The muscle and other organs of the body are affected by myotonic dystrophy type 2 (DM2). Myotonic dystrophy type 2 (DM2) is a type of muscular dystrophy that causes muscle weakness and delayed relaxation of muscles. Myotonic dystrophy type 2 (DM2) is generally milder than myotonic dystrophy type 1, but it can still cause significant problems with daily activities and quality of life.
On chromosome 3, a mutation in the CNBP gene causes DM2. This mutation results in an abnormal expansion of a tetranucleotide repeat sequence of DNA. In general, the more repeats, the more severe the symptoms and the earlier they develop. However, there is no clear correlation between the repeat size and the clinical features of DM2.
A person with DM2 has a 50% chance of passing down the mutation to each of their children because the condition is inherited as an autosomal dominant trait.
A person with DM2 usually develops symptoms between the ages of 20 and 60, and some of the most common symptoms are:
Atrophy and weakness of muscles, especially in the proximal muscles (those closer to the center of the body), such as the shoulders, hips, thighs, and upper arms. This can make it difficult to walk, climb stairs, lift objects, or perform other physical activities.
A myotonia is a delay in the ability to relax muscles after contracting them. It can affect any muscle, including the hands, eyelids, tongue, or throat and can cause stiffness, cramping, or difficulty swallowing.
Exercise, cold, stress, and fatigue can trigger muscles pain that can be severe and chronic, affecting the back, neck, arms, and legs.
Cataracts, which are cloudy areas in the eye's lens that impair vision, can develop in people with DM2 at a young age (before 50), and can affect one or both eyes.
Arrhythmias (abnormal heart rhythms) and cardiomyopathy (weakening of the heart muscle) can cause chest pain, fainting, or sudden death. DM2 has fewer heart problems and less severe heart problems than DM1, but it still needs to be monitored and treated regularly.
A respiratory condition such as sleep apnea (a condition in which breathing stops or becomes shallow during sleep) or respiratory failure (a life-threatening condition in which the lungs do not supply enough oxygen to the body) can result in snoring, daytime sleepiness, headaches, or fatigue.
Diabetes (a condition in which the body cannot regulate blood sugar levels), hypothyroidism (a condition in which the thyroid gland does not produce enough hormones), or low testosterone (a condition in which the male sex hormone is lacking) are some examples of endocrine problems. The symptoms can include weight gain, thirst, hunger, frequent urination, or cold aversion.
Problems with memory, reasoning, communication, social skills, or mood, such as mild cognitive impairment, learning difficulties, attention deficit hyperactivity disorder (ADHD), depression, anxiety, or personality changes.
Clinical symptoms, family history, and genetic testing are used to diagnose DM2. Genetic tests can confirm the presence and number of the tetranucleotide repeat expansions in the CNBP gene. For couples at risk of having a child with DM2, genetic testing can also be done before birth (prenatal testing) or before conception (preimplantation genetic diagnosis).
The treatment of DM2 aims to manage symptoms and prevent complications. The treatment may include:
Myotonia, seizures, or muscle pain can be reduced with medications such as anticonvulsants, muscle relaxants, or pain relievers.
Devices that regulate heart rhythm or prevent sudden cardiac arrest, such as pacemakers and implantable cardioverter defibrillators (ICDs).
Devices that improve breathing during sleep or respiratory failure, such as continuous positive airway pressure (CPAP) or bi-level positive airway pressure (BiPAP).
Correcting eye problems, facial weakness, or scoliosis with surgery such as cataract removal, eyelid lifts, or spinal fusions.
A physical therapist, occupational therapist, or speech therapist can help improve muscle strength, mobility, function, or communication.
Supporting weakened muscles with assistive devices, such as braces, canes, walkers, or wheelchairs.
Learning difficulties or cognitive impairments may require special education, tutoring, or accommodations.
Counseling, medication, or therapy to cope with depression, anxiety, or emotional distress.
It is not possible to prevent DM2, but it can be detected early using genetic testing. To understand their risk of having or passing on the condition, individuals with a family history of DM2 or who carry the mutation can consult a genetic counselor. As well as providing information and guidance on prenatal testing and preimplantation genetic diagnosis, genetic counseling can also provide information and guidance on options and implications.
