[Correlation between CTG triplet repeat length and the extent of multisystesmic disorders in myotonic dystrophy]

We investigated whether the degree of (CTG)n expansions is correlated with the extent of multisystemic disorders in 40 patients with myotonic dystrophy (DM). We examined the endocrinological disorders with both the Ellsworth-Howard(EH) test and thyrotropin releasing hormone (TRH) tolerance test. His-ventricular(HV) interval on the His bundle electrogram was analyzed as one of the cardiac conduction disorders. Serum IgG levels and the proliferative response of lymphocyte to concanavalin(Con). A mitogen were investigated as the immunological disorders and both intelligence quotient (IQ) and apnea index(AI) also as the disorders of central nervous systems. Moreover, the extent of muscular involvement was evaluated by muscle disability score, horizontal saccadic velocity using ENG, myopathy index(MI) estimated by quantitative EMG, and pulmonary function test consisting of % vital capacity (% VC) and peak flow. Southern blot were made of the DNAs as described previously. Briefly, the genomic DNAs extracted from the leukocytes were digested with Eco RI then hybridized with a 32P-labeled cDNA25 probe. The results of the EH test (p < 0.05), TRH tolerance test (p < 0.01), HV interval (p < 0.01), serum IgG levels (p < 0.05), and the proliferative response to Con A mitogen (p < 0.01) were all significantly correlated with (CTG)n length. The values of AI (p < 0.01) and IQ (p < 0.01) were significantly correlated with (CTG)n length. In addition, the extent of muscular involvement based on the disability score (p < 0.001), horizontal saccadic velocity (p < 0.001). MIs of Tibialis anterior (p < 0.05), and Biceps brachii (p < 0.02), % VC (p < 0.05) and peak flow (p < 0.01) also was significantly correlated with (CTG)n length. From the above results, it was considered that (CTG)n length was well correlated with disease severity in DM.