A muscular dystrophy, myotonic dystrophy is a group of inherited disorders that cause muscle weakness and loss. In addition to affecting the skeletal muscles, DM also affects the heart, lungs, eyes, and endocrine system. The most common form of muscular dystrophy, DM starts in adulthood, but it can also affect children and infants.
In DM, genetic mutations affect certain proteins involved in muscle function. There are two main forms of DM, each caused by a different mutation:
A mutation in the DMPK gene on chromosome 19 causes myotonic dystrophy type 1 (DM1), also known as Steinert disease. With this mutation, a repeated sequence of DNA referred to as a trinucleotide repeat becomes abnormally expanded. In general, the more repeats, the more severe the symptoms and the earlier they begin.
DM2, also known as proximal myotonic myopathy, is caused by a mutation in the CNBP gene on chromosome 3. This mutation also involves a trinucleotide repeat expansion, but in another part of the gene.
It is inherited autosomal dominantly, which means that each child of a person with DM has a 50% chance of inheriting the mutation.
There is a wide range of symptoms associated with DM, depending on the type, the number of repeats, and the age of onset. Some of the most common symptoms are:
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.
A weakness or atrophy of the muscles can affect the arms, legs, face, neck, and trunk, causing problems with walking, balance, posture, facial expression, and breathing.
Arrhythmias, which are abnormal heart rhythms, and cardiomyopathy, which weakens the heart muscle, can cause chest pain, shortness of breath, fainting, or sudden death.
A person with respiratory problems, such as sleep apnea, in which breathing stops or becomes shallow during sleep, or respiratory failure, in which the lungs do not supply enough oxygen, can be life-threatening. Snoring, daytime sleepiness, headaches, or fatigue can be caused by these.
Cataracts, which are cloudy areas in the lens of the eye that impair vision, and ptosis, which is a drooping of the upper eyelid.
There are several types of endocrine problems, including diabetes, where the body cannot regulate blood sugar levels, or hypothyroidism, which is when the thyroid gland does not produce enough hormones. In addition to weight gain, thirst, hunger, frequent urination, or cold intolerance, they can also cause a variety of other symptoms.
Among them are intellectual disabilities, learning difficulties, attention deficit hyperactivity disorder (ADHD), autism spectrum disorders (ASD), depression, anxiety, or personality changes. Memory, reasoning, communication, social skills, and mood can be affected.
DM is diagnosed based on the clinical symptoms, family history, and genetic testing. Genetic testing is used to confirm the presence and number of trinucleotide repeat expansions in the DMPK and CNBP genes. Couples who are at risk of having a child with diabetes can also undergo genetic testing before birth (prenatal testing) or before conception (preimplantation genetic diagnosis).
As of now, there is no cure or specific treatment for DM. Treatment 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.
DM cannot be prevented, but it can be detected early through genetic testing. In order to understand their risk of having or passing on the condition, individuals with a family history of DM or carriers of the mutation can consult a genetic counselor. As well as providing information and guidance about prenatal testing and preimplantation genetic diagnosis, genetic counseling can also provide guidance on the implications.
