page_title: Myotonin-protein kinase
section_title: Clinical significance
hierarchical_section_title: Myotonin-protein kinase / Clinical significance
caption_attribution_description: English: CTG repeats are located in the 3' UTR of the DMPK gene. Through formation of hairpoon loops, the repeats are contracted or expanded.
context_page_description: Myotonin-protein kinase also known as myotonic dystrophy protein kinase or dystrophia myotonica protein kinase is an enzyme that in humans is encoded by the DMPK gene.
  The dmpk gene product is a Ser/Thr protein kinase homologous to the MRCK p21-activated kinases and the Rho family of kinases. Data obtained by using antibodies that detect specific isoforms of DMPK indicate that the most abundant isoform of DMPK is an 80-kDa protein expressed almost exclusively in smooth, skeletal, and cardiac muscles. This kinase exists both as a membrane-associated and as a soluble form in human left ventricular samples. The different C termini of DMPK that arise from alternative splicing determine its localization to the endoplasmic reticulum, mitochondria, or cytosol in transfected COS-1 cells. Among the substrates for DMPK proposed by in vitro studies are phospholemman, the dihydropyridine receptor, and the myosin phosphatase targeting subunit. However, an in vivo demonstration of the phosphorylation of these substrates by DMPK remains to be established, and a link between these substrates and the clinical manifestations of myotonic dystrophy is unclear.
context_section_description: The 3' untranslated region of this gene contains 5-37 copies of a CTG trinucleotide repeat. Expansion of this unstable motif to 50-5,000 copies causes myotonic dystrophy type I, which increases in severity with increasing repeat element copy number. Repeat expansion is associated with condensation of local chromatin structure that disrupts the expression of genes in this region. As the DMPK repeat is replicated, the hairpin loop that is formed leads to repeat expansion (a) or contractions (b).
  Myotonic dystrophy (DM) 1 is an autosomal dominant neuromuscular disorder affecting approximately 1 in 8000 individuals. Affected individuals display a wide range of symptoms including myotonia, skeletal muscle weakness and wasting, cardiac conduction abnormalities, and cataracts. Despite cloning of the locus, the complex disease phenotype of DM has proven difficult to interpret, and the exact role of DMPK in the pathogenesis of DM remains unclear.
caption: CTG repeats are located in the 3' UTR of the DMPK gene. Through formation of hairpin loops, the repeats are contracted or expanded.
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