Spinal muscular atrophy (SMA), the leading genetic cause of death in infants and toddlers, is caused by the progressive loss of the specialized nerve cells that control voluntary movement. Age of onset, occurrence, and symptom severity vary across SMA types, particularly the main five types — 0, 1, 2, 3, and 4 — which are based on the age of symptom onset and motor milestones achieved. A younger age at SMA onset is typically associated with more severe disease.
A progressive decline in motor skills characterizes SMA. But problems with nutrition are also common, mainly due to chewing and swallowing difficulties, as well as various gastrointestinal and metabolic issues.
Poor nutrition in children with SMA can have serious consequences, as it further weakens muscles essential to breathing and the immune system. Inadequate nutrition or diet can also affect growth — with children with earlier disease onset often showing poor growth — and weight gain, as limited mobility and physical activity over time without changes in diet can raise the risk of obesity.
Patients with types 0, 1, or 2 SMA typically have difficulties sucking, swallowing, and chewing, due to weakness in the muscles of the tongue, jaw, throat, neck, and head. These difficulties are associated with a number of deficits, such as limited range of jaw movement, trouble moving food about the mouth with the tongue, a weaker bite force, and fatigue in muscles involved in chewing.
Signs of feeding problems may include prolonged mealtimes, fatigue with oral feeding, and choking or coughing when swallowing or just after swallowing. This is linked to poor coordination of the swallow with airway closure, raising the risk of aspiration, or small amounts of food or liquids entering the windpipe. Known complications of aspiration include aspiration pneumonia, lung infections, and difficulty breathing.
Feeding issues are less common in patients with SMA type 3, and rare in those with the adult-onset type 4 disease.
Gastrointestinal problems are frequent in SMA patients, such as severe gastroesophageal reflux disease (GERD) or acid reflux, delayed gastric emptying (when the stomach does not empty food as fast as it should), and constipation. Other possible symptoms of gastrointestinal distress are frequent “spitting up” or vomiting after meals, bad breath, abdominal distention (swelling), bloating, and diarrhea.
GERD, or the frequent flow of stomach acid and contents back up the windpipe (the esophagus, which carries food from the mouth to the stomach), most often affects children with type 1, a severe form of SMA. GERD it is also common in those with type 2 SMA, and less so in those with type 3. Common signs of GERD include frequent “spitting up” or vomiting after meals, complaints of chest or abdominal pain or burning sensations, bad breath, and involuntary regurgitation of food.
GERD may lead to silent aspiration, or aspiration without any warning signs, such as coughing or choking. For this reason, GERD can raise a person’s risk of pneumonia and respiratory distress.
Constipation can also frequently trouble SMA patients due to weakness in the muscles of the digestive system so that food and waste fail to move through it as they should, diets low in fiber, not drinking enough fluids, and low abdominal muscle tone. Constipation can be the cause abdominal discomfort with distention and bloating, spitting up, bad breath, or vomiting after meals.
SMA patients are particularly vulnerable to fasting states, which begin about four to five hours after finishing a meal, and to catabolism, in which the body breaks down muscles to get energy because of the fasting state. This can lead to such metabolic problems as low sugar, and unusual levels of fatty molecules in the blood. Patients may also show high blood-sugar levels, insulin resistance, problems with fatty acid metabolism, and fatty liver (a buildup of fats in the liver).
Last updated: July 23, 2021
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