A. Vihola, M. Sirito, L. L. Bachinski, O. Raheem, M. Screen, T. Suominen, R. Krahe and B. Udd (2013) Neuropathology and Applied Neurobiology39, 390–405

Aims: Myotonic dystrophy types 1 and 2 (DM1 and DM2) are multisystem disorders caused by similar repeat expansion mutations, with similar yet distinct clinical features. Aberrant splicing of multiple effector genes, as well as dysregulation of transcription and translation, has been suggested to underlie different aspects of the complex phenotypes in DM1 and DM2. Ca²⁺ plays a central role in both muscle contraction and control of gene expression, and recent expression profiling studies have indicated major perturbations of the Ca²⁺ signalling pathways in DM. Here we have further investigated the expression of genes and proteins involved in Ca²⁺ metabolism in DM patients, including Ca²⁺ channels and Ca²⁺ binding proteins. Methods: We used patient muscle biopsies to analyse mRNA expression and splicing of genes by microarray expression profiling and RT‐PCR. We studied protein expression by immunohistochemistry and immunoblotting. Results: Most of the genes studied showed mRNA up‐regulation in expression profiling. When analysed by immunohistochemistry the Ca²⁺ release channel ryanodine receptor was reduced in DM1 and DM2, as was calsequestrin 2, a sarcoplasmic reticulum lumen Ca²⁺ storage protein. Abnormal splicing of ATP2A1 was more pronounced in DM2 than DM1. Conclusions: We observed abnormal mRNA and protein expression in DM affecting several proteins involved in Ca²⁺ metabolism, with some differences between DM1 and DM2. Our protein expression studies are suggestive of a post‐transcriptional defect(s) in the myotonic dystrophies.