Nemaline myopathy is a genetically acquired disease that causes muscle weakness to varying degrees. It is a relatively rare disease with an estimated onset of 1 out of 50,000 individuals. It is a type of muscular dystrophy. When a biopsy is taken from muscle tissue, abnormal thread like rods called nemaline bodies can be seen. Figure one visually demonstrates this phenomenon.
There are at least six types of mutations that are recognized in the disease. The most commonly seen mutations arise in the NEB and ACTA1 gene sets. When NEB gene mutations are seen, the effects of the disease are typically seen in childhood. When mutations are seen in ACTA1, the disease’s severity and age of onset can vary greatly.
Genetics and Inheritance
The inheritance of the genetic disease proceeds by an autosomal recessive mechanism. This means that the parents of an affected individual will each carry one copy of the disease genetics but themselves will not have the disease.
The genetic mutations in patients suffering from nemaline myopathy manifest themselves in disorganized microfibers of the muscle tissue. Nemaline refers to threads, and myopathy refers to pathology of muscle. Specifically the protein a-actin is genetically distorted. These mutations interfere with the skeletal muscle fibers’ ability to form proper contractions.
The patient suffers to varying degrees with the most severe cases manifesting at birth. The disease is divided into six sets depending on the severity. These sets, listed from most severe to least severe, are called Severe congenital, Amish, intermediate congenital, typical congenital, childhood-onset, and adult-onset.
The severe congenital and Amish varieties are typically fatal at an early age. The most common form of the disease is the typical congenital type. Most people that have the typical congenital type can walk without assistance and don’t have severe breathing difficulties.
Manifestations and Treatments of the Disease
Typical problems arise mainly in respiratory, bulbar, and trunk muscles. Scoliosis may develop as well as joint irregularities. As patients grow, a slender appearance may be seen due to the effect of muscle weakness. Physiotherapy is recommended to help with physical development issues. Pneumonia and chest infections can be real concerns due to lessened respiratory function. Reflux can also be an issue due to muscle immobility associated with the disease. It is recommended to treat respiratory infections quickly and thoroughly.
Development of children with the disease can limit mobility. Particularly, children may have a delay in walking compared to their peers and may need a wheelchair or orthopedic interventions.
It is critical to monitor respiratory function, as respiratory muscles may be affected with this disease. Ventilation via tracheostomy may be necessary in severe cases. Mechanical devices may be necessary to assist breathing, especially at night.
Since bulbar muscles may be affected by the disease, there may be impediments with normal functioning of the throat. Patients with severe cases are unable to swallow and may need to receive nutrition through feeding tubes. Communication may also be adversely effected by the bulbar muscle weakness. Speech therapy in conjunction with medical speech devices may help to improve speech impediments.
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