Introduction
Generally, myotonic dystrophy is a multistage disease that typically presents as muscle weakness, myotonia (muscular wasting), cardiac conduction abnormalities, and cataracts. The prevalence of myotonic dystrophy could significantly vary among ethnic and geographic regions. However, the incidence rate is about one in 80,000 people globally. Moreover, myotonic dystrophy is considered the most common muscular dystrophy among European ancestors.
What Is Congenital Myotonic Dystrophy?
Myotonic dystrophy is a form of muscular dystrophy, whereas muscular dystrophy refers to a genetic group of rare neuromuscular conditions that result in progressive frailty and breakdown of muscles over time. Skeletal muscles are primarily affected by myotonic dystrophy, with less and rare cardiac muscle involvement. In this condition, the muscles have difficulty attaining relaxation after contraction. The other significant manifestations of muscular dystrophy include intellectual disabilities (a neurodevelopmental condition characterized by impaired intellectual functioning) and cataracts (cloudiness of an area in the lens resulting in vision impairment). Myotonic dystrophy is known to occur at any age. Nevertheless, the onset of this condition is more common between 20 and 30 years of age. Myotonic dystrophy presents a wide range of signs and symptoms. It could affect various organs and their respective body systems, including the eyes, skeletal muscles, cardiac muscles, cardiovascular, central nervous, and endocrine systems.
What Causes Congenital Myotonic Dystrophy?
Myotonic dystrophy is congenital (present from birth) or inherited (passed from parent to offspring). Mutations or structural changes in the genes DMPK and CNBP cause type 1 and type 2 of myotonic dystrophy, respectively. In each condition, a specific segment of the deoxyribonucleic acid (DNA) is abnormally formed and repeated several times, leading to the formation of an unstable layer in the gene. The greater the frequency of abnormal repetition of DNA, the greater and more serious the symptoms accompanying the myotonic dystrophy condition will be. Certain clinical research studies signify that the excess messenger that ribonucleic acid (RNA) generated from the abnormal repetition of DNA can be toxic, influencing the production and regulation of many proteins in the cells. This eventually induces severe signs and symptoms in many organs, including the heart, in myotonic dystrophy condition.
What Is the Pathophysiology of Congenital Myotonic Dystrophy?
Congenital myotonic dystrophy (CMD) is typically associated with an expanded CTG repeat in the DMPK gene, leading to abnormal production of the dystrophia myotonica protein kinase (DMPK) messenger RNA. This expanded repeat can be transmitted from an affected mother, and the severity of CMD can vary. In CMD, symptoms are present at birth or shortly thereafter, and affected infants may display muscle weakness, respiratory difficulties, and developmental delays. Pathologically, CMD involves multisystemic manifestations. Microscopically, muscle biopsies often reveal myopathic changes, including fiber atrophy, degeneration, and the presence of ring fibers. These structural alterations contribute to the muscle weakness observed in individuals with CMD. Additionally, cardiac involvement is common in CMD, and histological examination of the heart may reveal fibrosis, myocyte disarray, and other abnormalities, leading to cardiomyopathy and potential cardiac conduction defects. The neurological and systemic impact of CMD arises from the underlying genetic mutation and its effects on cellular functions, accentuating the importance of understanding molecular pathology for comprehensive management and potential therapeutic interventions.
What Are the Signs and Symptoms of Congenital Myotonic Dystrophy?
Myotonic dystrophy has several types, including a range of corresponding symptoms. The signs of congenital myotonic dystrophy before birth are as follows.
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Polyhydramnios (excess amniotic fluid around the fetus during pregnancy)
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Clubfoot (conditions where the fetus's foot is twisted or out of position).
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Ventriculomegaly (enlarged ventricles in the brain because of the accumulation of cerebrospinal fluid).
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Decreased fetal movement in the uterus.
The symptoms associated with congenital myotonic dystrophy in growing children and adults include:
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Slurred speech or dysarthria.
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Intellectual disability.
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Hypotonia (decreased muscle tone).
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Pointed or prominent appearance of the lip resulting from weakened facial muscles.
What Are the Cardiac Manifestations of Congenital Myotonic Dystrophy?
Congenital myotonic dystrophy is known to affect the skeletal muscle, primarily. However, it can also have the involvement of cardiac muscles, resulting in certain heart-related problems. The cardiac manifestations showing cardiac muscle involvement in congenital myotonic dystrophy include the following.
Conduction Abnormalities:
The heart’s conduction system comprises a network of signals that keep the heart functioning. The electrical signals of the conduction system make the heart contract and relax. Each contraction is also responsible for controlling and regulating blood flow through the heart. Conditional disorder, sometimes referred to as heart block, occurs when there is a problem with the electrical system controlling the rhythm and rate of the heart. Congenital myotonic dystrophy can sometimes affect the cardiac muscles, affecting the electrical conduction system. When a block in any branch of the heart supplies blood, the electrical signals take different forms through a ventricle. This detour signifies that one ventricle undergoes contraction for a fraction of a second layer than the other ventricles, causing arrhythmias.
Arrhythmias:
Arrhythmias are sequelae of heart conduction abnormalities. Arrhythmia refers to an irregular heartbeat, where the heart may beat too quickly (tachycardia), too slowly (bradycardia), or with an irregular pattern. In myotonic dystrophy, individuals may experience arrhythmias as part of the cardiac involvement associated with the condition. The abnormal genetic factors involved in myotonic dystrophy can affect the heart’s electrical conduction system, disrupting the normal rhythm. Common arrhythmias in this context include atrial fibrillation and heart block. Arrhythmias can contribute to symptoms such as palpitations and dizziness, and dizziness cases may lead to more serious complications.
Cardiomyopathy:
Cardiomyopathy is a congenital condition of the heart muscle that impacts the pumping ability of the heart. Cardiomyopathy can result in complete heart failure. Cardiomyopathy can accompany congenital myotonic dystrophy in many cases. The symptoms of cardiomyopathy include fatigue, dizziness, loss of appetite, rapid heart rate, shortness of breath, heart murmur, abnormal heart rhythm, and abdominal bloating. Therefore, Cardiomyopathy, a condition characterized by the deterioration of the heart muscle, is one of the potential complications associated with myotonic dystrophy. The abnormal expansion of repeated DNA sequences in the genetic code, a hallmark of myotonic dystrophy, can affect the heart muscle, causing it to weaken and function less efficiently.
Conclusion
Congenital myotonic dystrophy can impact various organs and organ systems, including cardiovascular health. The weakened cardiac muscles can result in several complications, such as conduction defects, arrhythmias, and the potential progression to heart failure. Timely and extensive cardiac monitoring, along with relevant medical interventions, are crucial for mitigating and managing the cardiac manifestations associated with congenital myotonic dystrophy. A multidisciplinary approach involving a neurologist and cardiologist provides comprehensive care for individuals with congenital dystrophy and cardiac involvement, ensuring appropriate attention and care.
