needed. No clear clinical features, such as age of onset or family history, were reliable in predicting who had CMS.
The researchers concluded that “offering genetic testing to patients with SNMG may have profound implications for clinical management,” since identifying CMS can change treatment decisions and improve outcomes. “This may become even more relevant with the emergence of targeted therapies,” they noted.
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