Nemaline myopathy

A congenital neuromuscular disorder

Nemaline myopathy is a congenital myopathy characterized by muscle weakness of varying severity, typically presenting at birth or in early childhood. It is one of the most common forms of congenital myopathy and is named for the thread-like or rod-like structures, called nemaline bodies, that are found in muscle fibers when viewed under a microscope.

Presentation

Nemaline myopathy presents with a range of symptoms that can vary significantly in severity. Common features include:

• Generalized muscle weakness
• Hypotonia (reduced muscle tone)
• Delayed motor development
• Facial muscle weakness, leading to a characteristic facial appearance
• Respiratory difficulties due to weakness of the respiratory muscles
• Feeding difficulties in infants

The severity of symptoms can range from mild, where individuals lead relatively normal lives, to severe, where significant medical intervention is required.

Pathophysiology

Nemaline myopathy is caused by mutations in several genes that are important for muscle function. These genes include:

• ACTA1 - encoding skeletal muscle alpha-actin
• NEB - encoding nebulin
• TPM3 - encoding alpha-tropomyosin
• TPM2 - encoding beta-tropomyosin
• TNNT1 - encoding slow skeletal muscle troponin T

These genetic mutations lead to the formation of nemaline bodies within muscle fibers, which disrupt normal muscle function and lead to the clinical symptoms observed.

Diagnosis

Diagnosis of nemaline myopathy is based on clinical evaluation, family history, and a combination of the following tests:

• Muscle biopsy - revealing the presence of nemaline bodies
• Genetic testing - identifying mutations in the associated genes
• Electromyography (EMG) - assessing muscle electrical activity

Management

There is currently no cure for nemaline myopathy, and treatment is primarily supportive. Management strategies include:

• Physical therapy to improve muscle strength and function
• Respiratory support for individuals with breathing difficulties
• Nutritional support for those with feeding difficulties
• Orthopedic interventions for skeletal deformities

Prognosis

The prognosis for individuals with nemaline myopathy varies widely depending on the severity of the condition. Some individuals experience only mild symptoms and have a normal lifespan, while others with severe forms may have significant disability and reduced life expectancy.

Related pages

• Congenital myopathy
• Muscle biopsy
• Genetic testing