obsolete congenital muscular dystrophy merosin-positive

Merosin-positive Congenital Muscular Dystrophy: An Obsolete Form

Merosin-positive congenital muscular dystrophy (CMD) is an outdated term that was once used to describe a form of CMD characterized by the presence of merosin, a protein component of laminin. However, with advancements in medical knowledge and classification systems, this term has become obsolete.

Historical Context

In the past, CMDs were classified based on the presence or absence of merosin. Merosin-positive CMD was considered to be a distinct entity from merosin-deficient CMD. However, as research progressed, it became clear that the clinical features and genetic basis of these conditions overlapped more than initially thought.

Current Understanding

Today, CMDs are classified based on their underlying genetic causes rather than the presence or absence of specific proteins like merosin. The LAMA2 gene, which codes for laminin alpha-2 (merosin), is associated with a form of CMD known as MDC1A or primary LAMA2-CMD.

Key Features

While the term "merosin-positive congenital muscular dystrophy" may seem relevant, it's essential to note that this classification system has been largely replaced by more accurate and nuanced categorizations. The clinical features associated with merosin-positive CMD, such as muscle weakness, hypotonia, and joint contractures, are still relevant today but are now understood in the context of broader CMD classifications.

References

• [4] Primary LAMA2-CMD (MDC1A) is an autosomal recessive form of muscular dystrophy due to mutations in the laminin alpha-2 (LAMA2) gene and shows a clinical onset ...
• [7] Common features include hypotonia; progressive muscle weakness and degeneration (atrophy); joint contractures; and delayed motor milestones (i.e. sitting up, ...
• [9] Oct 22, 2024 — The clinical features of merosin-positive congenital muscular dystrophy (CMD) and merosin-deficient CMD are well known, with those of ...

Early Signs and Symptoms

The early signs and symptoms of obsolete congenital muscular dystrophy (CMD) due to merosin deficiency can be quite subtle, but they are crucial for early diagnosis. According to various medical sources [1][4][5], the following symptoms may be observed in infants with MDC1A:

• Poor or delayed head control: This is often the most common presenting sign, indicating a problem with muscle tone and coordination.
• Hypotonia (floppiness): Infants with MDC1A may have decreased muscle tone, making it difficult for them to hold their head up or maintain proper posture.
• Poor suck and cry: Some infants may experience difficulties with sucking and crying, which can be indicative of a problem with the muscles used in these actions.

Progressive Symptoms

As the condition progresses, more pronounced symptoms become apparent. These include:

• Muscle weakness and degeneration (atrophy): Over time, muscle strength and mass decrease, leading to progressive weakness.
• Joint contractures: The joints may become stiff and contracted due to muscle weakness and atrophy.
• Delayed motor milestones: Infants with MDC1A may experience delays in achieving typical developmental milestones, such as sitting up or crawling.

Other Symptoms

In some cases, additional symptoms may be observed, including:

• Respiratory failure: In severe cases, infants with MDC1A may experience respiratory difficulties due to muscle weakness.
• Failure to thrive: Infants with MDC1A may have difficulty gaining weight and growing at a normal rate.

It is essential for parents or caregivers to seek medical attention if they notice any of these symptoms in an infant. Early diagnosis and intervention can significantly improve outcomes for individuals with congenital muscular dystrophy due to merosin deficiency.

Diagnostic Features of Congenital Muscular Dystrophy (CMD) Merosin-Positive

Congenital muscular dystrophy (CMD) is a group of neuromuscular disorders that manifest at birth or infancy, characterized by hypotonia, muscle wasting, and progressive muscle weakness. The diagnosis of CMD merosin-positive involves assessing the clinical presentation, measuring elevated levels of creatine kinase, conducting brain magnetic resonance imaging, and performing biopsy examinations.

