Spinal Muscular Atrophy (SMA) is a hereditary disorder in which the nerve cells that control the skeletal muscles of the trunk and limbs are affected. The disease is transmitted autosomal recessive, i.e. it is not sex-linked and both parents must be carriers. They transmit the disease without suffering from it themselves. Their children have 25% chance of contracting the disease, 50% chance of being carriers and 25% chance of not inheriting the genetic abnormality.
Loss of neuronal cells in the first months of life leads to muscle weakness and atrophy (shrinkage), which becomes visible at the age of 3 to 4 months. When they are 5 to 6 months old, their back is so weakened that they have difficulty jumping on furniture and often land in a clumsy way when jumping down. Because they are unable to move sufficiently, the spine, knees, elbows and feet can become deformed. The respiratory and swallowing muscles are not affected but due to deformity of the spine (scoliosis) there is a risk of respiratory infections or pneumonia. If the muscles used for chewing are affected, eating can be more difficult. The sooner the disease progresses, the more serious it becomes.