title: Molecular, clinical, and muscle studies in myotonic dystrophy type 1 (DM1) associated with novel variant CCG expansions.
abstract: We assessed clinical, molecular and muscle histopathological features in five unrelated Italian DM1 patients carrying novel variant pathological expansions containing CCG interruptions within the 3'-end of the CTG array at the DMPK locus, detected by bidirectional triplet primed PCR (TP-PCR) and sequencing. Three patients had a negative DM1 testing by routine long-range PCR; the other two patients were identified among 100 unrelated DM1 cases and re-evaluated to estimate the prevalence of variant expansions. The overall prevalence was 4.8 % in our study cohort. There were no major clinical differences between variant and non-variant DM1 patients, except for cognitive involvement. Muscle RNA-FISH, immunofluorescence for MBNL1 and RT-PCR analysis documented the presence of ribonuclear inclusions, their co-localization with MBNL1, and an aberrant splicing pattern involved in DM1 pathogenesis, without any obvious differences between variant and non-variant DM1 patients. Therefore, this study shows that the CCG interruptions at the 3'-end of expanded DMPK alleles do not produce qualitative effects on the RNA-mediated toxic gain-of-function in DM1 muscle tissues. Finally, our results support the conclusion that different patterns of CCG interruptions within the CTG array could modulate the DM1 clinical phenotype, variably affecting the mutational dynamics of the variant repeat.
authors.affiliation: Fondazione Don Carlo Gnocchi, ONLUS, Milan, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Santoro
authors.forename: Marcella
authors.initials: M
authors.lastname: Masciullo
authors.forename: Roberta
authors.initials: R
authors.lastname: Pietrobono
authors.forename: Giulia
authors.initials: G
authors.lastname: Conte
authors.forename: Anna
authors.initials: A
authors.lastname: Modoni
authors.forename: Maria Laura E
authors.initials: ML
authors.lastname: Bianchi
authors.forename: Valentina
authors.initials: V
authors.lastname: Rizzo
authors.forename: Maria Grazia
authors.initials: MG
authors.lastname: Pomponi
authors.forename: Giorgio
authors.initials: G
authors.lastname: Tasca
authors.forename: Giovanni
authors.initials: G
authors.lastname: Neri
authors.forename: Gabriella
authors.initials: G
authors.lastname: Silvestri
mesh_terms: D000328:Adult; D000368:Aged; D004252:DNA Mutational Analysis; D004576:Electromyography; D005091:Exons / Q000235:genetics; D005260:Female; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D007558:Italy; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000378:metabolism / Q000473:pathology* / Q000503:physiopathology; D009223:Myotonic Dystrophy / Q000235:genetics* / Q000473:pathology*; D065636:Myotonin-Protein Kinase; D009460:Neurologic Examination; D017346:Protein Serine-Threonine Kinases / Q000235:genetics*; D016601:RNA-Binding Proteins / Q000378:metabolism; D019680:Trinucleotide Repeat Expansion / Q000235:genetics*
chemical_list: C585517:DMPK protein, human; C493663:MBNL1 protein, human; D016601:RNA-Binding Proteins; D065636:Myotonin-Protein Kinase; D017346:Protein Serine-Threonine Kinases