Spinal muscular atrophy (SMA) is an autosomal recessive genetic disorder which is caused by mutations in the SMN gene located on chromosome 5 (5q11.2–q13.3). In children with Spinal muscular atrophy (SMA) the neurons in the anterior horn cells of the spinal cord degenerate leading to profound muscle weakness.
Spinal muscular atrophy (SMA) is a heterogeneous group of condition and classified into SMA 1, SMA 2 and SMA 3 based of age of onset and maximum motor function which has been achieved by the child. Children with Type 1 SMA develop muscle weakness within first 6 months of life, and these infants do not achieve the ability to sit. Children with SMA Type 2 develop muscle weakness between 6-18 months of age, and these children can sit but not walk independently. SMA Type 3 has later onset, and children achieve the ability to walk independently.
Why do children with Spinal muscular atrophy (SMA) develop breathing problems?
Breathing in (inspiration) and breathing out (expiration) requires the use of several muscles such as those around the chest, in the neck and the diaphragm. In children with Spinal muscular atrophy (SMA) muscles of breathing get affected especially the intercostal muscles. The involvement of the respiratory muscles depends on the type of Spinal muscular atrophy (SMA). Children with Spinal muscular atrophy (SMA) 1 get respiratory muscle weakness early in infancy, while children with Spinal muscular atrophy (SMA) 2 get respiratory muscle weakness much later in life. Patients of Spinal muscular atrophy (SMA) 3 usually do not get much weakness of the respiratory muscles except during respiratory infections.
The weakness of the respiratory muscles in Spinal muscular atrophy (SMA) may lead to difficulties in coughing and clearing lung secretions. This in turn leads to recurrent chest infections. Weakness of the chest muscles also lead to shallow breathing called as hypoventilation leading to low oxygen and a carbon dioxide buildup in the body.
Why do children with Spinal muscular atrophy (SMA) develop breathing problems during sleep?
Children with neuromuscular disorders including Spinal muscular atrophy (SMA) first develop respiratory problems during sleep. During sleep the muscles of our body relaxes and becomes more floppy. Also when we lie down to sleep the abdominal contents push up against the diaphragm making it harder for children to breathe. As the respiratory problems worsen the child develop respiratory problems during the day as well. It is hence important to timely identify, diagnose and treat respiratory problems during sleep.
What sleep related respiratory problems are seen in children with Spinal muscular atrophy (SMA)?
Children with Spinal muscular atrophy (SMA) may have partial or complete stoppage of breathing many times in the night. Pause in breathing can last few seconds to a as long as a minute or even longer. This leads to a poor oxygen supply to the child’s brain and accumulation of carbon dioxide in the body. The brain then signals the body to wake up and the child makes an effort to start breathing again leading to gasping or snorting. As the child doesn’t get a good sleep, they are tired the next day and feel sleepy. This condition is called sleep apnea. In addition the children with Spinal muscular atrophy (SMA) also have shallow breathing called as hypoventilation.
How do we diagnose breathing problems during sleep in children with Spinal muscular atrophy (SMA)?
Children with Spinal muscular atrophy (SMA) require a sleep study or a polysomnography for proper diagnosis of sleep apnea and hypoventilation. Sleep study or a polysomnography also helps to grade the severity of the problem and hence decide treatment.
What treatment is required for children with Spinal muscular atrophy (SMA) who have sleep apnea?
Children with Spinal muscular atrophy (SMA) having sleep apnea require support with breathing at night. This is done with a small machine called as BiPap with a mask attached to the child’s nose/mouth. Bipap makes the breathing very comfortable, maintains the oxygen and carbon dioxide levels.
If your child is having Spinal muscular atrophy (SMA) do get in touch with a pediatric pulmonologist for proper respiratory evaluation and long term follow up.