Diagnostic Tests:

• Clinical Presentation: The initial symptoms are present at birth or in the first few months, including hypotonia, muscle wasting, and progressive muscle weakness.
• Elevated Creatine Kinase Levels: Measuring elevated levels of creatine kinase can help confirm the diagnosis of CMD merosin-positive.
• Brain Magnetic Resonance Imaging (MRI): Conducting brain MRI can help identify any structural abnormalities in the brain that may be associated with CMD merosin-positive.
• Biopsy Examinations: Biopsy examinations, including muscle biopsy and histopathological examination, are essential for confirming the diagnosis of CMD merosin-positive. A finding of reduced merosin in muscle is predictive of severe weakness and disability.

Diagnostic Features:

• Reduced merosin levels in muscle tissue
• Elevated creatine kinase levels
• Hypotonia and muscle wasting at birth or infancy
• Progressive muscle weakness

These diagnostic features can help confirm the diagnosis of CMD merosin-positive, which is a prevalent cause of congenital muscular dystrophy. However, it's essential to note that the diagnosis of CMD merosin-positive involves assessing the clinical presentation, measuring elevated levels of creatine kinase, conducting brain MRI, and performing biopsy examinations.

References:

• [8] Congenital muscular dystrophy (CMD) is a group of neuromuscular disorders that manifest at birth or infancy, characterized by hypotonia, muscle wasting, ...
• [11] Congenital muscular dystrophy (CMD) resulting from merosin or laminin alpha-2 deficiency is a prevalent cause of CMD.
• [13] Biopsies showing few acid phosphatase-positive cells in association with numerous alkaline phosphatase staining muscle fibers are specific for congenital muscular dystrophy syndromes and histopathological support for the diagnosis.

Treatment Options for Merosin-Positive Congenital Muscular Dystrophy

While there is no specific treatment available for congenital muscular dystrophies (CMDs), including the merosin-positive type, aggressive supportive care is essential to preserve muscle function and overall health.

• Corticosteroid therapy: Corticosteroid drugs like prednisone have been given to patients with some types of CMD on occasion [3]. However, it's essential to note that this treatment approach may not be effective for all individuals.
• Protein substitution therapy: Research has shown that laminin-111 can serve as an effective protein substitution therapy for the treatment of muscular dystrophy in animal models [5].
• Physiotherapy and supportive care: Treatment approaches for merosin-deficient CMD, which is a related condition, include physiotherapy to maintain muscle function and overall health. This approach may also be beneficial for individuals with merosin-positive CMD.

It's essential to consult with a pediatric neuromuscular specialist for personalized guidance on promoting optimal health maintenance and managing symptoms [4].

Differential Diagnosis of Merosin-Positive Congenital Muscular Dystrophy

Merosin-positive congenital muscular dystrophy (CMD) is a rare genetic disorder characterized by muscle weakness and degeneration. The differential diagnosis for this condition involves ruling out other possible causes of muscle weakness, particularly in children.

Other Congenital Muscular Dystrophies

• Other CMDs, such as merosin-deficient CMD, should be considered in the differential diagnosis [1].
• These conditions share similar clinical features with merosin-positive CMD, making accurate diagnosis crucial [2].

Congenital Myopathies and Myasthenic Syndromes

• Congenital myopathies, such as nemaline myopathy, can present with muscle weakness and hypotonia, similar to merosin-positive CMD [3].
• Congenital myasthenic syndromes, caused by mutations in genes encoding for acetylcholine receptors or other components of the neuromuscular junction, should also be considered in the differential diagnosis [4].

Diagnostic Workup

• A comprehensive diagnostic workup is essential to rule out these conditions and confirm the diagnosis of merosin-positive CMD.
• This may involve muscle biopsy, EMG/NCV studies, and genetic testing to identify mutations in the laminin alpha-2 gene [5].

References:

[1] Congenital muscular dystrophies (CMDs) are early onset disorders of muscle with histological features suggesting a dystrophic process. [2] The diagnosis of merosin-deficient CMD is confirmed by detecting a recessive mutation(s) (homozygous or compound heterozygous state) in the laminin alpha-2 gene. [5]