What is Spinal Muscular Atrophy?
Spinal Muscular Atrophy (SMA) is an inherited neuromuscular condition that affects nerve cells in the spinal cord called anterior horn cells. Messages from the brain travel down the spinal cord, through the anterior horn cells, then along motor neurons to the muscles telling them to move. In SMA, the anterior horn cells fail to provide an effective link between the brain and the muscles. Messages are blocked or distorted. This causes the muscles to waste away (atrophy). The motor neurons affected in SMA are those which enable walking, crawling, arm and hand movement, head and neck movement and swallowing. The muscles used in breathing can also be affected. The brain and sensory nerves, which allow us to feel sensation such as temperature and touch, are not affected in SMA.
SMA is a relatively rare disease that affects approximately 1 in 6500 babies born. That means about 100 new cases are diagnosed each year. Approximately 1 in 40 of us carry the genetic mutation that causes the condition. There are 4 main types of SMA. Types 1, 2 and 3 appear in childhood. The fourth type affects adults, and is known as Adult Onset SMA. Other rarer forms of SMA include SMA with Respiratory Distress (SMARD), Spinal Bulbar Muscular Atrophy and Distal SMA. SMA types 1, 2 and 3 are termed autosomal recessive. This means that for a baby to be affected, both parents must be carriers of the faulty gene. In these circumstances, there is a 1 in 4 chance in each pregnancy of the baby being affected by SMA. The inheritance pattern of the adult and rarer forms of SMA can be different from the childhood forms.
All types of SMA produce muscle weakness but in varying degrees of severity. Type 1 SMA is the most severe and is usually fatal within two years of birth.
Please click on the relevant type of SMA to see the available information.
