What is nemaline myopathy?

Nemaline myopathies, or rod body myopathies, are a group of conditions which fall under the category of congenital myopathies. There are a number of different types of rod myopathies and they affect both males and females. In the majority of cases (90%) the condition becomes apparent at birth or early childhood, although in very rare cases, it does not become apparent until adulthood. Rod myopathies are estimated to affect 1 in 50,000 individuals.
 

Onset - birth to adulthood

Symptoms - weakness of muscles needed for feeding and respiration, particularly in infantile-onset disease; generalized weakness and restricted mobility; spinal curvature may occur

Progression - infantile-onset cases are most severe; difficulties with feeding and respiration resulting from lack of muscle strength and tone may lead to death; affected children attain motor milestones slowly, might weaken further at puberty

Inheritance - autosomal dominant, or produced by a defective gene contributed by one parent; also autosomal recessive, or produced by defective genes contributed by both parents

What causes it?
In the majority of cases, a rod myopathy is inherited, although there are sometimes sporadic cases where there are no other family members affected. There have been mutations identified in 5 different genes, which cause a rod myopathies. The protein products of all of these genes are involved in muscle tone and contraction.

ACTA1 - This gene produces a protein called α- actin. Mutations in this gene account for around 15-25% of cases. Errors in this gene are inherited in an autosomal dominant or autosomal recessive pattern.

NEM2 - The product of this gene is a protein called nebulin. It is thought that mutations in this gene are a common cause of nemaline myopathy but definite statistics are unavailable. Mutations in this gene are inherited in an autosomal recessive pattern.

TPM3 - The product of this gene is a protein called α- Tropomyosin 3. Mutations in this gene account for only 2-3% of affected individuals, and are inherited in an autosomal dominant or autosomal recessive pattern.

TPM2 - This gene encodes a protein called β-Tropomyosin. Only very few individuals have been identified with errors in this gene. Inheritance is in a autosomal dominant pattern.

TNNT1 - This gene produces a protein called Troponin 1. Errors in this gene have only been identified in a population of Old Order Amish individuals. Inheritance is in an autosomal recessive pattern.

Is there a treatment?
There is currently no effective treatment to halt the progression of the nemaline myopathies, but management of the condition is very important for prolonging life.

• Night time ventilation - Breathing problems are common with the nemaline myopathies, and thus respiratory function should be regularly monitored. A decrease in oxygen intake can lead to, among other things, headaches, breathlessness, poor appetite and disturbed sleep. Night time ventilation involves the use of a face mask attached to a small machine, which assists in breathing. This aids the muscles which control breathing, and allows a greater intake of oxygen. Night time ventilation may be beneficial to people with a rod body myopathy, but this should be discussed fully with a consultant to determine whether it is appropriate.
   

• Feeding tube (or gastrostomy) - This is a tube that goes into the stomach through the stomach wall and enables a person to be given food and fluids by passing them directly into the stomach via the tube. People with a myopathy may have problems with swallowing which can lead to choking and inhalation of food. This can results in chest infections. A feeding tube prevents this from happening. There are a number of different types of feeding tube which are available, and these are fitted by a short surgical procedure. A factsheet on Gastrostomy is available from the Information and Support Line.
   

• Physiotherapy - The primary aim of an individual with a neuromuscular disorder is to increase or at least maintain function and mobility. Physiotherapy can assist in doing this, and it can also maintain breathing capacity, delay the onset of curvature of the spine (scoliosis), and help prevent the development of contractures. It is important that the physiotherapist involved is familiar with the treatment of people with neuromuscular disorders.
   

• Exercise - There is debate over whether people with neuromuscular disorders should undertake strenuous physical exercise. Some say that putting additional strain on already weakened muscles will cause additional harm, whilst others believe that the exercise may increase muscle strength. Insufficient evidence exists to support either, but it is believed that moderate non-weight bearing exercise such as swimming, walking or peddling may be the best solution. This sort of aerobic exercise helps to maintain a healthy cardiovascular system and a steady weight. It is however, important that this is discussed fully with a clinician.
   

• Antibiotics - Chest infections are common with the nemaline myopathies and complications with breathing can lead to a variety of other problems, including lethargy, headaches, and poor appetite. Antibiotics are used to treat chest infections. There are a variety of antibiotics available, and a GP will be able to advise on the most suitable. If there is a tendency to chest infections it is worth considering pneumovax (prevenar in children under two years) and the flu vaccine.