Spinal muscular atrophy is a rare degenerative genetic disorder that affects the spinal cord and nerves, resulting in muscle wasting and weakness. SMA is an autosomal recessive disease. This means that both males and females are equally affected, and that two copies of the gene, one inherited from each parent, are necessary to have the condition. A gene called survival motor neuron (or SMN) is found to have an abnormal area (either a deletion or extra copy of the gene) in over 95 percent of cases of SMA. When both parents are carriers, there is a one in four, or 25 percent, chance, with each pregnancy, to have a child with SMA.
There are four different types of SMA based on strength levels and age when regression begins.
Type 1 is the most severe type of SMA, sometimes referred to as Werdnig-Hoffman. The onset of symptoms can occur anywhere from in utero to 6 months old. Infants have problems holding their head, sucking, feeding, swallowing and typically move very little. Key indicators for children are tongue fasciculations (or tremors). These children may have to have a tracheotomy to sustain life and typically require a feeding tube for nutrition. They are usually never able to sit independently. Respiratory issues are the primary concern as their chest muscles are underdeveloped and they are unable to produce a cough to remove mucus or secretions. Pneumonia is common in these kids and respiratory problems are a huge concern and ultimately lead to their demise.
The Type 2 is typically diagnosed between 6 and 18 months. These children probably developed normally until at least 6 months of age and then began to regress. They have generalized muscle weakness and may require braces, walkers and wheelchair for assistance. It is not uncommon for these children to survive into their 20s-30s. They may have some of the respiratory problems and swallowing problems later in life, but no to the extent of of the Type 1.
Type 3 usually begins as clumsiness and begins to show after 18 months of age. These children have difficulty walking, mild muscle weakness, and may experience developmental delays. These children are able to live long into their adult years.
The Type 4 is a walking disability that occurs in adulthood. This is by far the most mild form of SMA.
There is no treatment or cure for any of the types of SMA. The ultimate goal is to prevent respiratory problems and to provide proper nutritional monitoring, especially in those children with compromised swallows.
