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Spinal Muscular Atrophy Type 0 & 1

SMA type 1 or Werdnig-Hoffman disease, the most severe type of SMA, presents before the age of 6 months. These children have severe muscle weakness and never acquire the strength to sit, crawl or walk. They may look completely normal at birth but usually after just a few months their parents notice problems with motor development, swallowing and breathing. In some cases symptoms might start while the baby is still in a womb. Some doctors classify this as type 0 SMA or prenatal onset SMA. Mothers of affected infants notice decrease or loss of fetal movement at the end of their pregnancies. When these babies are born they appear floppy and might have joint contractures.  They develop severe breathing and swallowing problems very early on (sometimes in the first few days of their lives) and have a very short life expectancy. 80% do not reach their first birthday.

The biggest threat to the lives of SMA type 1 affected children is respiratory problems. Respiratory problems arise due to chest wall muscle weakness and lung underdevelopment. These children develop what is called a "paradoxical breathing" pattern, when the work of breathing is mainly done by muscles of the abdomen and the diaphragm. This results in a bell-shaped chest appearance . [6]

Breathing muscles weakness results in weak cough, which makes it difficult for these infants to clear their own secretions and puts them at risk for pulmonary complications. Another contributing factor to breathing problems is bulbar weakness - weakness of the muscles of the lips, the tongue and the pharynx. It causes swallowing and feeding difficulties and greatly increases the risk of aspiration pneumonia - pneumonia caused by aspirating food, formula or breast milk into the lungs. [6]

Hypoventilaton at night - not taking deep enough breaths and failing to maintain adequate oxygenation is another problem caused by weakening muscles of the chest.

Respiratory complications and failure is the leading cause of death in SMA types 1 and 2. Without respiratory support majority of children with type 1 SMA die before they turn 2 years old. [7]

SMA also causes gastrointestinal and nutritional problems. Common complications include constipation, delayed gastric emptying, gastroesophageal reflex and growth failure. [8] Because of difficulties with chewing and swallowing, these patients often require placement of feeding tubes to improve nutrition and minimize risk of aspiration.

SMA type 1 patients also suffer from orthopedic complications. Progressive weakness and immobility cause tightness of the joints (contractures). These may be prevented by doing range of motion exercises and physical therapy. Pain medicine is used to control discomfort associated with orthopedic complications.

6. Robert T. Leshner, MD, Professor. Spinal Muscular Atrophy Type 1. Retrieved from
7.Spinal Muscular Atrophy Pulmonary Care. Overview of Pulmonary Problems in Spinal Muscular
Atrophy. From Consensus Statement for Standard of Care in Spinal Muscular
Atrophy. Retrieved from
8. Spinal Muscular Atrophy GI and Nutrition Care. Overview of Gastrointestinal and Nutritional Complications in Spinal Muscular Atrophy. From Consensus Statement for Standard of Care in Spinal Muscular  Atrophy. Retrieved from
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