Spinal muscular atrophy (SMA) is an inherited neurodegenerative disorder characterized by progressive muscle weakness. Currently, no cure is available for SMA, but treatment options may help manage the condition. Several experimental therapies are also in development.
Spinraza (nusinersen), by Biogen, is the first disease-modifying therapy for SMA. Patients do not produce enough of a protein called survival motor neuron (SMN), due to a mutation in the SMN1 gene. Spinraza boosts the ability of a second less efficient gene, SMN2, to produce more functional SMN protein. By increasing the amount of SMN protein in the body, Spinraza can help delay motor neuron death, and slow the progression of disease symptoms.
Zolgensma, a gene therapy developed by AveXis, a Novartis company, uses a genetically engineered virus to deliver a healthy copy of the SMN1 gene to the target motor neurons to increase the levels of functional SMN protein. The U.S. Food and Drug Administration approved Zolgensma in 2019 to treat all types of SMA in patients up to age 2.
Other treatments that researchers have not specifically investigated in SMA may be beneficial to manage disease symptoms or prevent complications.
Physical and occupational therapy
Physical therapy may help maintain muscle strength and range of motion for as long as possible in patients with SMA. However, incorrect or too much exercise may cause more harm than good, so patients need to discuss exercise plans with a physical therapist before starting to exercise. A physical therapist can help tailor an exercise program for the patient, monitor progress, and change the program as necessary.
An occupational therapist can recommend specialized assistive equipment that may help some patients maintain their independence. These include braces for the arms and legs, orthotics (shoe inserts to improve walking ability), speech synthesizers, and wheelchairs.
SMA weakens the muscles in between the ribs that help the chest expand so air can enter the lungs during breathing. As a result, patients rely solely on the diaphragm for breathing, which is not very effective and causes difficulty breathing. This weakness can worsen as other muscles also deteriorate with time.
Patients may require ventilation to support breathing if they cannot get enough oxygen into their bodies. Depending on the severity of symptoms, these aids can be either non-invasive or invasive. Non-invasive ventilation is usually a short-term solution, where a mask covering the mouth delivers oxygen to the patient. Invasive ventilation involves a tube either inserted down the trachea from the mouth or surgically inserted through a small incision in the neck for long-term ventilation.
Chewing and swallowing can be difficult if the jaw and throat muscles have deteriorated. As a result, patients may struggle to get enough nutrition, which can cause weight loss and affect growth in children. Other issues may include aspiration, where food or liquid goes down the windpipe and causes lung infections.
Gastroesophageal reflux disease can also be a problem, where the muscle between the food pipe (esophagus) and stomach weakens and allows stomach acid to travel back up the food pipe.
A carefully regulated diet may be effective in managing nutritional problems. However, in more severe cases, patients may need aids such as feeding tubes. This involves a tube being passed through the nose or mouth into the stomach, or the surgical insertion of a tube through the abdomen and into the stomach. The nutrients, balanced for the needs of the patient, can then be delivered directly into the stomach via these feeding tubes.
Patients with SMA sometimes develop scoliosis where the spine becomes abnormally curved. If spotted early, a special brace for the back may be able to encourage the spine to develop correctly. However, if this does not work, surgery may be necessary to straighten the spine.
Last updated: June 16, 2020
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