About Spinal Muscular Atrophy


Spinal muscular atrophy (SMA) is a rare genetic disorder that affects the voluntary muscles that are used for activities such as crawling, walking, head and neck control, and swallowing. It refers to a group of diseases that affect the motor neurons of the spinal cord and brain stem.


Approximately 1 in 6,000 babies born are affected and about 1 in 40 people are genetic carriers. Both parents must have the SMA trait in order to pass the gene on. If such a situation should occur, then there’s a 25% chance that the child will be born with SMA.


Although SMA affects muscles throughout the body the shoulders, hips, and back are most severely affected. There’s generally weakness in the legs that will lead to limited or no walking ability as well as activities such as feeding and swallowing are affected. SMA patients may not be able to breathe properly and have an increased tendency for pneumonia and other lung problems.


The ability to feel is not affected and intellectual activity is normal. It is often observed that SMA patients are unusually bright and sociable.


There are four types of SMA; type I, II, III, and IV. It has been observed that patients universally tend to loss function as they age.


Type I SMA, or Werdnig-Hoffman Disease is generally diagnosed before 3 months of age. Usually a child is unable to accomplish normal motor skills expected early on in infancy. Swallowing, breathing is affected and the child may have a smaller chest due to the weakening of the intercostal muscles (the muscles between the ribs) that help the chest expand.


Type II SMA is almost always diagnosed before the child turns 2. With this type of SMA the child will be able to sit unsupported and may even stand at some point, but will require assistance to walk. Breathing problems, scoliosis, and decreased bone density are all characteristic of this type of SMA.

Type III SMA, or Kugelberg-Welander is much more variable in the age of onset. This type of atrophy can present itself from a year of age to as late as adolescence. Type III individuals can sometimes lose their ability to walk later in childhood, adolescence or even adulthood.


Type IV SMA is adult onset. Symptoms typically begin after 35. The progression is very slow and insidious. Patients lose some muscular abilities as they age.


Are you a carrier and/or your spouse a carrier of SMA?


Seek the advice of a genetic counselor. The counselor can help you to better understand the risks and chances of having an affected child.

Spinal Muscular Atrophy causes death in more babies than any other genetic disease. It can be diagnosed through a blood test, so if you suspected of your child of having SMA, consult your pediatrician or family physician for more information.