[IgG subclasses in the patients with myotonic dystrophy].

Low serum concentration of IgG in myotonic dystrophy (MyD) has been well documented and has been considered to be due to accelerated breakdown of IgG. However, the catabolic rate of IgG is tightly regulated by serum IgG level and basal metabolic rate. The serum IgG level and basal metabolic rate in the patient with MyD is reported to be significantly low. One possible explanation for this fact is presence of disproportion in IgG subclasses; if the level of one or some subclasses is high, catabolism of total IgG could be accelerated regardless of decreased total IgG. In this study, we examined serum concentration of all four IgG subclasses by sandwich ELISA methods in 43 patients with MyD and 24 healthy age- and sex-matched controls. Serum levels of al IgG subclasses were lower in MyD than those in normal controls, especially the levels of IgG1 and IgG3 were significantly low (p < 0.01) as compared to those in normal controls. These results, combined with our previous studies, suggest that accelerated catabolism is inadequate as a cause of low serum concentration of IgG in MyD. Further studies are required to approach the mechanism of low serum concentration of IgG in the patients with MyD.