DMPK, a member of the Ser/Thr protein kinase family, may play a role in intracellular communication. Most DMPK isoforms are expressed in many tissues including heart, skeletal muscle, liver and brain, except for isoform 2 which is only found in the heart and skeletal muscle, and isoform 14 which is only found in the brain, with high levels in the striatum, cerebellar cortex and pons. The poly-Gln region upstream/downstream of the gene is highly polymorphic (5 to 27 repeats) in the normal population and is expanded up to 50-3000 or more repeats in DM patients. The repeat length usually increases in successive generations, but not always. Defects in DMPK are the cause of myotonic dystrophy (DM), also known as Steinert disease. DM is an autosomal dominant neurodegenerative disorder characterized by myotonia, muscle wasting in the distal extremities, cataract, hypogonadism, defective endocrine functions, male baldness, and cardiac arrhythmias. DM patients show decreased levels of kinase expression inversely related to repeat length. The minimum estimated incidence is 1 in 8000 live births.
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