PHOENIX – New therapies are on the horizon for genetic neuromuscular diseases, and this will raise both hopes for patients and challenges for neurologists. , according to Nicolas Madigan, MBBCh, PhD, who spoke at the 2023 annual meeting of the American Association for Neuromuscular and Electrodiagnostic Medicine (AANEM).
“I think we will very soon be in a position to tell these patients that they might actually have a better treatment outcome with a genetic treatment than if they had a sporadic or inflammatory disorder,” said Dr. Madigan, who is an assistant professor of clinical research at Mayo Clinic, Rochester, N.Y.
To illustrate how genetic therapies are changing neurology practice, Dr. Madigan focused his talk on CMT neuropathy, which is the most common hereditary neuropathy and, as a result, has become a prime focus of gene therapy development. “In a city of about a million people, there will be 100-800 patients with one of these disorders,” said Dr. Madigan.
Case report illustrates a change in approach
There are more than 100 known genes that can contribute to CMT, but about 90% of patients harbor alterations in one of four genes: PMP22, GJB1, MFN2, and MPZ.
The trick is determining which patients are candidates for genetic testing, according to Dr. Madigan. He presented a case report of a 39-year-old woman who had experienced sensory symptoms for years, with a sudden exacerbation along with allodynia following COVID-19 vaccination. Her cerebrospinal fluid protein was high and outside electromyography indicated mild demyelinating neuropathy, consistent with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). After her insurance denied IVIG treatment, she received solumedrol, but her symptoms worsened and she was referred to Dr. Madigan.
After 6 months of methotrexate treatment, her sensory symptoms had not improved, and she was referred for genetic testing, which revealed a truncating mutation of the MPZ gene. “What I learned from this case really was that, in a young patient with conduction slowing, you might be considering CIDP. It might actually be better to do genetic testing first as opposed to starting inflammatory neuropathy type treatments with respect to cost – the genetic tests costs $300 versus tens of thousands of dollars for IVIG – and for [patient] welfare as well,” said Dr. Madigan.
Specifically, when clinical signs point to inherited neuropathy and there is conduction slowing, “the biggest bang for your buck might to be to go straight to PMP22 deletion or duplication testing and see if you can get a diagnosis. If that is negative or the clinical features are not as you might suspect, then, if you have other supportive features such as a very young age or there’s predominance of motor or sensory symptoms, you could test more broadly with a panel. If both of these are negative, then you could consider exome sequencing if the clinical phenotype really is consistent with that,” said Dr. Madigan.