Overview

Myotonic dystrophy is a rare progressive disorder that is characterised by muscle weakness, with two different forms: DM1 and DM2.¹ The gene that codes for DM protein kinase, DMPK, has a CTG repeat that has expanded in its 3’ non-coding region, causing DM1.² 

On the other hand, myotonic dystrophy type 2 (DM2), another form of the illness, is caused by a repeat expansion in a separate gene. Zinc Finger 9 (ZNF9) has a CCTG repeat in its first intron, involved in DM2 expansion. DM1 and DM2 are inherited in an autosomal dominant manner, meaning that only one parent needs to possess an altered gene for it to be passed on.² They are hereditary illnesses that impact the brain, heart, eyes, smooth and skeletal muscle, and other organs.³ Activities of everyday life that require a high level of muscular strength, stability, and coordination are difficult for people with this illness to do. Despite this, most patients can still carry out necessary daily tasks independently, even as the condition progresses.⁴ 

Symptoms of myotonic dystrophy

The hallmark symptoms of myotonic dystrophy are muscle weakness, atrophy (wasting), and myotonia (being unable to relax muscles on desire). In (DM1), symptoms often manifest in adulthood, with the primary symptom being myotonia. Patients may also experience distal muscular weakness, creating issues with fine motor activities with hands and a foot drop that impairs an individual’s ability to walk. Similarly, the symptoms of DM2 can vary and usually start in adulthood. Some symptoms include loss of hearing and weakness of proximal muscles.⁵ 

Diagnosis and tests of myotonic dystrophy

A physical examination is typically performed to determine whether an individual has myotonic dystrophy. The individual is asked about their symptoms and medical family history, especially history related to myotonic dystrophy since this is a hereditary condition.⁵ 

Diagnosis of myotonic dystrophy can be determined by genetic testing. Genetic testing confirms the diagnosis, identifying mutations in the DMPK gene for DM1 and the CNBP gene for DM2. However, before proposing genetic testing, medical professionals may perform other tests if they are uncertain about a patient having myotonic dystrophy, including the creatine blood test. When the heart or skeletal muscles are damaged, creatine kinase enzyme is secreted in the blood. Another test that may be used is the electromyogram (EMG), which involves measuring the electrical activity of muscle fibres. Lastly, a muscle biopsy can be done, where samples of cells are taken from a muscle. These are examined under a microscope to investigate the signs of myotonic dystrophy.⁵    

Management and treatment of myotonic dystrophy

There is currently no cure for myotonic dystrophy, but treatment focuses on controlling symptoms and increasing independence and standard of living. A myotonic dystrophy patient’s body can be impacted in several areas; therefore, treatment options may vary based on symptoms. Some treatment options include medications that lessen chronic myotonia such as sodium channel blockers, a CPAP machine for patients suffering from sleep apnea, and neurostimulants for patients experiencing severe drowsiness during the day.⁵ 

Some patients may experience dysphagia, involving difficulties in swallowing. In mild cases of dysphagia, speech therapy and nutrition might occasionally assist with mild dysphagia. However, aspiration pneumonia is a potential outcome of severe dysphagia, which can be avoided by a different feeding style. In such cases, a gastrostomy may be necessary. This entails a simple surgery to insert a tube straight into the stomach via the front of the abdomen.⁶

Daily life challenges 

Patients with myotonic dystrophy face a range of challenges beyond muscle weakness. The disease can impair eyesight, alter hormone levels, and cause gastrointestinal problems, personality disorders, decreased cognitive function, and respiratory problems. Initially, facial, eyelid, jaw, and neck muscles are impacted. Further, the forearm muscles that allow us to hold items are frequently impacted from a young age and patients often also experience foot drop due to the weakening of the muscles surrounding the ankles, which can lead to tripping and toe catching. In the long run, some patients may require a wheelchair if muscle deterioration is more severe than others. Furthermore, patients suffering from myotonia will have trouble relaxing their muscles, reducing the overall quality of life of myotonic dystrophy patients.⁷ 

Frequent disruptions occur to a patient’s heart wiring, causing periods of dizziness or even cardiac arrest. Consequently, some patients may be advised to get a pacemaker or another device to manage these symptoms. In addition, in some patients, there may be an impact on ventilation or air moving into and out of the lungs.⁷ This could make patients drowsy during the day and raise the chances of getting a chest infection. 

When eating or drinking, swallowing can frequently result in coughing since the swallowing muscles are impacted. Food or liquids that enter the lungs instead of the stomach can cause aspiration pneumonia, a serious chest infection. Furthermore, similar symptoms of irritable bowel syndrome are commonly seen in the lower intestines, presenting as a combination of diarrhoea, cramping abdominal discomfort, and constipation.⁷ 

Future directions and research

As of now, myotonic dystrophy does not have a cure. The pathophysiology of myotonic dystrophy has been investigated, revealing a novel disease pathway that requires new treatment approaches. Myotonic dystrophy is an RNA-mediated illness. An expanded repeat RNA produced by the mutant gene's expression is toxic to cells. The malfunction of two types of RNA binding proteins is an effect of RNA toxicity in myotonic dystrophy, and it results in improper control of alternative splicing of certain genes.⁸ 

Therapy aimed at directly targeting the RNA illness mechanism will soon replace the current treatment as our understanding of pathophysiology improves. Early clinical studies are currently testing novel pharmaceutical strategies in treating myotonia and muscle atrophy in DM1, and preclinical models have demonstrated the potential of treatments intended to undo RNA damage. Ribonuclear inclusions may be instrumental l therapeutic targets to find novel substances that alter the toxicity of RNA. Testing new therapeutic approaches when they become available will be made possible by the ongoing creation of suitable model systems.⁸

Summary

Myotonic dystrophy profoundly impacts patients’ quality of life, particularly through its effects on the heart and lungs. Despite this, various interventions can be done to manage this illness. There is unfortunately no cure for myotonic dystrophy, but medical professionals can recommend various management strategies for different symptoms including dysphagia and sleep apnea. Since researchers and scientists are now aware of the main biological causes of myotonic dystrophy, targeted treatment is now being explored to improve patient outcomes.