Myotonic dystrophy type 1 (DM1) is caused by DM protein kinase (DMPK) transcripts containing an expanded (CUG)n repeat. Antisense oligonucleotide (AON)-mediated suppression of these mutant RNAs is considered a promising therapeutic strategy for this severe disorder. Earlier, we identified a 2′-O-methyl (2′-OMe) phosphorothioate (PT)–modified (CAG)7 oligo (PS58), which selectively silences mutant DMPK transcripts through recognition of the abnormally long (CUG)n tract. We present here a comprehensive collection of triplet repeat AONs and found that oligo length and nucleotide chemistry are important determinants for activity. For significant reduction of expanded DMPK mRNAs, a minimal length of five triplets was required. 2′-O,4′-C-ethylene-bridged nucleic acid (ENA)–modified AONs appeared not effective, probably due to lack of nuclear internalization. Selectivity for products from the expanded DMPK allele in patient myoblasts, an important requirement to minimize unwanted side effects, appeared also dependent on AON chemistry. In particular, RNase-H–dependent (CAG)n AONs did not show (CUG)n length specificity. We provide evidence that degradation of long DMPK transcripts induced by PS58-type AONs is an RNase-H independent process, does not involve oligo-intrinsic RNase activity nor does it interfere with splicing of DMPK transcripts. Our collection of triplet repeat AONs forms an important resource for further development of a safe therapy for DM1 and other unstable microsatellite diseases.

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Multiple myeloma is a heterogeneous disease, which is characterized by the occurrence of specific genomic abnormalities that are both of diagnostic and prognostic relevance. Since the detection of these abnormalities through molecular‐genetic techniques is hampered by the overall low percentage of plasma cells present in primary bone marrow aspirates, we assessed the efficacy of these techniques in enriched plasma cell fractions from 61 multiple myeloma patients. Using interphase FISH, genomic abnormalities could be detected in 96% of the enriched samples as compared to 61% in the cultured whole bone marrow samples. We also found that microarray‐based genomic profiling of enriched plasma samples facilitates the detection of additional, possibly clinically relevant, genomic abnormalities. We conclude that the genomic delineation of enriched plasma cells from multiple myeloma patients results in a significantly increased detection rate of clinically relevant genomic abnormalities. In order to facilitate molecular‐genetic data interpretation, we recommend morphological assessment of plasma cell purity after enrichment. © 2012 Wiley Periodicals, Inc.