Spinal muscular atrophy (SMA) is an inherited neurodegenerative disorder characterized by progressive muscle weakness. Currently, no cure for SMA exists, but there are treatments that may help manage the condition. There are also several experimental therapies in the pipeline.
Spinraza (nusinersen), by Biogen, is the first and currently only approved disease-modifying therapy for SMA. 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.
Gene therapy aims to restore the levels of functional SMN protein by delivering a functional copy of the SMN1 gene to the patient’s body.
Zolgensma, developed by AveXis, uses a genetically engineered virus to deliver a healthy copy of the SMN1 gene to the target motor neurons. The medication is currently under priority review for approval from the U.S. Food and Drug Administration. A decision is expected in May 2019.
Other treatments that have not been specifically investigated in SMA may also be used to manage disease symptoms or prevent complications.
Jaw spasms, excessive saliva production, and the inability to swallow can cause drooling in SMA patients. This may be addressed with Botox (onabotulinumtoxinA), amitriptyline, Robinul (glycopyrrolate), or AtroPen (atropine).
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, it is possible that incorrect, or too much, exercise can cause more harm than good, so it is essential to discuss exercise plans with a physical therapist before starting exercise. A physical therapist can help tailor an individualized 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 could include braces for the arms and legs, orthotics (shoe inserts to improve walking ability), speech synthesizers, or wheelchairs.
The muscles in between the ribs that help the chest expand for air to enter the lungs during breathing also weaken in SMA. This results in patients relying on the diaphragm only for breathing. However, this is not very effective and causes difficulty breathing, which can worsen as other muscles also deteriorate with time.
Patients may require ventilation to support breathing if they cannot get enough oxygen into their body. Depending on how severe symptoms are, this can be either noninvasive or invasive. Noninvasive ventilation is a short-term solution, where oxygen is delivered through a mask covering the mouth as needed. 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. This can cause weight loss and affect growth in children. Other issues may include aspiration, where food or liquid goes down the windpipe causing lung infections. Gastroesophageal reflux disease (GERD) 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, aids such as feeding tubes may be needed. 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 when the spine become severely 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 needed to straighten the spine.
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