Accelerated breakdown of immunoglobulin G (IgG) in myotonic dystrophy: a hereditary error of immunoglobulin catabolism.

Myotonic dystrophy is a hereditary progressive muscular abnormality with dominant transmittance that was first proposed as a separate entity by Batten and Gibb (1) and by Steinert (2) in 1909. The muscular abnormality that is the dominant feature of the disease is characterized by weakness, wasting, and myotonia, especially of the facial, neck, and distal musculature. Other abnormalities frequently associated with the disease include frontal alopecia, cataracts, gonadal atrophy, low basal metabolic rate with normal thyroid function, impaired glucose tolerance, and electrocardiographic abnormalities. Reduction in serum y-globulin concentration has been observed in patients with myotonic dystrophy by some workers (3, 4) but not by others (5). In 1956 Zinneman and Rotstein reported decreased y-globulins in 7 of 12 patients with myotonic dystrophy (6). It was found that the survival halftime of 1311-labeled y-globulin in six of these patients averaged 7.6 days compared to 10.5 days in controls, whereas the survival of albumin-'31I averaged 10.2 days compared to 9.6 days in controls. In recent years, the plasma proteins that possess immunologic activity have been the subject of intensive study. These proteins as a group are referred to as immunoglobulins and can be divided into at least three major classes. These are IgG (7 S y2-globulins), IgA (,82A-globulins), and IgM (yi-macroglobulins or f82M-globulins). Each of these fractions possesses antibody activity and cer-