Myotonic dystrophy is caused by one or more defects in the genes needed for muscle function. A defect in the dystrophia myotonica-protein kinase (DMPK) gene causes myotonic dystrophy type 1, sometimes called DM1. A defect in the CCHC-type zinc finger, nucleic acid binding protein (CNBP) gene causes myotonic dystrophy type 2, sometimes called DM2. The defects in the two genes that result in DM1 or DM2 are similar.
In both cases, a region of the genetic material called deoxyribonucleic acid (DNA) is repeated too often, so it is unstable. It forms modified messenger ribonucleic acid (mRNA), the body's set of instructions for protein formation. The modified mRNA interferes with protein production by clumping inside the cells of tissues such as muscles, so that they are unable to work properly.
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