A team of researchers, including Lisa Rider, MD, clinical professor of medicine at the George Washington University School of Medicine and Health Sciences (SMHS) and head of the Environmental Autoimmunity Group at the National Institutes of Health National Institute of Environmental Health Sciences; Gulnara Mamyrova, MD, PhD, assistant research professor of medicine at SMHS; and Rodolfo Curiel, MD, associate professor of medicine at SMHS, determined that anti-MDA5 autoantibodies associated with juvenile dermatomyositis (JIIM) are a distinct phenotype in North America.

Autoantibodies from myositis, or inflammation of the muscles, have defined specific phenotypes, or groups, of patients with juvenile myositis. To assess if other autoantibodies, rather than those specific to myositis, could define phenotypes, the research team examined the characteristics of 35 JIIM patients with anti-MDA5 autoantibodies, otherwise known as anti-melanoma differentiation-associated gene 5. The researchers also evaluated differences from other myositis-specific autoantibody groups.

“Our results indicated that anti-MDA5 autoantibodies were present in 7.7% of JIIM patients,” Rider said. “This presence was associated with various factors, including older age at diagnosis and lower serum creatine kinase and aldolase levels. These patients had more frequent weight loss, adenopathy, arthritis, interstitial lung disease, and less frequent falling than other patient phenotypes.”

In comparing anti-MDA5 patients to those with anti-transcriptional intermediary factor 1 (TIF1), anti-nuclear matrix protein 2, and myositis-specific autoantibody/myositis-associated autoantibody-negative, the researchers noticed additional differences. This study is among the first to compare the features of these myositis autoantibody groups directly.

“Anti-MDA5 patients received fewer medications, and corticosteroid treatment was shorter compared with anti-TIF1 and anti-nuclear matrix protein 2 autoantibody groups,” Rider explained. “The frequency of remission was higher in anti-MDA5 than anti-synthetase autoantibody-positive JIIM. In addition, in multivariable analyses, weight loss, arthritis, and arthralgia were most strongly associated with anti-MDA5 autoantibody-positive JIIM.”

Mamyrova and Curiel collaborated with researchers from the National Institute of Environmental Health Sciences at the National Institutes of Health, Oklahoma-based Veteran’s Affairs Medical Center, University of Oklahoma Health Sciences Center, and Oklahoma Medical Research Foundation, as well as IWK Health Centre and Dalhousie University in Canada.

The study, “Anti-MDA5 Autoantibodies Associated with Juvenile Dermatomyositis Constitute a Distinct Phenotype in North America,” appears in Rheumatology.