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?
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.
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 (SMN1) gene situated on chromosome 5. The results of this test are usually available in two to four months.
There is currently 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.
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.
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).
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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