title: Co-segregation of DM2 with a recessive CLCN1 mutation in juvenile onset of myotonic dystrophy type 2.
abstract: Myotonic dystrophy type 2 (DM2) is a common adult onset muscular dystrophy caused by a dominantly transmitted (CCTG)(                   n                 ) expansion in intron 1 of the CNBP gene. In DM2 there is no obvious evidence for an intergenerational increase of expansion size, and no congenital cases have been confirmed. We describe the clinical and histopathological features, and provide the genetic and molecular explanation for juvenile onset of myotonia in a 14-year-old female with DM2 and her affected mother presenting with a more severe phenotype despite a later onset of symptoms. Histological and immunohistochemical findings correlated with disease severity or age at onset in both patients. Southern blot on both muscle and blood samples revealed only a small increase in the CCTG repeat number through maternal transmission. Fluorescence in situ hybridization, in combination with MBNL1 immunofluorescence on muscle sections, showed the presence of mutant mRNA and MBNL1 in nuclear foci; the fluorescence intensity and its area appeared to be similar in the two patients. Splicing analysis of the INSR, CLCN1 and MBNL1 genes in muscle tissue demonstrates that the level of aberrant splicing isoforms was lower in the daughter than in the mother. However, in the CLCN1 gene, a heterozygous mutation c.501C>G p.F167L was present in the daughter's DNA and found to be maternally inherited. Biomolecular findings did not explain the unusual young onset in the daughter. The co-segregation of DM2 with a recessive CLCN1 mutation provided the explanation for the unusual clinical findings.
authors.affiliation: Lab of Muscle Histopathology and Molecular Biology, IRCCS Policlinico San Donato, Milan, Italy.
authors.forename: Rosanna
authors.initials: R
authors.lastname: Cardani
authors.forename: Marzia
authors.initials: M
authors.lastname: Giagnacovo
authors.forename: Annalisa
authors.initials: A
authors.lastname: Botta
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Rinaldi
authors.forename: Alessandra
authors.initials: A
authors.lastname: Morgante
authors.forename: Bjarne
authors.initials: B
authors.lastname: Udd
authors.forename: Olayinka
authors.initials: O
authors.lastname: Raheem
authors.forename: Sini
authors.initials: S
authors.lastname: Penttilä
authors.forename: Tiina
authors.initials: T
authors.lastname: Suominen
authors.forename: Laura V
authors.initials: LV
authors.lastname: Renna
authors.forename: Valeria
authors.initials: V
authors.lastname: Sansone
authors.forename: Enrico
authors.initials: E
authors.lastname: Bugiardini
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Novelli
authors.forename: Giovanni
authors.initials: G
authors.lastname: Meola
mesh_terms: D000293:Adolescent; D017668:Age of Onset; D015139:Blotting, Southern; D018118:Chloride Channels / Q000235:genetics*; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D017404:In Situ Hybridization, Fluorescence; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000473:pathology; D009154:Mutation; D020967:Myotonic Disorders / Q000235:genetics* / Q000473:pathology; D009223:Myotonic Dystrophy; D016601:RNA-Binding Proteins / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: C086321:CLC-1 channel; C433227:CNBP protein, human; D018118:Chloride Channels; D016601:RNA-Binding Proteins