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DMPK gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

DMPK gene

The DMPK gene provides instructions for a protein kinase involved in muscle, heart, and brain function, and its expansion is the primary cause of myotonic dystrophy type 1.

Normal Function

The DMPK gene provides instructions for making a protein called myotonic dystrophy protein kinase. This protein appears to play an important role in muscle, heart, and brain cells, potentially involving communication within cells and the regulation of structures inside muscle cells. For example, it has been shown to inhibit myosin phosphatase, an enzyme that plays a role in muscle tensing (contraction) and relaxation.

One region of the DMPK gene contains a segment of three DNA building blocks (nucleotides) that is repeated multiple times. This sequence, written as CTG, is called a trinucleotide repeat. In most people, the number of CTG repeats in this gene ranges from 5 to 34.

Health Conditions Related to Genetic Changes

Myotonic dystrophy

Mutations in the DMPK gene cause myotonic dystrophy type 1. This disorder is characterized by progressive muscle wasting and weakness, particularly in distal muscles such as those of the lower legs, hands, neck, and face. People with this disorder often experience myotonia, or prolonged muscle contractions, where they are unable to relax certain muscles after use.

The mutation causing this condition is a trinucleotide repeat expansion, which increases the size of the CTG segment:

  • Mild form: Usually 50 to 150 CTG repeats.
  • Classic form: Usually 100 to 1,000 CTG repeats, with symptoms beginning in adulthood.
  • Congenital form: Usually more than 1,000 CTG repeats, resulting in a more severe condition.

The mutated DMPK gene produces an altered version of messenger RNA that traps proteins to form clumps within the cell. These clumps interfere with the production of other proteins, preventing muscle cells and other tissues from functioning properly. As the gene is passed from one generation to the next, the size of the repeat expansion often increases, a phenomenon that can lead to more severe symptoms in offspring.

Frequently Asked Questions

Patients with DM1 have altered responses to anesthetic agents due to systemic smooth and skeletal muscle vulnerability and central respiratory drive defects. The use of depolarizing muscle relaxants such as succinylcholine can trigger severe, sustained generalized muscle spasms (myotonia) and life-threatening hyperkalemia. Furthermore, DM1 patients have an exquisite sensitivity to sedatives, opioids, and general anesthetics, predisposing them to prolonged post-operative respiratory depression, aspiration pneumonia, and acute cardiac conduction blocks, requiring careful preoperative pulmonary and cardiac clearance.
Cardiac conduction abnormalities occur in a majority of DM1 patients, placing them at high risk for progressive atrioventricular (AV) block, bundle branch block, ventricular tachycardia, and sudden cardiac death—often regardless of the severity of their skeletal muscle symptoms. Standard guidelines recommend a baseline 12-lead ECG and comprehensive echocardiogram at diagnosis, followed by annual ECGs and periodic 24-hour to 48-hour ambulatory Holter monitoring. Any symptoms of presyncope, syncope, or palpitation, or a PR interval extending beyond 240 milliseconds on ECG, should prompt immediate electrophysiology evaluation for possible pacemaker or implantable cardioverter-defibrillator (ICD) placement.
nticipation refers to the clinical observation that symptoms of myotonic dystrophy type 1 (DM1) become progressively more severe and appear at earlier ages in successive generations. This occurs because the CTG trinucleotide repeat expansion in the DMPK gene is structurally unstable and prone to further expansion during gametogenesis (the formation of eggs and sperm). Expansions transmitted maternally have a high risk of expanding drastically—often exceeding 1,000 repeats—which leads to the onset of severe congenital DM1 in the child of a mother who may only have had mild, late-onset symptoms.
Myotonia in DM1 is an electrical hyperexcitability of the muscle membrane (sarcolemma), not a common muscle cramp. It presents as an inability to rapidly relax muscles after a voluntary contraction, characteristically demonstrated when a patient cannot promptly release their grip after a firm handshake (grip myotonia). While common cramps can be massaged out, myotonia improves through repeated movement, known as the "warm-up phenomenon." When myotonia interferes with activities of daily living, sodium channel blockers such as mexiletine may be prescribed to stabilize the muscle membrane, provided cardiac conduction abnormalities have been ruled out.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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