Certain cells from a mother persist in their children’s bodies and can provoke an immune response in which the child’s body attacks itself, according to Mayo Clinic research published in the current issue of the Journal of Immunology (http://www.jimmunol.org). The findings are important not only in seeking the cause and treatments of this disease, but also in understanding an entire class of autoimmune disorders.
Juvenile dermatomyositis (der-mat-o-my-o-SITE-us), or JDM, is a rare muscle-damaging condition that causes a child’s immune system to attack the body, as if it were an invading life form. Muscles deteriorate and the child becomes weak and fragile. There is no cure for JDM. Current treatments include medication, physical therapy and added nutrition.
“The key aspect of our study suggests a mechanism for the disease, and deepens our understanding of autoimmune disorders in general,” says pediatrician and lead investigator Ann Reed, M.D. “And because we studied a larger population of JDM patients and control groups than has ever been studied, we can feel confident in our results.”
Significance of the Mayo Clinic Research
In the largest study of its kind, Mayo Clinic researchers examined 72 JDM patients, with an average age of 10. They compared them to siblings who did not have the disease, as well as to a control group of healthy children. Several key findings emerged:
- Most JDM patients carry a particular gene (labeled HLA) which they received from their mother during pregnancy.
- When a child has the HLA gene on a mother’s cell, it triggers an immune response against the child.
- These cells may be part of the mechanism that causes JDM.
Researchers have known for years that fetal cells can be found in women several years after giving birth. They have thought these may contribute to the development of autoimmune diseases in women during and after their childbearing years. In the current study, the Mayo Clinic group looked at the opposite situation: persistence of maternal cells in children.
In the Mayo Clinic study, 83 percent of JDM patients had cells from their mother. This compares to 23 percent of their unaffected siblings who had maternal cells, and 17 percent of healthy children who had maternal cells in their blood. The presence of this maternal (also called “chimeric”) cell is strongly associated with a particular genetic makeup of the mother. Children with JDM may suffer organ failure in the same way transplant patients often do. Because of this resemblance to a type of organ rejection disease, the Mayo Clinic team investigated the idea that “non-self” or chemeric cells may play a role in initiating JDM.
The Mayo Clinic researchers discovered two new aspects of chimeric cells. First, they remain in the offspring after birth and are related to the HLA genes, and second, chimeric cells are not merely present in the children — but they are active, as shown by the attacks they mount against the child’s body.
About the Disease JDM
JDM causes inflammation of the blood vessels under the muscle and skin. This results in muscle damage, as well as in tissue changes of skin over the eyelids, finger joints and knuckles. Symptoms appear gradually and include: muscle pain and tenderness; difficulty swallowing, which results in weight loss; irritability; fatigue; fever; rash around the eyelids, finger joints, knuckles, elbows, ankles or knees.
Diagnosis may involve blood tests to detect muscle enzymes and markers of inflammation; an electromyography (EMG) to assess nerve or muscle damage; muscle biopsy for examination; X-rays; and MRI. Current treatments include medications to reduce inflammation and skin rashes; physical and occupational therapy to improve muscle function; and nutritional support.
[Reed, A.M., McNallan, K., Wettstein, P., Vehe, R., and Ober, C. (2004). Does HLA-dependent chimerism underlie the pathogenesis of juvenile dermatomyositis? J. Immunol. 172, 5041-5046.]