Some With MG Have Autoimmunity-Related Protein Variant

According to a report in the February issue of Annals of Neurology, a variant form of the gene for the protein PTPN22 may increase susceptibility to at least one type of myasthenia gravis (MG). PTPN22 is thought to have regulatory functions in the immune system.

In MG, an autoimmune disease, the immune system mistakenly attacks muscle cells and interferes with their ability to receive signals from nerve cells. Ninety percent of MG patients make antibodies that attack the Ach receptors, where chemical nerve signals normally land.

In December, Torkel Vang at the Burnham Institute in La Jolla, Calif., and colleagues reported that the PTPN22 variant may predispose people to autoimmune disease in general (see “Protein Variant May Be Autoimmune Disease Risk Factor.”)

Now, Claire Vandiedonck of INSERM-Paris-Descartes University in France and colleagues at several other French institutions, have found a strong association of the variant with one type of MG.

The investigators studied 470 people with MG and 296 without the disease. They categorized the MG patients depending on whether or not they had a thymus tumor (thymoma), present in some MG patients; and whether or not they were producing antibodies to a protein called titin, which some MG patients make in addition to their Ach receptor antibodies.

Of the 293 people studied who had MG but did not have a thymoma or antibodies to titin, 80 (13.7 percent) had the suspect PTPN22 variant. In two other MG groups, about 10 percent had it; and in the non-MG group, it was there in only 7.4 percent.

The authors say their finding supports the idea that MG is more than one disease and provides a valuable lead for further investigations.