DM2 (proximal myotonic myopathy) is caused by which genetic mechanism?

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Multiple Choice

DM2 (proximal myotonic myopathy) is caused by which genetic mechanism?

Explanation:
Proximal myotonic myopathy (DM2) is caused by a CCTG repeat expansion in the CNBP gene (also known as ZNF9). This expansion produces a toxic RNA that accumulates in the nucleus and disrupts normal RNA splicing, sequestering splicing factors and leading to mis‑splicing of many transcripts. That RNA‑mediated mis-splicing underlies the myotonia and weakness seen in DM2. This mechanism is distinct from other options: a CGG repeat in FMR1 causes Fragile X syndrome, a GAA repeat in FXN causes Friedreich ataxia, and a CTG repeat in DMPK causes myotonic dystrophy type 1. In short, DM2’s disease mechanism is a CCTG repeat expansion in CNBP/ZNF9.

Proximal myotonic myopathy (DM2) is caused by a CCTG repeat expansion in the CNBP gene (also known as ZNF9). This expansion produces a toxic RNA that accumulates in the nucleus and disrupts normal RNA splicing, sequestering splicing factors and leading to mis‑splicing of many transcripts. That RNA‑mediated mis-splicing underlies the myotonia and weakness seen in DM2.

This mechanism is distinct from other options: a CGG repeat in FMR1 causes Fragile X syndrome, a GAA repeat in FXN causes Friedreich ataxia, and a CTG repeat in DMPK causes myotonic dystrophy type 1. In short, DM2’s disease mechanism is a CCTG repeat expansion in CNBP/ZNF9.

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