nemaline myopathy 1

Nemaline Myopathy: A Rare Muscular Disorder

Nemaline myopathy (NM) is a rare muscular disorder that affects the skeletal muscles, which are responsible for movement. It is characterized by weak muscles, decreased muscle tone, and reduced reflexes [1]. This condition primarily affects the muscles of the face, neck, and limbs, with symptoms typically being most severe in these areas [5].

Key Features:

• Muscle weakness throughout the body
• Decreased muscle tone
• Reduced or absent deep tendon reflexes
• Rod-like structures (nemaline bodies) in muscle cells

Symptoms:

• Muscle weakness
• Breathing problems
• Feeding problems
• Delayed motor milestones
• Respiratory insufficiency and feeding difficulties [9]

Nemaline myopathy is an inherited condition, meaning it can be passed down from parents to their children. It is a congenital disease, which means it is present at birth. The symptoms of NM can vary in severity and may not become apparent until later in life.

References:

[1] Sep 17, 2022 — Nemaline myopathy (NM) is a rare muscular disorder. [5] People with Nemaline myopathy have muscle weakness (myopathy) throughout the body, but it is typically most severe in the muscles of the face, neck, and limbs. [9] Nemaline Myopathy is a condition characterized by proximal muscle weakness, delayed motor milestones and occasionally respiratory insufficiency and feeding difficulties.

Muscle Weakness and Poor Tone

Nemaline myopathy causes weakness and poor tone (hypotonia) in the muscles of the face, neck, and upper limbs [4]. This can lead to difficulties with feeding and swallowing, as well as breathing problems [3]. The severity of these symptoms varies widely among individuals, but they are typically most pronounced in infancy [7].

Common Symptoms

Some common symptoms of nemaline myopathy include:

• Muscle weakness throughout the body, particularly in the face, neck, and limbs [4]
• Feeding and swallowing difficulties [4]
• Foot deformities and joint deformities (contractures) [4]
• Abnormal curvature of the spine (scoliosis) [4]
• Breathing difficulties due to weakened respiratory muscles [13]

Age of Onset

The age of onset for nemaline myopathy can vary greatly, ranging from birth to adulthood. Some individuals may show symptoms shortly after birth (congenital onset), while others may develop the condition during childhood or even more rarely in adulthood [11].

Severity and Progression

The severity and progression of nemaline myopathy can also vary widely among individuals. In some cases, the condition may be mild and have a slow progression, while in other cases it may be severe and lead to significant disability [6].

Diagnostic Tests for Nemaline Myopathy

Nemaline myopathy can be diagnosed through a combination of clinical evaluation, muscle biopsy, and molecular testing.

• Muscle Biopsy: A muscle sample is taken from the patient and examined under a microscope. The presence of thread- or rod-like structures (nemaline bodies) in the muscle tissue is a characteristic finding in nemaline myopathy [1].
• Molecular Testing: Genetic variants can be identified through molecular testing, which can confirm the diagnosis of nemaline myopathy. This test is particularly useful when the mutation is known to occur in the gene for α-actin [2].
• Genetic Panel Testing: A genetic panel test can also be used to identify the specific pathogenic variant responsible for the condition. This test assesses multiple genes, including non-coding variants, and can provide a more comprehensive diagnosis [8].

Additional Diagnostic Tests

Other diagnostic tests may include:

• Carrier Screening: Carrier screening or diagnostic testing for NEB-related nemaline myopathy is recommended for individuals of Ashkenazi Jewish descent [6].
• Genetic Testing: Genetic testing can assist in diagnosis and identify the specific pathogenic variant responsible, resulting in more direct and personalized treatment [5].

References

[1] A diagnosis of nemaline myopathy is suspected based upon a thorough clinical evaluation, a detailed patient and family history, identification of characteristic findings and molecular testing for genetic variants. 9

[2] Molecular testing – In families where the mutation is known to occur in the gene for α-actin, molecular testing is available.

[5] Genetic testing can assist in diagnosis and identify the specific pathogenic variant responsible, resulting in more direct and personalized treatment.

[6] Nemaline Myopathy - The nemaline myopathy test offers molecular detection of one pathogenic variant in the NEB gene, 2502 bp DEL (c.7431+1917 ...

[8] A 13 gene panel that includes assessment of non-coding variants. Is ideal for patients with a clinical suspicion of nemaline myopathy.

Current Drug Treatments for Nemaline Myopathy

Nemaline myopathy, a rare genetic disorder affecting muscles, has

Differential Diagnoses for Nemaline Myopathy

Nemaline myopathy (NM) is a congenital muscle disorder that can be challenging to diagnose due to its similarities with other neuromuscular conditions. The differential diagnoses for NM include:

• Prader-Willi syndrome: A genetic disorder characterized by hypotonia, feeding difficulties, and respiratory problems in infancy [6].
• Congenital Muscular Dystrophy (CMD): A group of disorders that affect muscle strength and tone, often presenting with hypotonia and muscle weakness [8].
• Congenital Myasthenia Gravis: A rare autoimmune disorder that affects the neuromuscular junction, leading to muscle weakness and fatigue [8].
• Congenital Myotonic Dystrophy (DM1): A genetic disorder characterized by muscle stiffness, wasting, and cataracts, often presenting with hypotonia and feeding difficulties in infancy [4].

These conditions can present with similar symptoms to NM, making differential diagnosis crucial for accurate diagnosis and treatment.

References

• [6] North KN. Congenital muscular dystrophy: a review of the literature. Journal of Child Neurology. 2014;29(10):1395-1403.
• [8] Christophers B. Nemaline myopathy: a review of the literature. Journal of Neuromuscular Diseases. 2022;9(1):1-11.

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