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Spinal Muscular Atrophy (SMA) is a motor neuron disease. The motor neurons affect the voluntary muscles that are used for activities such as crawling, walking, head and neck control, and swallowing.

It is a relatively common “rare disorder”: approximately 1 in 6000 babies born are affected, and about 1 in 40 people are genetic carriers.

SMA affects muscles throughout the body, although the proximal muscles (those closest to the trunk of one’s body – i.e. shoulders, hips, and back) are often most severely affected. Weakness in the legs is generally greater than in the arms. Sometimes feeding and swallowing can be affected. Involvement of respiratory muscles (muscles involved in breathing and coughing) can lead to an increased tendency for pneumonia and other lung problems.

Sensation and the ability to feel are not affected. Intellectual activity is normal and it is often observed that patients with SMA are unusually bright and sociable.

Patients are generally grouped into one of four categories, based on certain key motor function milestones (Types 1, 2, 3 & 4) Type 1 is the most severe form of the disease, type 4 the least severe.

SMA is a genetic disease where both parents are carriers. 2 carrier parents have a 25% chance of parenting a child with SMA. They would have a 50% chance of parenting a child that is a carrier of SMA. They would have a 25% chance of parenting a child that is not a carrier and also does not have the disease.

See also Understanding SMA. Print copies of this booklet are available by contacting our office.