Immunoglobulin abnormalities in patients with myotonic dystrophy.

In order to further investigate immunoglobulin (Ig) abnormalities in patients with myotonic dystrophy (MyD), we examined 65 patients with MyD for their serum concentration of IgG in relation to their immunological functions as well as other clinical and laboratory findings. Turnover of IgG was also examined. We found significant and selective reduction of serum IgG in patients with MyD. The serum concentration of IgG in patients with MyD had a significant negative correlation with duration of illness, which suggested that serum IgG levels in MyD decreased constantly throughout the disease course. Peripheral blood lymphocyte subpopulations, including functional T cell subsets, in vitro lymphocyte proliferation, and in vitro IgG production were normal. The plasma cell population in bone marrow was also normal. The IgG turnover study using 125I-labelled IgG as a tracer revealed an increased extravascular IgG pool, and an increased capillary permeability of intravascular IgG into the extravascular compartment, in patients with MyD. These observations suggested that the Ig abnormalities in patients with MyD were not due to a broader immunological derangements as previously postulated by other authors. The abnormal distribution of IgG is a possible factor leading to reduced serum concentration of IgG in patients with MyD.