Spinal muscle atrophy (SMA) is a genetic disease characterized by the progressive loss of motor neurons — the nerve cells that control muscle movement. This leads to muscle weakness and atrophy.

There are several types of SMA, based on when symptoms appear, their severity, and which gene is affected. SMA types 0 to 4 are all caused by mutations in the SMN1 gene that provides the instructions to make a protein called SMN. This protein is essential for the survival of motor neuron. It is thought that the severity of the disease is determined at least to some extent by the number of copies of a second gene called SMN2 from which some SMN protein can be made.

What is SMA type 1?

SMA type 1, also called Werdnig-Hoffman disease, is the most common type of SMA. Patients with this type of SMA exhibit symptoms at birth or by the age of six months.

Symptoms

Infants with SMA type 1 generally have symptoms that include hypotonia (weak muscle tone, especially in the arms and legs), and difficulty moving, eating, breathing, and swallowing. Infants are unable to raise their head or sit unaided. Cognition is not affected by the disease and infants with SMA type 1 are generally bright, responsive, and alert.

Diagnosis

Tests such as an electromyography or a muscle biopsy may be used to diagnose SMA.

The most certain way of diagnosing the disease is DNA testing. A small blood sample is taken and used to look for mutations in the survival motor neuron 1 (SMN1gene situated on chromosome 5.  The results of this test are usually available in two to four months.

Treatment

Currently, there is no cure for SMA. However, there are treatments available to help manage symptoms, reduce discomfort, and maintain quality of life for as long as possible.

Spinraza (nusinersen) is a groundbreaking, disease-modifying treatment developed by Biogen for spinal muscular atrophy (SMA). It became the first therapy ever approved by the U.S. Food and Drug Administration (FDA) to treat SMA in both infants and adults in December 2016, under a priority review program for rare diseases, after it showed statistically significant improvements in both motor function and survival. Spinraza also received approval to treat infantile-onset SMA, as well as SMA types 1, 2 and 3.

Other cutting-edge treatments which may substantially improve quality of life and survival are on the horizon. Zolgensma, previously knowns as AVXS-101, is the proprietary gene therapy candidate in the late stages of development by AveXis that is designed to treat SMA type 1 in infants. Zolgensma is a gene therapy designed to deliver a functional copy of the SMN1 gene to motor neurons in SMA patients.


Watch an informational video about the importance of newborn screening in diagnosing SMA and other genetic diseases as early as possible.


Caring for an infant with SMA type 1 requires meeting with a multidisciplinary health care team to ensure that the infant is receiving the appropriate care.

Parents should meet with a physiotherapist or an occupational therapist to discuss options for helping their baby sleep comfortably. Therapists may also be able to prescribe a wedge to prop up the baby so the child can breathe more easily.

Frequent respiratory checkups are very important to ensure that the baby’s airways remain clear even when the child has difficulty swallowing. Patients are also more susceptible to respiratory infection. As the disease progresses, patients may need respiratory interventions, which may include a suction device to clear airways, or a ventilator to support lung function.

Glycopyrrolate or other medications may be prescribed to reduce drooling. These medications must be prescribed carefully, as they may make secretions thicker and more difficult to expel.

For infants who have trouble eating enough to maintain body weight, other methods of feeding may be necessary. These include a nasogastric tube (a feeding tube inserted through the nose to the stomach), a nasojejunal tube (a feeding tube inserted through the nose past the stomach into the small intestine), or a gastrostomy tube (a feeding tube that is surgically inserted into the stomach through the abdomen).

Constipation is a common problem for infants with SMA, and some patients may have acid reflux. Treatment for these symptoms should be discussed with the healthcare team to find the best option. 

Outlook

The initial symptoms of muscle weakness become more severe as the disease progresses. Most infants with SMA type 1 do not survive past age 2, usually because of respiratory failure.

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SMA News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.