Résumé :
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communication n° 536 Introduction : Myotonic dystrophy type 1 (DM1) and type 2 (DM2) are caused by a noncoding (CTG)n and (CCTG)n expansion mutation respectively. Both disorders are characterized by nuclear sequestration of mutant CUG-containing RNA that play a fundamental role in the disease pathogenesis. Whereas genetic diagnosis of DM1 is routinely available, limitations in conventional molecular genetic methods for DM2 mutation demonstration have been encountered. Recently, in situ hybridization have been reported as a new approach for the detection of DM2 mutation. Objective : To evaluate the feasibility and efficiency of in situ hybridization for routine molecular diagnosis of DM2. Methods : Chromogenic in situ hybridization (CISH) have been performed in frozen and paraffin embedded biopsy specimen of patients from one of the following groups: (1) DM2 mutation evidenced by molecular genetic tests, (2)DM2 mutation excluded, (3) positive DM1 mutation, (4) normal control with no available genetic test. Results : CISH methods have been optimized to give similar level of nuclear mutant DM2 transcript detection in paraffin-embedded and in frozen skeletal muscle biopsy specimen. This allowed us the retrospective positive confirmation of DM2 in ancient specimen up to 17 years of age. Furthermore, we have observed a positive nuclear signal in cells from various tissues, including skin and smooth muscle. All patients with previously identified DM2 mutation were positive for CISH, whereas no nuclear signal was observed in DM1 patients and controls. Conclusion : Targeting mutant transcripts in tissue section by in situ hybridization approach seems to represent a valuable tool for molecular diagnosis of DM2.
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