About SMA

Spinal Muscular Atrophy (SMA) is a motor neuron disease that causes muscle weakness and atrophy (wasting).  The motor nerves arise from the spinal cord and control the muscles that are used for activities such as breathing, crawling, walking, head and neck control, and swallowing. SMA is a rare disorder occurring in approximately 8 out of every 100,000 live births, and affecting approximately 1 out of every 6,000 to 10,000 individuals worldwide. 

SMA is caused by a missing or abnormal (mutated) gene known as survival motor neuron gene 1 (SMN1). In a healthy person, this gene produces a protein in the body called survival motor neuron (SMN) protein. In a person with mutated genes, this protein is absent or significantly decreased, and causes severe problems for motor neurons. In order for a child to be affected by SMA, usually both parents are carriers of the abnormal gene and pass this gene on to their child. Thus the child has 2 abnormal copies of the gene, one from each parent, and this is termed a recessive genetic disease. When both parents are carriers, the possibility of a child inheriting the disorder is 1 in 4, or 25%, with each pregnancy. About 1 in 40 people are genetic carriers. Carriers have no symptoms and often don't know they are carriers until they have a child diagnosed with SMA.

SMA affects muscles throughout the body. In the most common types, weakness in the legs is generally greater than in the arms. Sometimes feeding, swallowing, and respiratory function (e.g., breathing, coughing, and clearing secretions) can be affected. When the muscles used for breathing and coughing are affected and weakened, this can lead to an increased risk for pneumonia and other respiratory infections, as well as breathing difficulty during sleep. The brain’s cognitive functions and the ability to feel objects and pain are not affected. People with SMA are generally grouped into one of four types (I, II, III, IV) based on their highest level of motor function or ability.

http://www.curesma.org