Myotonic Dystrophy Is Associated with a Reduced Level of RNA from the DMWD Allele Adjacent to the Expanded Repeat

Abstract

Myotonic dystrophy is caused by the expansion of a CTG repeat sequence. The mechanism by which this expanded repeat produces the pathophysiology of myotonic dystrophy is not clear. It has been shown previously that expansion of the repeat produces allele-specific effects on transcripts from two genes, DMPK and SIX5. We have examined the effect of repeat expansion on the level of RNA from a third gene, DMWD. We have identified a polymorphism in this gene and developed a quantitative allele-specific assay for DMWD RNA levels, which we have applied to nuclear and cytoplasmic fractions of RNA from DM cell lines. We have found that the level of the DM-associated allele in the cytoplasm of DM cell lines is reduced by 20-50% compared with the wild-type allele, similar to the level of reduction found for SIX5 in allele-specific analysis. However, no such reduction is observed in RNA from the nuclear fraction of DM cell lines. This may reflect the complex nature of processing transcriptional units at the DM locus.

Electrophysiological evaluation in myotonic dystrophy: correlation with CTG length expansion

“…Alteration in the function of slow potassium channels can produce myotonia 26 . Recently, evidences based on a transgenic mice, support a possible mechanism of RNA gain of function in the pathogenesis of MD 15 .…”

“…Currently explanations include: deficiency of the DM protein kinase 14 ; effect of expanded CTG repeats on neighboring genes [15][16][17][18] ; interference of the mutant DM protein kinase transcripts with others transcripts (trans RNA interference) 19 . Studies that are in progress look for new transgenic models that may more closely resemble clinical DM and that provide also a model for anticipation 20,21 .…”

DNA Methylation and Trinucleotide Repeat Expansion Diseases

“…Firstly, expression of an expanded CUG RNA sequence causes a toxic gain-of-function effect by altering the activity of RNA splicing factors (Ranum & Cooper, 2006). Secondly, the expanded CTG repeat induces epigenetic changes, including DNA methylation, at the DM1 locus that result in reduced expression of the DMPK gene and upstream and downstream genes SIX5 and DMWD (Klesert et al, 1997;Alwazzan et al, 1999;Eriksson et al, 2001). Disease-associated DNA methylation was first reported to occur within a region approximately 1kb upstream of the DMPK gene (Steinbach et al, 1998).…”

Myotonic Dystrophy Type 1 (DM1): From the Genetics to Molecular Mechanisms

“…b. A second mechanism proposed to explain the pathogenesis of DM1 is based on the effect exerted by CTG expanded repeats on chromatin structure (Otten & Tapscott, 1995), which in turn might lead to partial silencing of neighboring DMWD (Dystrophia myotonica-containing WD repeat motif) and SIX5 (Sine oculis homeobox homolog 5) genes (Alwazzan et al, 1999;Klesert et al, 1997;Sarkar et al, 2000). This hypothesis is supported by the fact that DMWD expression levels are reported as decreased in repeat expansion-bearing patients (Alwazzan et al, 1998;Gennarelli et al, 1999).…”