Comparative transcriptional and biochemical studies in muscle of myotonic dystrophies (DM1 and DM2)

Myotonic dystrophy type 1 (DM1) and myotonic dystrophy type 2 (proximal muscular myopaty/DM2) are caused by similar dynamic mutations at two distinct genetic loci. The two diseases also lead to similar phenotypes but different clinical severity. Dysregulation of alternative splicing has been suggested as the common pathogenic mechanism. Here, we investigate the molecular differences between DM1 and DM2 using reverse transcriptase-polymerase chain reaction of troponin T (TnT) and the insulin receptor (IR), as well as immunoblotting of TnT in muscle biopsies from DM1 and DM2 patients. We found that: (a) slow TnT was encoded by two different transcripts in significantly different ratios in DM1 and DM2 muscles; (b) DM2 muscles exhibited a higher degree of alternative splicing dysregulation for fast TnT transcripts when compared to DM1 muscles; (c) the distribution of TnT proteins was significantly skewed towards higher molecular weight species in both diseases; (d) the RNA for the insulin-independent IR-A isoform was significantly increased and appeared related to the fibre-type composition in the majority of the cases examined. On the whole, these data should give a better insight on pathogenesis of DM1 and DM2.