Spinal Muscular Atrophy (SMA) Type 1
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Spinal Muscular Atrophy Type I, also known as Infantile Spinal Muscular Atrophy was initially described by Drs. Werdnig and Hoffman. Many texts still refer to this as Werdnig-Hoffman Disease. This is the most severe form of SMA. Some children are affected even before birth and mothers may note that during the last three months of pregnancy that fetal movements are weak. Virtually all children with Type I SMA show symptoms of weakness before age eight months. The disease tends to affect the muscles of chewing and swallowing, the chest wall muscles, and the muscles of the arms and legs. As a result, children may experience great difficulties with feeding and may even breathe milk or formula into their lungs. This places these youngsters at high risk of respiratory infections and pneumonia.
*Spinal Muscular Atrophy Type I is the Most Lethal Form of SMA
The weakness of the chest wall muscles (intercostal and accessory respiratory muscles) makes it difficult for these youngsters to breathe deeply or to generate a strong cough. Some of the breathing muscles, especially the diaphragm, are relatively unaffected. This may produce an unusual shape of the chest with a sunken appearance and a bell-like configuration of the chest wall. Each inspiration seems to be generated from the abdomen and "belly breathing" is often noted by parents and physicians.
Weakness in the arms and legs makes it difficult for the children to roll over and children with Type I SMA are never able to sit without assistance.
Weakness of the neck muscles makes it difficult for these children to achieve head control. Quivering of the tongue is often noticed. This has been termed tongue fasciculation. This clinical sign is seen in virtually no other disease in children except for spinal muscular atrophy.
Children with Type I SMA face a difficult battle. They are constantly at risk of respiratory infection and pneumonia. Feeding difficulties make it a real challenge for parents to give their children adequate nutrition and supplemental feedings may be required. Tubes placed through the nose or directly onto the stomach may be necessary. Recurrent respiratory problems usually result in death before two years of age. However, a small number of children with Type I SMA may survive into their teens or early adulthood.
Although the preceding classification of spinal muscular atrophy is useful to patients, families, and the medical team working with them, it must be emphasized that SMA Types I, II, and III (and in some cases SMA Type - IV) represent a continuum. Additional understanding of the gene defects will undoubtedly explain the tremendous clinical variation that children and young adults with SMA demonstrate.
the above was written for Fight SMA by: Robert T. Leshner, M.D., Professor, Neurology and Pediatrics, Children's National Medical Center